![~ChaPter3
- What is the difference between#include and import statement?
,I
#include directive makes the f:ompiler go to the C/C++ standard library and copy the code from
'the header files into the program. As a result, the program size increases, -thus wasting memory and
processor's time. -
import statement makes the JVM go to the Java standard library, execute the code there, and
substitute the result into the program. Here, no code is copied and hence no waste of memory or
pt:ocessor's time, So, import is an efficient mechanism than #include.
Mter importing the classes into the program, the next step is to write a class, Since Java is purely
an object-oriented programming language, we cannot write a Java program without having at least
one class or object. So, it is mandatory that every Java program should have at least one class in it,
How to write a class? We should use class keyword for this purpose and then write the class name.
u51ic statlc Vela maln Strln ar 5
Next to main () method's name, we have written String args []. Before discussing the
main () method, let us fIrst see how a method works, A method, gen~rally, performs two functions.
D It can accept some data from outside
D It can also return some result
A class code starts with a { and ends with a }. We know that a class or an object contains variables
and methods (functions), 'So we can create any number of variables and methods inside the class.
This is our fIrst program, so we will create_ onlY.one method, i.e. compulsory, in it-main () method.
Why should we write main {} method? Because, if main () method is not Wlitten in a Java program,
JVM will not execute-it. main (} is the starting point for JVM to start execution of a Java program,
r 5
i CSt 'n
Let us take sqrt () method. This method is used to cal9ulate square root value -of a given number.
So, at the time of calling sqrt n method, we should pass a number (e.g~ 16) for which we want to
calculate square root, Then, it calcula_tes square root value and returns the result (e,g. 4) to us.
Similarly, main () method also accepts some data from us, For example, it accepts a group of
strings, which is also called a string type array, This array is String args [] , which is written along
with the main n method as:
I
Here args [] is the array name and it is of String type. This means that it can store a group of
strings, Remember, this array can also store a group of numbers but in the form of strings only. The-
values passed to main () method are called arguments. These arguments are stored into args []
-array, so the name args [] is generally used for it.
Amethod can return some result. If we want the method to return the result in form of an integer,
then we should write int before the method name. Similarly, to get the result ill string form or as a
single character, we can write string or char before it, respectively. If a method is not meant to
return any value, then we should write void before that method's name. void means no value.
main () method does not return any value, so void should be written before that method's name.
A method is executed only when it is called, But, how to call a method? Methods are called using 2
steps in Java.](https://image.slidesharecdn.com/3519386-250628154039-67c5b488/85/Core-Java-An-Integrated-Approach-2nd-R-Nageswara-Rao-37-320.jpg)
![First Steps towards Java Programming l.2!.
1. Create an object to the class to which the method belongs. The syntax of creating the object is:
I
2. Then the ~ethod should be called using the obj ectname .methodname () .
Since main () method exists in the class First; to call main () method, we should first of all create
an object to First class, something like this:
Then call the main () method as:
j.m i
So, if we write the statement:
- ,
",side the main () method, then JVM will execute this statement and create the object.
r class Fi rst
{
y looking at the code, we can understand that an object could be created ocly af!er callin~ the·
main () method. But for calling the main·() method, fIrst of all we require an object. Now, how'is it
possibl~ to cr~ate an object before callmg the main () method? So, ~e should- call the main·()
method without creating an" object. Such met.hods are called static methods and should be declared
as static.
Static methods are the methods, which can be called and executed without creating the objects.
Since we want to call main () method without using an object, we should declare main () method as
static. Then, how is the main () method called and executed? The answer is by using the
classname .methodname (). JVM calls main () method using its dass name as First .main () at the
time of running the program.
JVM is a program written by JavaSoft people (Java development team) and main () is the method
written by us. Since, main () method should be available to the JVM, it should be declared as
public. If we don't declare main () method as public, then. it doesn't make itself available to JVM
and JVM cannot execute it:
So, the main () method should always be written as shown here:
If at all we want to make any changes, we can interchange public and static and write it as
follows:
(jl)] lC](https://image.slidesharecdn.com/3519386-250628154039-67c5b488/85/Core-Java-An-Integrated-Approach-2nd-R-Nageswara-Rao-38-320.jpg)
![Till now, according to our discussion, our Java program looks like this:
'-
22.J Chapter 3
Or, we can use a different name for the string type array and write it as:
[
args'[] is not written in main () method?
When rnai n () method is written without S t r ing a rgs [J as:
public static void main ()
the code will compile but JVM cannot run the c,Ode because it cannot recognize the main () method as
the method from where it should start execution of the Java program. Remember JVM always looks for
main () method with sti-ing type arr!!y as parameter.
Our aim of writing this program is just to display a string "Welcome to Java". In Java, print ()
method is used to display something on the monitor. So, we can write it as:
But this is not the correct way of calling a method in Java. A method should be called by using
objectname .methodname (). So, to call print () method, we should create an object to the class to
which print () method belongs. print () method belongs to PrintStream class. So, we should call
print () method by creating an object to printStrea~class as:
But as it is not possible to create the object to PrintStream class directly, an alternative is given to
us, i.e. System. out. Here, System is the class nam~and 01l;t is a static variable in System class. out
is called afield in System class. When we call this field, a PrintStream class object will be created
internally. So, we can call the print () method as shown below:
System. out gives the PrintStream class object. This object, by default, represents the standard
output device, i.e. the monitor. So, the string "Welcome to Java" will be sent to the monitor.
Now, let us see the final version of our Java program:](https://image.slidesharecdn.com/3519386-250628154039-67c5b488/85/Core-Java-An-Integrated-Approach-2nd-R-Nageswara-Rao-39-320.jpg)
![~ Chapter 3
We know that a class contains variables and methods. Even if we do not creste variables or
methods, we should write at least one method, Le. main (). The purpose of writing the main()
method is to make JVM execute the statements within it. Let us take ariexample:
Here, main () method is declared as public, static, and void. public because it should be made
available to JVM, which is another program; static because it should be called without using any
object; -and void because it does not return any value. Also, after the method name, we write
String args [] which is an array to store the values passed to main () method. These values
passed to main () are called arguments. These values are stored in args [] array in the form of
strings.
Inside the main () method, let us write the code to fi..'1d the sum of two numbers. Observe the full
program now:
- Program 2: To find the sum of hvo numbers.
numoers
jjdisplay resul<t
system.out.print(z);
Output:
In the above program, inside main () method, we write the first statement as:
int x](https://image.slidesharecdn.com/3519386-250628154039-67c5b488/85/Core-Java-An-Integrated-Approach-2nd-R-Nageswara-Rao-41-320.jpg)
![.22.JChapter 4
What is the difference between float and double?
Floa t can represent up to 7 digits accurately after decimal point, whereas daubl e can represent up
to 15 digits accurately after decimal point.
Let us now look at an example given here:
float i 3.'D12}i';
Here, the variable pi is containing the value 3 .142. I~ F is not written at the end, then JVM ~ould
have allotted 8 bytes assuming the value to be double. The reason for this is that in float and
double data types, the default is taken as double. By attaching F or f, we can ask the JVM to
consider it as a float value and allot only 4 bytes.
double distance=1.98e8;
Here,e or E represents X 10 to the power. Hence, 1. 98e8 means 1. 98X108. This is also called
scientific notation of re~resentingnumbers.
Character Data Type
This data type represents a single character like a, P, &, *, etc. Table 4.3 shows char data type
details.
Table 4.3
Data type Memory size Minimum and Maximum values
Char 'II .." 2 bytes ;i't oto 65535 ."F ~ .,"1
Here is an example of character data type:
cfla:f en ~X"
Here, we are storing the single character 'x' into the variable ch. Here, 'X' is also called characte7
literal. WHenever character literals are written, they should be enclosed inside the single quotes.
By observing the minimum and maximum values in the table earlier, we shall get a doubt regarding
why the range is expressed in integer numbers (0 to 65535). We know that all the characters on the
keyboard are translated into integer values called ASCII (American Standard Code for Information
Interchange), which is a standard maintained by every keyboard manufacturer. The processOI
recognizes the character uniquely from its ASCII value. Hence, let us understand the' range
mentioned in the table is nothing but the ASCII value range only.
The ASCII value range, from 0 to 65535, given in the table can uniquely represent a total of 6553E
characters. This means a total of 65536 distinct characters can be recognized by Java. But we nevel
use these many characters since our keyboard contains English alphabets and some othe]
characters whose total does not exceed 256. This means 1 byte is s'Ufficient to represent all th<
available characters of the keyboard. Then why 2" bytes are used to represent the char data type ir
Java?
JavaSoft people wanted to provide a facility to include characters not only from English but alS(
from all other human languages to be used in Java programs. This will enable the programmers t(
write and execute a Java program in any language, which becomes an advantage on Internet. Thi1
system is also called Unicode system. Unicode uses 2 bytes so that any character from any languagl
can be encoded successfully.](https://image.slidesharecdn.com/3519386-250628154039-67c5b488/85/Core-Java-An-Integrated-Approach-2nd-R-Nageswara-Rao-49-320.jpg)
Core Java An Integrated Approach 2nd R Nageswara Rao
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- 6. About the Author Mr. R Nageswara Rao has been associated with teaching Computer Science since 1993. He has worked at various colleges as HOD (Dept. of Computers) and as a free-lance developer for some time for a cpuple of organizations. He has been teaching Java since 2000, and is currently associated with INet Solv Solutions, Hyderabad, a prestigious training division, imparting specialized training in Java. Mr. R Nageswara Rao is teaching and interacting with more than 1000 new students every month, including software developers and foreign students. Since 1998, Mr. Rao is associated with 'Computer Vignanam', a widely circulated monthly magazine, published in Telugu. He has been on the editorial board of this magazine for the past six years. He published several articles, including articles on Virtual Reality, Mobile communications, Blue tooth technology and Global positioning systems. He also published hundreds of articles on C/C++ and Java.
- 7. Content at a Glance Core Java - An Integrated Approach Chapter 1 - All about Networks 1 Chapter 2 - Introduction to Java 7 Chapter 3 - First Step Towards Java Programming 15 Chapter 4 - Naming Conventions and Data Types : 27 Chapter 5 - Operators in J§l-va 33 Chapter 6 - Control Statements in Java 47 Chapter 7 - Input and Output 65 Chapter 8 - Arrays 81 Chapter 9 - Strings 95 Chapter 10 - StringBuffer and String Builder 107 Chapter 11 - Introduction to OOPs ~ 115 Chapter 1j; Classes and Objects 123 Chapter 1J.-- Methods in Java : ,' :. 139 Chapter 14 - Relationship Between Objects 169 Chapter~-Inheritance 183 Chapter ~ Polymorphism ,' 197 Chapter 17 - Type Casting -. 209 Chapter(Bl7- Abstract Classes -. 223 Chapter 19""- Interfaces 233 Chapter ~Packages 245 Chapter@- Exception Handling 265 Chapter 22 - Wrapper Classes 283 Chapter 23 - The Collection framework 297 Chapter 24 - Streams and Files 333 Chapter 25 - Networking in Java 357 Chapter&- Threads 375 Chapter 27 - Graphics Programming using AWT 409 Chapter 28 - Graphics Programming using Swing 459 Chapter 29 - Graphics Programming - Layout Managers 523 Chapter 30 - Applets : 545 Chapter 31 - Generic Types 563 Chapter 32 - Java Database Connectivity 571 Index I - Question Index ; ; 621 Index II - Program Index ~ 629
- 8. no Table of Contents Preface ; XXI _Chapter 1: All ab-out Networks : ~: : 1 What Comprises the Internet? - 2 How does Internet·Function? 3 Software Development for Internet 3 - . Chapter 2: Introduction to Java : : 7 Features of Java 7 The Java Virtual Machine 10 Differences between C++_and Java: 13 Parts of Java 13 Chapter 3: First Step towards Java Programming•.....•...•....................•...•.......•.....•...........15 API Document : _ 16 Starting a Java program : 16 Importing classes : ~ 16 Formatting the Output 23 Chapter 4: Naming Conventions and Data Types 27 Naming Conventions in Java- : , : ~ ~ 27 Data Types in Java : : 28 integer Data Types : .- : .- 29 Float Data Types 29 - - . . .-- .'.- Character Data Type 30 String Data Types 31 Boolean Data Types : : : : : ~ : 31 Literals : : 31 Integer Literals...........................................................................................................•: 32 Float Literals : : 32 Character Literals 32 String Literals :: 32 Boolean Literals _ .'.~ 32 Chapter 5: Operators in Java 33 Operators : : 33 Arithmetic Operators 33 Unary Operators : : :.. 34 Increment Operator (++) : 34 Decrement Operator (--) 36 Assignment Operator (=) , - 36 Relational Operator : 37 ml s
- 9. ~ Core Java - An Integrated Approach Logical Operators : 38 Boolean Operators - 38 Bitwise Operators 39 Ternary Operator or Conditional Operator ( ? : ) 43 instanceof Operator ~._: 45 new Operator , , 45 Cast Operator ~ .-- 45 Priority of Operators : 45 Chapter 6: Control Statements in Java 47 < • • if. ..else Statement 48 do::.while Loop : ; 49 while Loop _ 50 for Loop 51 Nested for Loops 54 for-each Loop ~ :.: 55 switch Statement - 56 break Statement..; : ; ,: 58 continue Statement · ; ;..;- .--.: 60 return Statement 62 - Chapter 7: 'Input and Output: 65 Accepting Input from the Keyboard : , : : 65 Acc.epting a Single Character from the Keyboard : 67 Accepting a String from Keyboard : : 68 Accepting an Integer value from the Keyboard 69 Accepting a Float Value from Keyboard : 70 Accepting a Double Value ; 70 Accepting Other Types of Values .- : 70 Accepting Different Types of Inputs in a Line 73 Reading Input withjava.util.Scanner Class 78 Displaying Output with' System.out.printfO 79 Displaying Formatted Output with String.formatO .- 80 Chapter 8: Arrays 81 Types of Arrays : 81 Single Dimensional Arrays (1 D array) : 82 Multi Dimensional Arrays (2D, 3D, arrays) , 86 Three dimensional arrays (3D array) 89 arrayname.length .- 91 Command Line Arguments 91 Chapter 9: Strings - : 96 Creating Strings : 95
- 10. Table of Content ~ String Class Methods - 96 String Comparison : , 100 Immutability of Strings 103 Chapter 10: StringBufTer and StringBuUder : 107 Creating StringBuffer Objects , 107 StringBuffer Class Methods : ~ 108 StringBuilder-Class , : - 112 StringBuilder Class Methods 112 Chapter 11: Introduction to OOPs 115 Problems in Procedure Oriented Approach .:.:= : , 116 Features of Object Oriented Programming System (OOPS) 116 Class/object 117 En.capsulation : : i 19 Abstraction 120 Inheritance ~ - ~~ 120 Polymorphism 121 Chapter 12: Classes and Objects , : - 123 Object Creation : : 124 Initializing the Instance Variables 127 Access Specifiers 129 Constructors 130 Chapter 13: Methods in Java : : 139 Method,Header or Method Prototype : 139 Method Body - :~ 140 Understanding Methods .- 141 Static Methods - .- 145 Static Block : : : 149 The keyword 'this' : : 151 "'- . . Instance Methods : 153. Passing Primitive Data Types to Methods , 154 Passing Objects to Methods 155 Passing Arrays to Methods , ~ , 158 Recursion - : 162 . Factory Methods , : : : 164 Chapter 14: Relationship Between Objects 169 Relating Objects using References 169 Inner Class .- -.174 Anonymous Inner Class 178
- 11. XlV ICore Java - An Integrated Approach Chapter 15: Inheritance ; - 183 Inheritance c •••••••••••••••••.••• : •••• 183 The Keyword 'super' - 188 The Protected Specifier : 192 Types of Inheritance · : 194 Chapter 16: Polymorphism 197 Polymorphism with Variables 197 Polymorphism using Methods : 198 Dynamic Polymorphism :.. 198 Static Polymorphism _ .. 202 Polymorphism with Static Methods : 203 Polymorphism with Private Methods - 204 Polymorphism with Final Methods 204 . final Class 205 Chapter 17: Type Casting , 209 Types of Data Types ; 209 Casting Primitive Data Types 210 Casting Referenced Data Types : :- 211 Generalization and Specialization : 211 The Object Class :.:.· 217 Cloning the Class Objects 220 Chapter 18: Abstract Classes 223 Abstract Method and Abstract Class 224 Chapter 19: Interfaces 233 Interface 233 Multiple Inheritance using Interfaces 246 Abstract Classes vs. Interfaces 242 Chapter 20: Packages.......•........•••.....~........•.....••................................................:: 245 Package - 245 Different Types of Packages : 246 - Built-in Packages 246 User-defined Packages 247 The JAR Files ..; ; : 253 Interfaces in a Package 255 Creating Sub Package in a Package 257 Access Specifiers in Java : ~ 258 Creating API Document 261
- 12. Table of Content ~ Chapter 21: Exception Handling ;..~ 265 Errors in a Java Program : ~.~ ;: 265 Exceptions ~., : , 267 ~ Exception Handling : 269 Handling Multiple Exceptions : 271 throws Clause 273 throw Clause 275 . Types of Exceptions : : ~ ~ 276 Built-in Exceptions 277 User-defined Exceptions 277 Re-throwing an Exception ; : :· 279 Chapter 22: Wrapper Classes 283 Wrapper Classes ~ ~ 283 Number Class : 284 Number Class Methods 284 Character Class : 285 Important Methods of Character Class 285 Byte Class 287 Constructors : 287 Important Methods of Byte Class 287 Short Class 288 Constructors '.- 289 Important Methods of Short Class , 289 . ' . Integer Class 289 Constructors .............................................................................................................•......... 289 Important Methods of Integer Class ; 290 Long Class 291 Constructors 291 Important Methods of Long Class : ,' 291 Float Class 292 Constructors 292 Important Methods of Float Class ~ : 292 Double Class 292~ . - Constructors 292 Important Methods of Double Class 293 Boolean Class 293 Constructors 293 Important Methods of Boolean Class: : 293 Math Class : 294 Important Methods of Math Class : ~ : 294
- 13. XVI ICore Java - An Integrated Approach Chapter 23: The Collection Framework 297 Using an Array to Store a Group of Objects , 297 Collection Objects y ••••••• : •••••••••••••••••••••••••••••••• ..........................................................· •••• 299 Sets 300 Lists : 300 Queues : 300 Maps 300 Retrieving Elements from Collections :.:; 301 for-each Loop 301 Iterator Interface 301 Listlterator Interface 301 Enumeration Interface 302 HashSet Class ' : : 302 HashSet Class Methods : 302 LifikedHashSet Class : : 303 Stack Class : 304 Stack Class Methods : 305 LinkedList Class : 307 LinkedList Class Methods : 308 ArrayList Class · : 310 ArrayList Class Methods .-= : : •• : : 311 Vector Class : 312 Vector Class Methods 313 , HashMap Class : : : 315 HashMap Class Methods : : 316 Hashtable Class : 318 Hashtable Class Methods 319 Arrays Class; : , : , 322 Arrays Class Methods : : 322 Using Comparator to Sort an Array : 324 StringTokenizer Class : 326 StringTokenizer Class Methods : 326 Calendar Class ; 327 Calendar Class Methods 327 Dl;tte Class 328 Chapter 24: Streams and Files , - 333 Stream : .- 333 Creating a me using FileOutputStream 336 Improving Efficiency using BufferedOutputStream : 338 Reading Data from a File using FileInputStream : 340 Creating a File usirtg FileWriter : 342 Reading a File using FileReader 343
- 14. Table of Content.E Zipping and Unzipping Files : 344 Zipping a File using DeflaterOutputStream : 345 Unzipping a File using InflaterlnputStream.: : 346 Serialization of Objects ....................................................•.................~ : 347 Counting Number of Characters in a File : 351 File Copy : 352 File Class 353 File Class Methods : 353 Chapter 25: Networking in Java 357 TCPlIP ProtocoL 357 User Datagram Protocol (UDP) 359 Sockets 359 Knowing IP Address 360 URL. : 361 URLConnection Class : 362 Creating a Server That Sends Data : 364 Creating a Client That Receives Data· 365 Two-way Communication Between Server and Client 368 Retrieving a me at server '- 370 Chapter 26: Threads 375 Single·Tasking 376 Multi Tasking : 377 Uses of Threads : 378 Creating a Thread and Running it : : .. 379 Terminating the Thread ' 381" Single Tasking Using a Thread 382 Multi Tasking Using Threads 383 Multiple Threads Acting on Single Object 385 Thread Class Methods ; : 389 Deadlock of Threads 390 Avoiding Deadlocks in a Program 393 Thread Communication 394 Thread Priorities : 399 Thread Group 400 Daemon Threads 402 Applications of Threads · 402 Thread Life Cycle ~ 406 Chapter 27: Graphics Programming using AWT ;; 409 AWT 409 Components 410 Window and Frame , 410
- 15. xviii ICore Java - An Integrated Approach Creating a Frame ................•..................................................................................................... 411 Event Delegation Model : 413 Closing the Frame _ 415 Uses ofa Frame ~ 418 Drawing in the Frame 419 Filling with Colors 421 Displaying Dots - 426 Displaying text in the frame 427 Knowing the Available Fonts , 429 Displaying Images in the Frame : ' 430 Component Class Methods 432 Push Buttons -. 433 Listeners and Listener Methods 438 Check Boxes : 440 Radio Button ~ .......................•................ 442 TextField .....................................................................................•...................- - , 444 TextArea 444 Label , - :.:-,..•............ 445 Choice Class 447 List Class 449 . Scrollbar Class ~ 452 Knowing the Keys on Keyboard : :.454 Working with Several Frames 456 Chapter 28: Graphics Programming using Swing 459 Java Foundation Classes (JFC) 459 Packages of JFC ;.. 460 javax.swing ~d MVC - : 460 Window Panes '. 461 Important Classes ofjavax.swing 463 Creating a Frame in Swing 463 Displaying Text in Frame 466 JComponent Class Methods 469 Creating a Push Button with All Features : , 475 . Displaying Image in Swing 476 Creating Components in Swing 479 SettiI:g the Look and Feel of Components 482 JTable Class 485 JTabbedPane Class 489 JSplitPane Class 491 JTree Class 493 JComboBox Class 497 JList Class : .- 499
- 16. tiFF Table of Content ~ .JMenu Class : 502 JToggleButton Class.: :- 509 JProgressBar Class 511 .JToolBar Class · »'••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 514 s JColorChooser Class 516 Handling Keyboard Events : 517 Handling Mouse Events 519 Chapter 29: Graphics Programming - Layout Managers ~.523 FlowLayout .- : ~..:.. 524 BorderLayout - 525 CardLayout - 527 Using a Layout Inside Another Layout.. 529 GridLayout : : 532 GridBagLayout : :.................................•. 533 BoxLayout .- .- 539 Box Class : ; 541 Chapter 30: Applets : 545 Creating an Applet ; 545 Uses of Applets .- 547 <APPLET> tag 547 A Simple Applet : 548 An applet with Swing Components 550 Animation -in Applets , 553 A siri:J.ple Game with an Applet 557 Applet Parameters 5~9 Chapter 31: Generic Types 563 Generic Class :: 563 Generic Method : 566 Generic Interface .- 567 Chapter 32: Java Database Connectivity 571 Database Servers 571 Database Clients 572 JDBC (Java Database Connectivity) 573 -Working with Oracle Database :.- _ .- 574 Working with MySQL Database 576 Stages in a JDBC Program , 578 Registering the Driver 579 Connecting to a Database 580 Preparing SQL Statements 581 Usingjdbc-odbc Bridge Driver to Connect to Oracle Database ; 586
- 17. xx ICore Java - Ail Integrated Approach Retrieving Data from MySQL Database 588 Retrieving Data from MS Access Database , 590 Improving the Performance of a JDBC Program : 592 (a) Affect of Driver. 593 (b) Affect of setFetchSlzeO 595 (c) Affect of PreparedStatement 597 Stored Procedures and CallableStatemerit 599 Types of Result Sets 603 Storing Images Into Database : ~ 607 Retrieving Images From Database 609 Storing a file into database 610 Retrieving a File from the Database , 611 ResultSetMetaData '" , 613 DatabaseMetaData : ' 614 Types of JDBC Drivers ; 616 Question Index , ; : 621 Program Index ; , ;.629
- 18. I l , Preface The importance of Java language cannot be denied as it has already started ruling over the entire Software Industry. Companies have started recruiting programmers but there is still a dearth of Java programmers. I set teaching as my profession in 1993, and have ever since engaged my time in teaching and training thousands of students in Computer Sciences. Since 2000, I started teaching Java to students. When my students asked me to prescribe a book for their reference, I naturally thought of writing an ideal book for them that would fulfill the following goals: o The book should be written in such a way that learners without any background in programming should be able to follow it and understand it entirely. This meant that the book should discuss the concepts of Java in a simple and straightforward language with a clear-cut explanation, without.beating about the bush. o Once the students understood the book, they should be able to at least write simple programs on their own, as this is the first requirement to become a Java programmer. It meant the book should provide ample solved programs, which could be used by the students not only in their examinations but also to remove the fear of programming from their minds. o After reading 'the book, the students should have the' confidence to apply for a· software development company, face the interview board and come out successful. It meant the book should also cover sample interview questions, which were asked in various interviews. This would help the students to prepare well for their future careers. I searched the market for such a book and to my dismay, I could not found a single one. I found- some books that provided the concepts, but were lacking in programming examples. A few books gave programs without any insight into the concepts. None of them was useful to learn Java. To address this need, I thought of writing a book on Java with a three-stage formula: concepts + programs + interview questions. The result of my endeavour is the book you have in your hands now! "- Since many students are opting for Computers or IT as the subject of their study, there is a growing need for them to learn Java from the ground up as well as learn good programming skills, and finally pursue a career in software development as a Java professional. ,This book will help them achieve these goals by following a three-stage process focusing on understanding Java, writing programs, and facing interviews. Many Indian students may wish to use this book to solve the programs generally asked in their exams, since this book covers programs such as generating the Fibonacci number series, finding prime, generating primes, finding the product of matrices, creating subclasses such as rectangle, circle, triangle from a super class, creating interfaces, and so on. Such programs are commonly asked in the exams of Indian universities, at B.C.A, B.Sc, M.Sc, M.C.A and Engineering levels. The coverage of interview questions along with the subject matter will help students do well in interviews. The questions presented in this book have been collected from various interviews conducted by top companies while recruiting the candidates. What this book contains This book has 32 chapters in all, arranged in increasing order of complexity. Hence, it is advised that readers start reading this book from the beginning unless they have some previous knowledge of the subject. The first ten chapters will help bring readers from the novice stage to a stage where they will have gained a proper understanding the fundamentals. These chapters cover the concepts of Java and JVM along with the basic elements of writirig a Java program. I- .-t Ilii IIIIIIiiI._
- 19. xxii Chapter 11 is on OOPS, and covers the concepts on which the Java language was built. The subsequent chapters explain these concepts (Classes, Objects and Methods) with programs. Inheritance and Polymorphism, two powerful features of an OOP language, are covered in chapters 15 to 17. Abstract classes and interfaces are discussed in chapters 18 and 19. Once the software is developed, packaging the classes and providing an API document are necessary. These issues are discussed in Chapter 20. Handling errors and exceptions that occur in a Java program are discussed in Chapter 21, while Chapter 22 discusses how to convert fundamental data into object form. • Chapters 23 to 32 are devoted to advanced concepts. The process of arranging various objects in the memory comes under the collection framework, which has been described in Chapter 23; Chapter 24 tells you how to create fIles using streams; Chapter 25 shows you how to create client and server programs for a network; and, Chapter 26 covers Threads. Chapters 27 to 30 discuss the GUI programs, which provide all enhanced user experience. Chapter 31 is on Generics and Chapter 32, the last chapter of the book, deals with writing Java programs to communicate with any database. Version used in this book While this book is not a complete reference, it covers all core concepts in a methodical way. The focus is on the important concepts and not on version-specific issues. Hence, you can use this book to learn Java without worrying too much about the version. .
- 20. CHAPTER ALL ABOUT NETWORKS d W e shall begin this chapter with an understanding .of networking concepts and proceed further to kriow why languages, like CjC++, are not opted for a network and why Java is a language suited for a network, especially Internet. _ InterconnectiQn of computers is called network. A network may contain two or more computers connected with or without a cable. For example, you can connect a computer in Delhi to one placed. in.Hyderabad with the help of a satellite and data can be sent or received via satellite in the form of electromagnetic waves. So, a network mayor may not have a cable. The primary purpose of a network is resource sharing, which means a computer can share its resources, like data, memory, software, hardware, CPtJ, etc. with other computer.s on the network. In the network, one computer may ask the other computer for some service. The computer, which requests for some service is called client and the other computer, which provides that service to the client· is called' server. A network can have several clients and servers and such a network architecture is also called a client/server architecture. Figure 1.1 shows a client jserver architecture. Here, you can see that the request goes from the client to the server and the server gives back the response. request - ... Client i Server ... response Client sends request for service. Server sends response to client. Figure 1.1 A network with two computers ,
- 21. ~--_. 2.JChapter 1 Now, let us see how we can connect one computer to another. Following are the requirements for setting up a network of computed's: What is the advanta{Je of a netw?rk? The main advantage of a (,Ie~ork is that it makes resource sharing possible among the connected systems, thus helping in better utilization'of resources. Hardware: Computer sy~tems, Network Interface Cards (NIC), cables, modems, hubs, satellites, etc. ,. { Software: Any software, which supports networking features, like Unix, Linux, Windows -NT, etc. so that data.can be sent or received. Protocol: Protocol could be defined as a standard procedure for regulating data transmission between computers. It specifies a way to identify the destination and source computers and establish a connection 'between them to receive or send data. For example, TCP/IP or UDP protocols help to divide data into small packets of several bytes, insert the packets into frames, and then send those frames to the destination computer over the network. Protocol is the underlying feature of the software used on the network. o o o What Comprises the Internet? Internet could- be defined as the network of all the computers eXisting on the ea,rth. Not only individual computers but also a network of computers can be connected into the Internet. For example, a company may have 100 computers, all connected by the cable. Now, this local network can be directly connected to the Internet, so that it becomes a part of the Internet. So, Internet is also sometimes defined as a global network of all networks. Going back to the history ofInternet in 1969, DoD (Department of Defense), which is a US military defense department, got 4 computers which they connected with a cable. These 4 computers were connected by a cable and Unix was installed on them. This is the first network on the earth, which is also called ARPANET (Advanced Research Project Agency Network). Figure 1.2 shows how computers were connected in an ARPANET. . ,. = Figure 1.2 ARPANET, the first network Later on, NSFNET (National Science Foundation (NSF)) encouraged individual users to get connected into this network. Any user can simply connect his computer into this network by using a cable. But the first problem faced by the users is purchasing and installing the cables. For example, imagine how much lengthy cable is needed if a person in India wants to connect his computer to this network. So they thought of an alternative. If already available cables are used, this problem will be' resolved. By that time, telephone networks are Widely available. Hence, telephone companies like AT&T,. Hyundai, British Telecom, etc. came forward and offered their networks for use. Now, the problem of connecting personal computers with a network is solved. People who want to connect to the network can simply sit in their homes and connect their computers to the telephone jack. Thus, more and more computers have started becoming a part of this network and the network has grown rapidly. Today, this network has trillions of computers
- 22. All about Networks L1.. connected with each other. Thus, it became the biggest network on the eartli. This network is called Internet. A network of computers within an organization is called Intranet .'n external network connecting an organization's network with that of another organization is called Extranei. In other words, we can take Extranet as a network outside an organization connecting it to other organizations' network. Similarly, an organization may use the services of a third party private network to communicate with outside networks. This third party private network is called VAN (Value Added Network). Now, let us try to understand the concept of Intranet and ExtFanet with the help of a figure. In Figure 1.3, you can notice that the network within an organization '~ed Intranet and that connecting the networks of two organizations is known as an Extranet. Organization 1 Organization 2 'Figure 1.3 Intranet and Extranet How does Internet Function? 'pke any network, Internet also requires certain hardware, software, and- protocols to perf0rJ!l its ft.'nctions. For example, hardware like computer systems, cables, hubs, routers, satellites, etc. are needed to connect different computers with each other. The computer, which is connected to Internet Service Provider's (ISP) computer is called client and the ISP's computer is called server. Other than ISP servers, many other servers are maintained and used privately by some organizations. Currently, millions of servers are available on Internet. Some servers focus on a single.area like maintaining employees' attendance in a company or scheduling the jobs for the employees of different branches. Such servers are called Application servers. Some servers provide services purely related to Internet, for example, maintaining the Websites and communicating with clients on Internet. Such servers are called Web servers. " A client machine and a server machine on Internet also need software. The software that is installed on an Internet client is called Web browser. Popular Web browsers are Internet Explorer,Netscape Navigator, Mozilla Firefox, Mosaic, etc. The software that is installed on an Internet server machine is called Web server. There are several Web servers, like IIS (Internet Information Server), Web logic, Web dynamics, Apache, JBoss, etc. Apart'from software, protocols are also used on Internet. The most widely used protocol on Internet is http, which stands for hypertext transfer protocol. http is responsible for displaying the html pages (or Web pages) on your client machine when you browse Internet. When you download a file from Internet to your client machine, you are using ftp (file trapsfer protocol). When you send mails, SMTP (Simple Mail Transfer Protocol) is used, and while receiving mails POP (Post Office Protocol) is used. . Which is the most widely used protocol on Internet? Hypertext transfer protocol (http) is the most widely used protocol on Internet. The text on Internet is sent or received from one machine to another using this protocol only. Software Development for Internet Suppose we are writing a C program with the name x :c. This means x. c fIle contains source code. When we compile this program, we get x. obj fIle that contains machine language code, which is
- 23. .±.JChapter 1 just equal to the source code in x. c me. For example, this x. obj me contains the first statement to -include a header me, like <stdio. h>. When we run the program, C compiler goes to the C standard library (it is found generally,Juo-tclib)' and searches for the header file <stdio. h> there:,When the header file is found, C compiler copies the ~ntire code (this code will be in machine language format) from the header file int,9'-the C program. So,:ifyou writeaC program of 10 lines and the <stdio.h> file contains 200 line~ then the total size of the file will be 210 lines. This file is also called x. exe file. This file is a full-fledged. file that contains the entire prof7'l.m in machine language instru,ctions. These instructions-,are understandable to the microprocessor. So it executes them and gives the results. Figur~shows how the source code in a C program is converted to machine language instruction~beforebeing executed by the compiler. . , There are several microprocessors developed by many companies, for example, Intel Corporation. Every microprocessor can recognize a group of instructions called the Instrnction set of that -microprocessor. So the instructions recognized by Pentium processor may not be understandable to the Celeron and similarly the instructions of Celeron may not be understandable by Spark processor. If we generate x .'exe file on a computer with Pentium processor, then that x. exe file contains machine laIlguage instructiohs understandable to Pentium only. If we tryeto execute this x . exe file on another computer with Spark processor, it may not be able to 'execute the instructions of x. exe file. The reason is Spark processor cannot understand th~ Pentium processor instructions, which are in x. exe. Figure 1.4 Execution of a C program D = Program output Executable code Object code C program source code Similarly, develop x . exe file using an operating system like DOS. Then 'copy this x. exe into other' . operating system like UNIX. Now, try to execute the x. ex€! file on UNIX. You will see that you cannot! The reason for this is that every operating system stores the ·data and instructions iI:l different formats. For example, the instruction for addition of two values may be stored by DOS as: add a, b; whefeas the same instruction may be stored by UNIX as: a add b. So, if we try to execute add a, b instruction in UNIX, it cannot un1erstand it since its format is different from what it is expecting. This is 'the reason, why we cannot execute the same x. exe me' in different operating systems. There is a lot about instruction formats. The example that we have taken is only for illustration purpose. What does it mean? If we created an . exe file in C or C++ on X processor and Y operating system, then we can execute it on X processor and Y operating system only. If the processor is changed or ' the operating system is changed, then it is not possible to execute the same code. This means C or C++ programs are executable only on the computer system that has X processor .and Y operating system, where they have been developed. They cannot be executed on a different configUration. So they are called system dependent programs. Hence, C or' C++ languages are also called system dependent or platform dependent languages. Now, let us come back to Internet. As we know that Internet is a global network of all the computers existing on the earth and anyone can connect hisfI:er computer to this network. So there will be different types of compu'~ers with different processors and different operating systems existing on Internet. It is completely heterogeneous. So, if a software is developed using C/C++ like languages, that software can be distributed on the Internet and people can download the . exe files, but they cannot run those files because of their system dependency. So C/C++ is not suitable for developing
- 24. I All about Networks l.l. .software for Internet. We need a language, which is completely system independent so that it can run on any system on Internet. And that is Java! How Java is suitable for Internet? In Java, if we write a program, it is stored with an extension . java. Let us create a program, say x. java. It contains java source code stat~ments. Now, the: first step is to compile this x. java program. To do· that, Java compiler first translates the x. java program into x. class file. What will be there in x. class file? Java pe:ople coined a group of instructions to express any operation. These instru~tions are called byte code instructions because the size of each instruction is 1 byte (=8 bits) exactly. There are a -fixed fiu~er of byte code instructions, around 200. Any java program can be rewritten using these'Iew byte code instructions. That file is called x. class. So, we can say that a x. class file containssource code equivalent to byte code. ". But the microprocessor cannot understand byte code instructions, neither can it execdte them. Then, these byte code instructions are meant for whom? They are for JVM (Java Virtual Ma2h---n'i~ These byte code instructions are understandable by JVM, which is a program written to understand the byte code instructions and convert them into machine code. JVM's role is very crucial in a way that it has to first identify the operating system and processor used in the computer system and then convert the byte code instructions in an understandable format for that particular processor and operating system. Remember, JVM is not a machine-it is a program! JVM program is freely available on Internet and can be downloaded for use in a few minutes. Figure 1.5 shows how a java- source code passes through various stages before being executed by the compiler. - ---:::::::. o = Java program source code. Byte code JliM converts byte - Program output code into machine code i Figure I.S Execution of a Java program . So, if -ive write x. java program on a computer using Pentium processor and compile it, the compiler will produce x. class containing byte code instructions. - These byte code instructions are given to JVM. Now JVM understands that we are using Pentium processor in our system, so -it converts byte code into-machine code, which is understandable by the Pentium processor. So the processor executes it and displays the results. Similarly, JVM understands the operating-system used in the computer and accordingly it forms the instructions, so there will not be any problem for the operating system to understand these instructions. Now, if we send the same x. class file to another computer system with a different processor, say Spark processor, then the JVM in that system will convert these byte code instructions to machine code understandable by the Spark processor. So Spark processor can execute those instructions and display the results. In this way, we can execute the . cl-ass file on any computer system with- any processor and any operating system-provided JVM is available. Remember byte code is system independent. It can be created on any computer using those predefined 200 instructions only. But JVM is system dependent, since it has 10 interact with the processor and operating system of the computer. This is the reason behind several flavors of JVM available on Internet. If we are using Windows, then we should download only Windows version of JVM and if we are using Linux, then we should use only Linux version of JVM. So, if we write a· . java program on X processor and Y -operating system, then that program is executable on any other computer system with any processor and operating system. This means java programs are system independent or platform independent. That's why Java is called a system independent programming language. On Internet, different computer systems with different processors and different operating systems are available, but still Java programs will run on any system and produce the same results on all the systems. If we develop a software using Java, the. class files can be downloaded from Interne
- 25. ~ Chapter 1 and can be executed on any other computer system without any problem. Hence, Java is a suitable programming language for-software development on Internet. What is the difference· between an executable file and a .class file? .exe file- contains machine language instructions for the microprocessor and is system dependent. .class file contains byte code instructions for the JVM and is system independent. .-/- - . Since Inteniet is a public network, everyone can connect their computers into Internet and this leads to several security problems for data. Suppose, we are sending an email to a friend. Now, this mail will' go through millions of servers on Internet before reaching the destination computer. In between, anybody can open the mail and see the data of the mail. Thus, we can say that data sent over' Internet is' susceptible -to many kinds of security threats. Let us discuss some of the major -~curityproblems for data.on Internet along with their solutions: o Eavesdropping: This means reading others' data illegally on Internet. For example, opening others' emails and reading them comes into this category. The solution for thIS problem is: encryption and decryption. Converting the data into an unre~dable format is called encryption and getting back the original data from the encrypted format is called decryption. When sending the email, we can encrypt the data and send it. If any third person opens it, he cannot read it because it is in an unreadable format. While encrypting the data, we use a password called key. Only the person who knows that key can decrypt it and read it. This key is known to our friend to whom the email is sent, so that only he can open it and read it. Encryption and decryption can be done using Java technology. o Tampering: This is another problem on Internet. Not only reading others' data but also modifying it is called tampering. Encryption and decryption is the solution for this problem arso. If we encrypt the data, a third person cannot read it so he cannot modify it also. o Impersonation: A per-son disguising himself as another person on Internet is called impersonation. _ Many people hide their original identity and act as somebody else to make transactions. The solution for this problem is digital signature. Digital signature is a file that contains personal identification information in an encrypted format. Storing the personal information in digital signature and sending this information along with the email assures the receiver of the identity of the sender. Digital signature can be created using Java technology,. o Virus: Virus represents a program that can cause harm to the data, software, and hardware of a computer system. Most of the viruses spread with . exe,. doc, image (. gif, . jpg), audio, and video mes(.mpg, .avi, .mp3). Virus cannot spread with a .txt me (example, the.me created in Notepad). In Java, we create. class mes, which are similar to . txt mes and hence there is no chance of virus affecting these meso Even if somebody intentionally tries to incorporate the virus code into a , class file, JVM can verify its presence before running the program and, if found, can abort the .class file's execution. From ,the above discussion, we can say that Java is the language, which can eliminate the above security problems that often occur on Internet. This is another reason why Java is sought after for developing software meant for Internet. '~.-"Q:~ Why Java is suitable for Internet? (Java is suitable for Internet because of two main reasons. 1) It is system independent and hence its -programs can run on any type of computer system available on Internet. 2) It eliminates a lot of security problems for data on Internet. . Conclusion By now, you must have gathered information about networks, the Internet, and how Java is suitable for the Internet.
- 26. CHAPTER INTRODUCTION TO JAVA t B efore starting to learn Java, let us plunge into its history and see how the language originated. In 1990, Sun Microsystems Inc. (US) has conceived a project to develop software for consumer electronic devices that could be controlled by a remote. This project was called Stealth Project but later its name was changed to Green Project In January of 1991, Bill Joy, James Gosling, Mike Sheradin, Patrick Naughton, and several others met in Aspen, Colorado to discuss this' project. Mike Sheradin was to focus on business development; Patrick Naughton was to begin work on the graphics system; and James Gosling was to ide.ntify the proper programming language for the project. Gosling thought C and C++ could be used to develop the project. But the problem he faced with them is that they were system dependent 'languages and hence could not be used on various processors, which the electronic devices might use. So he started developing a ne"", language, which was completely system independenf. Th'is language was initially called Oak. Since this name was registered by some other company, later it was changed to Java. ' Why the name Java? James Gosling and his team members were consuming a lot of tea while developing this language. They felt that they were able to develop a better language because of the good quality tea they had consumed. So the tea also had its own role in developing this language and hence, they fIxed the name for the language as Java. Thus, the symbol for Java is tea cup and saucer. B)llSeptem1:>er of 1994, Naughton and Jonathan Payne started writing WebRunner-a Java"based Web browser, which was later renamed as HotJava. By October 1994, HotJava was stable and was demonstrated to Sun executives. HotJava was the fIrst browser, having the capabilities of executing applets, which are programs designed to run dynamically on Internet: This time, Java's potential in the context of the World Wide Web was recognized. Sun formally announced Java and HotJava at SunWorld conference in 1995. Soon after, Netscape Inc. 'announced that it would incorporate Java support in its browser Netscape Navigator.- Later, Microsoft also announced that they would support Java in their Internet Explorer Web browser, further solidifying Java's role in the World Wide Web. On January 23rd 1996, JDK 1.0 version was released. Today more than 4 million developers use Java and more than 1.75 billion devices run· Java. Thus, Java pervaded the world. Features of Java Apart from being a system independent language, there are other reasons too for the immense popularity of thi-s language. Let us have a look at some of its features.
- 27. .!..JChapter 2 o Simple: Java is a simple programming language. Rather than saying that this is the feature of Java, we can say that this is the design ,aim of Java. When 'Java is developed, they wanted it to be simple because it has to work on electronic devices, where less memory is available.' Now,_ the question is how Java is made simple? First of all, the difficultconcepts of C and C++ have been omitted in Java. For example, the concept of pointers-which is very difficult for both learners and programmers-has been completely eliminated from Java. Next, 'JavaSoft (the team who develoPed Java is called with this name) people maintained the same syntax of C and C++ in Java, so that a programmer who knows C or C++ will find Java already familiar. Figure 2.1 Class and object Why pointers are eliminated from Java? 1. Pointers lead to confusion for a programmer. 2. Pointers may crash a program easily, for example, when we add two pointers, the program, crashes immediately. The same thing could also happen when we forgot to free the memory allotted to a variable and reallot it to some other variable. 3. Pointers break security. Using pointers, harmful programs like Virus and other hacking programs can be developed. Because ofthe above reasons, pointers have been'eliminated from Java. o Object-oriented: Java is an object,oriented programming language. This means Java programs use objects and classes. What is an object? An object is anything that really exists in the world and can be distinguished from others. Everything that we see physically will corne into this definition, for example, .everyohuman being, a book, a tree, and so on. . Now, every object has properties and exhibits certain behavior. Let us try to illustrate this point by taking an example of'a dog. It got properties like name, height; color, 'age, etc. These properties are represented by variables. Now, the- object dog will have some actions like running, barking, eating, etc. These_~actions are represented by variou~ methods (functions) in our programming. In programming, VaflOUS tasks are done by methods only. So, we can conclude that objects contain variables and methods. . A group of objects exhibiting same behavior (properties + actions) will come under the saI1!.e group' called a class. A class represents a group name given to several objects. For example, take the clogs: Pinky, Nancy, Tom, and Subbu. All these four dogs exhibit same behavior and hertce belong to the same group, called dog. So dog is the class name, which contains four objects.Jn other words, we could define a class as a model or a blueprint for creating the objects. We write the charaCteristics of the objects in the class: 'dog'. This means, a class can be used as a model in creation of objects. So, Just like objects, a class also contains properties and actions, i.e. variables and methods (Figure 2.1). properties· vars actions· methods ruoO bark{) eatO Tom _1 foot brown 5_years object Tom actions· methods properties: vars - running barking eating height-", color _ age class: Dog
- 28. Introduction to Java L.2. We can use a class as a model for creating objects. To write a class, we· can write all the characteristics of objects which_should follow the class. These characteristics will guide us to create the objects. A class and its objects are_almost the same with the difference that a class does not exist physically, while an object does. For example, if we say dog; it forms a picture into our mind with 4 legs, 2 ears, some length and height. This picture in our mind i1'Lc1ass. If we.. tally this picture with the physical things around us, we can find Tom living in our house is satisfying these qualities. So Tom, which physically exists, is an object and not a class. Let us take another example. Flower is a class but if we take Rose, Lily, Jasmine - th~y are all objects of flower class. The class flower does not exist physically but its objects, like Rose, Lily, Jasmine exist physically. What is the difference between a function and.a m€}thod? A method is a function that is written in a class. We do not haile functions in Java; instead we-'have methods. This means whenever a function is written in Java, it should be written inside the class only. But if we take C++, we can write the functions inside as well as outside the class. So in C++, they are called member functions and not methods. - ' - Since Java is a purely object-oriented'prograrriming language, in order to write a program in Java, we need atleast a Class or an object. This is the reason why in every Java program we write atleast one class. C++ is not a purely object-oriented language, since it is possible to write programs in C++ without using a class or an object. ' - o Distributed: Information is distributed on various computers on a network. Ysing Java, we can write prQgrams, which capture information and distribute it to the clients. This is possible because Java can handle the protocols like TCP/IP and UDP. [J Robust: Robust means -strong. Java programs are strong and they don't crash easily like a C or C++ program. There arc two reasons -for this. Firstly, Java has got excellent inbuilt exception handling features. An exception is an error that occurs at run time. If an exception occurs, the program terminates abruptly giving rise to problems like loss of data. Overcoming such problems is called.'exception handling. This means that even though an exception occurs in a Java program, no harm will happen. - - .. Another reason, why Java is robust lies in its memory management features. Most of the C and C++ prOgrams crash in the' middle because of:not allocating sufficient memory or forgetting the memory to be freed in a program. Such problems will not occur in Java because the user need not-allocate. or deallocate the memory in Java. Everything will be taken care of byJVM only. For exa.rnple, JVM will allocate the necessary memory needed by a Java program. Which part of JVM will allocate the memory for a Java program? Class loader subsystem of JVM will allocate the necessary memory needed by the Java prpgram. Similarly, JVM is also capable of deallocating the memory when it is nut used. Suppose a variable or an object is created in memory and is not used. Then after some time, it is automatically removed by garbage collector of JVM. Garbage collector is a form of memory management that checks the memory from time to time and marks the variables or objects not used by the program, automatically. After repeatedly identifying the same variable or object, garbage collector confirms that -the variable or object is not used and hence can be deleted.
- 29. .2EJChapter 2 Which algorithm is used by garbage collector to remove the unused variables or objects from memory? Garbage collector uses many algorithms but the most commonly used algorithm is mark and sweep. How can you call the garbage collector? Garbage collector is automatically invoked when the program is being run. It can be also called by calling gc() method of Runtime class or System class in Java. o Secure.: Security problems like eavesdropping, tampering, impersonation, and virus threats can be eliminated or minimized by using Java on Internet. o System independence: Java's byte code is not machine dependent. It can be run on any machine with anycprocessor and any operating system. o Portability: If a program yields the same result on every machine, then that program is called . portable. Java programs are portable. This is the result of Java's System independence nature. o Interpreted: Java programs are compiled to generate the byte code. This byte code can be downloaded and interpreted by the interpreter in JVM. If we take any other language, only an interpreter or a compiler is used fo execute the programs. But in Java., we use .both compiler and interpreter for the execution. o High Performance: The-problem with interpreter inside the JVM is that it is slow. Because of this, Java programs used to run slow. To overcome this problem, along with the interpreter, JavaSoft people have introduced JIT (Just In Time) compiler, which enhances the speed of' execution. So now in JVM, both interpreter and JIT compiler work together to run the program. o Multithreaded: A thread represents an individual process to execute a group of statements. JVM uses several threads to execute different blocks of code. Creating multiple threads is called 'multithreaded'. o Scalability: Java platform can be implemented on a wide range of computers with varying levels of resources-from embedded devices to mainframe computers. This is possible because Java is compact and platform independent. - ~. o Dynamic: Before the development of Java, only static text used to be displayed-in the browser. But when James Gosling dernonstrated an animated atomic molecule where the rays are moving and stretching, the view~rs were dumbstruck. This animation was done using an applet program, which are the dynamically intetacting programs on Internet. The Java Virtual Machine Java Virtual Machine (JVM) is the heart of entire Java program execution process. It is responsible for taking the . class file and converting each byte code instruction into the machine language instruction that can be executed by the microprocessor. Figure 2.2 shows the architecture of Java Virtual Machine.
- 30. Method area Classfile_ Class loader subsystem I Java stacks pc registers Introduction to Java l!!.. Native method stacks t Interpreter Execution I 'engine Runtime data areas JIT compiler ~ .I Operating System Figure 2.2 Components in JVM architecture First of all, the . java program'is converted into a . clas s me consisting of byte code instructions by the java compiler. Remember, this java compiler is outside the JVM: Now this. class file is given to the JVM. In JVM, there is a module (or program) called class loader sub system, which performs the following functions: . o First of all, it loads the. class fIle into memory. o Then it verifIes whether all byte code instructions are proper or not. If it fmds any instruction suspicious, the execution is rejected immediately. o If the byte instructions are proper, then it allocates necessary memory.to execute the program. This memory is divided into 5 parts, called run time data areas, which contain the data and results while running the program. These areas are as follows: o Method area: Method area is the memory block,. which stores the class code,. code of the variables, and code of the methods in the Java program. (Method means functions written in a class) o Heap: This is the area where objects are created. Whenever JVM loads a class, a method and a heap area are immediately created in it. o Java Stacks: Method code is stored on Method area.. But while running a method, it needs some more memory to store the data and results. This memory is allotted on Java stacks.. So, Java stacks are memory areas where Java methods are executed. While executing methods, a separate frame will be created in the Java stack, where the method is executed. JVM uses a separate thread (or process) to execute each method. . o PC (Program Counter) registers: These are the registers (memory areas), which contain memory address of the instructions of the methods. If t1:J.ere are 3 methods, 3 PC registers will be used to track the instructions of the methods. . o Native method stacks: Java methods are executed on Java stacks. Similarly, native methods (for example CjC++ functions) are executed on Native method stacks. To execute the native methods, generally native method libraries (for example CjC++ header mes) are required. These header mes are located and connected to JVM by aprogram, called Native method interface.
- 31. ~ Chapter 2 Execution engine contains interpreter and JIT (Just In Time) compiler, which are responsible for converting the byte code instructions into machine code so that the processor will execute them. Most of the JVM implementations use both the interpreter and JIT compiler simultaneously to convert the byte code. This technique is also called adaptive optimizer. Generally, any language (like C/C++, Fortran, COBOL, etc.) will use either an interpreter or a compiler to translate the source code into a machine code. But in JVM, we got interpreter and JIT compiler both working at the same time on byte code to translate it into machine code. Now, the main question is why both are needed and how both work simultaneously? To understand this, let us take some sample code. Assume these are byte code instructions: When, the-interpreter starts execution from IS,I instruction, it converts print a; into machine code and gives it to the microprocessor. For this, say the interpreter has taken 2 nanoseconds time. The processor takes it, executes it, and the value of a is displayed. Now, the interpreter comes back into memory and reads the 2nd instruction print b; To convert this into machine code, it takes another 2 nanoseconds. Then the instruction is given to the processor and it executes it. ~ Next, the interpreter comes to the 3rd instruction, which is a looping statement print a; This should be done 10 times and this is known to the interpreter. Hence, the first time it converts print a into machine code. It takes 2·nanoseconds for this. Mter giving this instruction to the processor, it comes back tomemoxy and reads the print a instruction the 2nd time and converts it to machine code. This will tS-ke another 2 nanoseconds. This will be given to the processor and the interpreter. comes back and reads print a again and converts it 3rd time taking another 2 nanoseconds. Like this, the interpreter will convert the print a instruction for 10 times, consuming a total of 10 x 2 = 20 nanoseconds. This procedure is not efficient in terms of time. That is the reason why JVM does not allocate this code to the interpreter. It allots this code to the JIT compiler.' . Let us see how the JIT compiler will execute the looping instruction. First of all, the JIT compiler reads the print a instruction and converts that into machine code. For this, say, it is taking 2 nanoseconds. Then the JIT compiler allots a block of memory and pushes this machine code instruction into that memory. For this,say, it is taking another 2 nanoseconds. This means JIT compiler has taken a total of 4 nanoseconds. Now, the processor will fetch this instruction from memory and executes it 10 times. Just observe that the JIT compiler has taken only 4 nanoseconds for execution, whereas to execute the same loop the interpreter needs 20 nanoseconds. Thus, JIT compiler increases the speed of execution. Recognize that the first two instructions will not be allotted to JIT compiler by the JVM. The reason is clear. Here it takes 4 nanoseconds to convert each instruction, whereas the interpreter actually took only 2 nanoseconds. Mter loading the . class code into memory, JVM first of all identifies which code is to be left to interpreter and which one to JIT compiler so that the performance is better. The blocks of code allocated for JIT compiler are also called'hotspots. Thus, both the interpreter and JIT compiler will work simultaneously to translate the byte code into machine code. What is JIT compiler? JIT compiler is the part of JVM which increases tbe speed of execution of a Javaprogram.
- 32. Introduction to Java ~ Differences between c++ andJava: By the way, C++ is also an object-oriented programming language, just like Java. But there are some important feature-wise differences, between C++ and Java. Let us have a glance at them' in Table 2.1. Table 2.1 C++ Java C++ is not a purely object,-oriented ·~~~~n~~~~;oJ· '~o~i using a class er an object. Pointers are available in C++. Multiple Inheritance feature is available in C++. . Ope.rator overloading is available in C++. It>4s not available in Java. and header files are There are constructors and destructors in C++. Parts of Java Only constructors are there in Java. NCLdestructors are available in this language. Sun Microsystems Inc. has divid~d Java into 3 parts-Java SE, Java EE, and Java ME. Let us . discuss them in brief here: o Java SE: It is the Java Standard .Edition that contains basic core Java classes. This edition is used to develop standard appletsand applications. o Java EE: It is the Java Enterprise Edition and it contains classes that are beyond Java SE. In fact, we need Java SE in order to use many of the classes in Java EE. Java EE mainly concentrates on providing business solutions on a network. o Java ME: It stands for~Java Micro Edition. Java ME is for developers who develop code. for portable devices, such as a PDA or a cellular phone. Code on these devices needs to be small in siz€ and should ~ake less memory.
- 33. .2!JChapter 2 Java software can be downloaded from the Sun Microsystems site: http://java.sun.comljavase/downloads/index.jsp Conclusion . In this chapter, you have learned the features of the Java. and got familiar with the JVM architecture along with part of ~ava. By now, you must have got a glimpse of Java. Along with all thi~,we have also compared the C++ with Java. .
- 34. FIRST STEP TOWARDS JAVA PROGRAMMING CHAPTER W henever we. want to write a ·program, .w~ ShO.Uld first think about. writing comme~ts. What are comments? Comments are descnptlOn about the features of a program. ThIS means that whatever we write in aprogram should be described using comments. Why should we write comments? When we write comments, we can understand what the program is doing as well as it helps others to easily follow our code. This means readability and understandability of a program will be more. If a program is understandable, then only can it be usable in a software. If other members of the software development team cannot understand our program, then they may not be able to use it in the project and will reject it. So writing comments is compulsory in any program. Remember, it is a good programming habit. There are three types of comments in Java-single line, multi line, and Java documentation. Let us discuss all of them here: o Single line comments: These comments are for marking a SL'1gle line as a comment. These comments start with double slash symbol / / and after this, whatever is written till the end of the line is taken as a comment. For example, Tn o Multi-line comments: These comments are used for representing several lines as comments. These comments start with / * and end with */. In between / * and */, whatever is written is treated as a comment. For example, o Java documentation comments: These comments start vvith / ** and ehd with */. These comments are used to provide description for every feature in a Java program. This description proves helpful in the creation of a .html file called API (Application Programming Interface) document: Java documentation comments should be used before every feature in the program as shown here: 7 ' cfescri ptl on class coce /"*.,d.escrd pti'on about a Method c de
- 35. ~ Chapter 3 API Document The API document generated from the. java program is similar to a helpflle where all the features are available with their descriptions. The user can refer to any feature in this file and get some knowledge regarding how he can use it in his program. To create anAPI document, we should use a special compiler called j avadoc compiler. Figure 3.1 shows the process of creation of an API document. API document class Classname description about class package Packagename description about package void rnethodname() description about method ---+ void methodnameO description about method method code; method code; class code; ,- description about method"" void methodnameO { } ,.. d_escription about method-' void mathodname() { Java program r*description about package"" , package Packagename; .e-description about dass*' class Classname { In u e<s 10. > What is an API document? An API document is a . h tml file that contains description of all the features of a software, a product, or a technology. API document is helpful for the user to understand. how to use the software or . technology. This means, a request is made to the C/C++ compiler to include the header file <s,tdio. h>. What is a header file? A header file is a file, which contains the code of functions that will be needed in a program. In other words, to be able to use any function in a program, we must first include the header file containing that function's code in our program. For example, <stdio. h> is the header Figure 3.1 API document creation Importing classes Suppose we are writing a C/C++ program, the frrstline of the program would generally be: Starting a Java program So let us shirt our first Java program with multi line comments:
- 36. First Steps towards Java Programming 17 me that contains functions, like printf (), scanf (), puts (), gets (), etc. So if we want to use any of these functions, we should include this header file in our CjC++ program. ' What happens when we include the header fIle? After we include the header fIle, the CjC++ compiler goes to the standard library (generally it is available in tcl lib) and searches for the ,header fIle there. When it finds the header fIle, it copies the entire header me content into the program where the #include statement is written. Thus, if we write a program of 10 lines; then after copying code from the header file, the program size may become, say, 510 lines. From where do these additional 500 lines are coming? They have been copied physically i,nto our program from the header fIle. Thus, our program size increases unnecessarily, wasting memory and processor ti~. . A similar but a more efficient mechanism, available in case of Java, is that of importing classes. First, we should decide which classes are 'needed in our program. Generally, programmers are interested in two things: o Using the classes by creating objects in them. o Using the methods (functi~ns) of the classes. In Java, methods are available in classes or interfaces. What is an interface? An interface is similar to a class that contains some methods. Of course, there is a lot of difference between an interface and a class, which we will discuss later. The main point to be kept in mind, at this stage, is that a class or an interface contains methods. A group of classes and interfaces are contained in a' package. A package is a kind of directory that contains a group of related Classes and interfaces and Java has several such packages.,in its library, Java library I Packages I Classes and interfaces I Methods If a programmer wants to use a class, then that class should be imported into his program. If he wants to use a method, then that corresponding class or interface should be imported into his program. In our first Java program, we are using two classes namely, System and String. These classes belong to a package called java .lang (here lang represents language). So tJ;i.ese two classes must be imported into our program, as shown below: Whenever We want to import several classes of the same package, we need not write several import statements, as shown above; instead, we can write a single statement as: mort "ava. an . . Here, * means all the classes and interfaces of that package, i.e. java. lang, are imported (made available) into our program. In import statement, the package name that we hav.e written acts like a reference to the JVM to search for the classes there. JVM will not copy any code from the classes or packages. On the other hand, when a class name or a method name is used, JVM goes to the Java library, executes the code there, comes back, and substitutes the result in that place of the program. Thus, the Java program size will not be increased.
- 37. ~ChaPter3 - What is the difference between#include and import statement? ,I #include directive makes the f:ompiler go to the C/C++ standard library and copy the code from 'the header files into the program. As a result, the program size increases, -thus wasting memory and processor's time. - import statement makes the JVM go to the Java standard library, execute the code there, and substitute the result into the program. Here, no code is copied and hence no waste of memory or pt:ocessor's time, So, import is an efficient mechanism than #include. Mter importing the classes into the program, the next step is to write a class, Since Java is purely an object-oriented programming language, we cannot write a Java program without having at least one class or object. So, it is mandatory that every Java program should have at least one class in it, How to write a class? We should use class keyword for this purpose and then write the class name. u51ic statlc Vela maln Strln ar 5 Next to main () method's name, we have written String args []. Before discussing the main () method, let us fIrst see how a method works, A method, gen~rally, performs two functions. D It can accept some data from outside D It can also return some result A class code starts with a { and ends with a }. We know that a class or an object contains variables and methods (functions), 'So we can create any number of variables and methods inside the class. This is our fIrst program, so we will create_ onlY.one method, i.e. compulsory, in it-main () method. Why should we write main {} method? Because, if main () method is not Wlitten in a Java program, JVM will not execute-it. main (} is the starting point for JVM to start execution of a Java program, r 5 i CSt 'n Let us take sqrt () method. This method is used to cal9ulate square root value -of a given number. So, at the time of calling sqrt n method, we should pass a number (e.g~ 16) for which we want to calculate square root, Then, it calcula_tes square root value and returns the result (e,g. 4) to us. Similarly, main () method also accepts some data from us, For example, it accepts a group of strings, which is also called a string type array, This array is String args [] , which is written along with the main n method as: I Here args [] is the array name and it is of String type. This means that it can store a group of strings, Remember, this array can also store a group of numbers but in the form of strings only. The- values passed to main () method are called arguments. These arguments are stored into args [] -array, so the name args [] is generally used for it. Amethod can return some result. If we want the method to return the result in form of an integer, then we should write int before the method name. Similarly, to get the result ill string form or as a single character, we can write string or char before it, respectively. If a method is not meant to return any value, then we should write void before that method's name. void means no value. main () method does not return any value, so void should be written before that method's name. A method is executed only when it is called, But, how to call a method? Methods are called using 2 steps in Java.
- 38. First Steps towards Java Programming l.2!. 1. Create an object to the class to which the method belongs. The syntax of creating the object is: I 2. Then the ~ethod should be called using the obj ectname .methodname () . Since main () method exists in the class First; to call main () method, we should first of all create an object to First class, something like this: Then call the main () method as: j.m i So, if we write the statement: - , ",side the main () method, then JVM will execute this statement and create the object. r class Fi rst { y looking at the code, we can understand that an object could be created ocly af!er callin~ the· main () method. But for calling the main·() method, fIrst of all we require an object. Now, how'is it possibl~ to cr~ate an object before callmg the main () method? So, ~e should- call the main·() method without creating an" object. Such met.hods are called static methods and should be declared as static. Static methods are the methods, which can be called and executed without creating the objects. Since we want to call main () method without using an object, we should declare main () method as static. Then, how is the main () method called and executed? The answer is by using the classname .methodname (). JVM calls main () method using its dass name as First .main () at the time of running the program. JVM is a program written by JavaSoft people (Java development team) and main () is the method written by us. Since, main () method should be available to the JVM, it should be declared as public. If we don't declare main () method as public, then. it doesn't make itself available to JVM and JVM cannot execute it: So, the main () method should always be written as shown here: If at all we want to make any changes, we can interchange public and static and write it as follows: (jl)] lC
- 39. Till now, according to our discussion, our Java program looks like this: '- 22.J Chapter 3 Or, we can use a different name for the string type array and write it as: [ args'[] is not written in main () method? When rnai n () method is written without S t r ing a rgs [J as: public static void main () the code will compile but JVM cannot run the c,Ode because it cannot recognize the main () method as the method from where it should start execution of the Java program. Remember JVM always looks for main () method with sti-ing type arr!!y as parameter. Our aim of writing this program is just to display a string "Welcome to Java". In Java, print () method is used to display something on the monitor. So, we can write it as: But this is not the correct way of calling a method in Java. A method should be called by using objectname .methodname (). So, to call print () method, we should create an object to the class to which print () method belongs. print () method belongs to PrintStream class. So, we should call print () method by creating an object to printStrea~class as: But as it is not possible to create the object to PrintStream class directly, an alternative is given to us, i.e. System. out. Here, System is the class nam~and 01l;t is a static variable in System class. out is called afield in System class. When we call this field, a PrintStream class object will be created internally. So, we can call the print () method as shown below: System. out gives the PrintStream class object. This object, by default, represents the standard output device, i.e. the monitor. So, the string "Welcome to Java" will be sent to the monitor. Now, let us see the final version of our Java program:
- 40. First Steps towards Java Programming ~ Program 1: To display a message. Output: Save the above program in a text editor like Notepad with the name First. java. Now, go to System prompt and compile it usingjavac compiler as: The compiler generates a fIle called First. class that contains byte code instructions. This fIle is executed by calling the JVM as: Then, We can see the result. We already discussed that JVM is a program. Which program is it? By observing the command java First, We can say that JVM is nothing but java.exe program. In fact, JVM is written in C language. Let us write another Java program to fmd the sum of two numbers. We start this program with a single line comment like this: Then we should import whatever classes and interfaces we want to use in our program. In this program, we will use two classes: Systemand String. These classes are available in the package java. lang. So, we should import these classes as: o a Here, * represents all the classes of java. lang package. This import statement acts like a reference for the JVM to search for classes when a particular class is used .in the program. After writing the import statement, we should write a class,. since it is compulsory to create at least one class in every Java program. Let us write the class as shown below:
- 41. ~ Chapter 3 We know that a class contains variables and methods. Even if we do not creste variables or methods, we should write at least one method, Le. main (). The purpose of writing the main() method is to make JVM execute the statements within it. Let us take ariexample: Here, main () method is declared as public, static, and void. public because it should be made available to JVM, which is another program; static because it should be called without using any object; -and void because it does not return any value. Also, after the method name, we write String args [] which is an array to store the values passed to main () method. These values passed to main () are called arguments. These values are stored in args [] array in the form of strings. Inside the main () method, let us write the code to fi..'1d the sum of two numbers. Observe the full program now: - Program 2: To find the sum of hvo numbers. numoers jjdisplay resul<t system.out.print(z); Output: In the above program, inside main () method, we write the first statement as: int x
- 42. r ) / First Steps towards Java Programming ~ Here x, y are called variables. A variable represeritsmemory location' to store data or values. We want to st()re 'integer immbers into x, y. So before t..~ese variables, we ,write into This int represents the type of data to be stored into the variables. It is also calle<i a data type. By writing int x, y, we are announcing the java compiler that we 'are going to store integer'type data into x, y variables. Remember, declaring the datatype is always required before using any variable. All data types available in Java are discussed in Chapter 4. After declaring the x, y variables as int data type, we have stored integer numbers into x, y as: I = represents storing the right hand side value into the left hand side variable. Thus, 10 is stored into x and 25 is stored into 'y'. So =is a symbol that represents assignment (or stor;;tge) operation. Such symbols are also called operators. All the operators available in Java will be discussed in Chapter.5. The next step is to find the sum of these values. For this purpose, we write: At the right hand side we got x+y, which performs the sum. Here + is call~d additio'n' operator. The result of this sum is stored into z, which we cteclared as another int type variable. Now, we should display the result usirig print () method as: Here, syste~ is a clas~ in java .lang package and out is a field in this class. When we'refer to System. out, it createsPrintStream object, which, by default, represents the standard output device, Le.fI!.onitor.' So, by writing System.out.pri'nt(z), we are passing z value to print() method, which displays that value on the monitor. So in the output, we can see the result as 35. , Formatting the Output In Program 2, we have used the foilowing statement to dispiay the result: This will display the result ,35 'on the monitor. But, this is not the proper way to display the results to the user'. When the user sees 35, he would be baffled as what is this I).umber 35? So, it is the duty of the programmer to prompt the user with a proper message, something like this: This is more clear and avoids any confusion for the user. How can we display the output in the above format? for this purpose, we should add a string "Sum of two numbers=" before the z value in the print () method: Here, we are using +to join the string "Sum of two numbers=" 'and the numeric variable Z. The 'reason is that the print () method cannot ·display more than one value. So if two values, like a string and a numeric value need to be displayed using a single print () method, we should combine them using a + operator. Now, the output will look like this:
- 43. r n 2 r wo nurn e wo numOePs roz o um S t m. t. r n "u 0 Sum 0 Please observe that we have used two print (.) methods and still we got the result in only one line. What does it mean? First print () method is displaying the string: !'Sum of twolnumbers" and keeping the cursor in the same line. Next print () me1:lJod is also showing its output in the same u 0 two number'S This will also give the correct result as: Here, the execution will start from the inner braces.. At left, we got x, which represents a number and at right we got y I which is also,a number. Since both are number-s, 'a<fcI1tion will be done by the + operator, thus giving a result 35. Then the result will be displayed like this: urn· 0 two nurn ers- To eliminate the above inner braces, we can use two print () methods like this: n ~f t "nu blIFS'"'''+ X-r~ So, how to get the correct result? By using another pair of simple braces inside the print () method, we can get the correct result. u 0 two nurn e 5 See the output is wrong. What is the reason? In the print () method's braces, from left to right, we got a string "Sum of two humbers=" and two numerit: variables x and y as shown below: Since left one is a string, the next value, i.e. of x is also converted into a string; thus the value of x, i.e. ~O will be treated as separate characters as 1 aIld 0 and are joined to the string. Thus, we get the output in the string form: The next variable value is 25. Since till now, at left we got a string, so this y value is also converted into a s~ring. Thus 2 and 5 are taken as separate characters and joined to the string, thus we get the result as: . which displays: We know that value of x is 10 and y is 25. Suppose, we use print () method to display directly x+y value in the place of z, we can write: 2!.JChapter 3
- 44. I II I I First Steps towards Java Programming 25 line adjacent to the previous string. To conclude, print () method displays the result and then keeps the cursor in the same line. Suppose, we want the result in two separate lines, then we can use println () methqd in the place of print () method as: This will display the result in two lines as: Sum 0 two num6ers p:cintln () is also a method belonging to PrintStream class. It throws the cursor to the next line a....'ter displaying the result. What is the difference between print () and println () method? Both methods are used to display the results on the monitor. print () method displays the resLilt and then retains the cursor In the same line, next to the end of the result. println () displays the result and then throws the cursor to the next line. . ...et us take the following statement: :his will display the output as shown below: Sum 0 two numBers 35 _ ow, suppose we want to display the result in two lines using only one println () method, what is -" e way? For this purpose, we can use a code n inside the string, as shown here: :his will display the result like this: m f wo u r :iris means n is throwing the cursor into the next line at that place. This is called backslash code escape sequence. Table 3.1 lists the noteworthy backslash codes with their meanings. "able 3.1 Backslash code Meaning Next line Backspace
- 45. Backslash code ~ Chapter 3 For example, observe the following statements: The above statements display the output as: Program 3: To understand the effect of print () and println () methods and the backslash codes. Output: By now, you must be finding Java to be very friendly. Conclusion In this chapter, we have learned about providing comments in the java program. We have also come across with API documents. While moving towards the end of the chapter we have come across with the creating a program in Java.
- 46. AMING NO DATA CHAPTER PES ONVENTIONS I n the previous chapter, we understood Java by writing a couple of programs. In those programs, you might have observed that sometimes we have used small letters and sometimes capital letters. For example, we have written the class System starting with a capital letter. You cannot ·te this class name as system or SYSTEM. Since Java is a case sensitive programmingJanguage, it =gnizes capital and small letters as different. So the programmer should take care of upper and er case whilt;. writing a program in Java. But how to know where to use which case-upper or er? For this purpose, certain conventions (rules) are followed by JavaSoft people while naming e variables, classes, methods, etc. These naming conventions should be followed by every ;rrograrrimer in his programs for maintaining uniformity and also for clarity of distinction betWeen .. erent elements of a program. These rules also reduce the possibility of any spelling mistakes ~e writing the nanies of variables, classes, etc. in the programs. For example, a Java program will ::ot compile, if main () method is written as: I e problem in the preceding statement is using capital P for public and capital Mfor main (). Such =:mrs can be eliminated if we follow the naming conventions. ing Conventions in Java _mning conventions specify the rules'to be followed by a Java programmer while writing the names packages, classes, methods, etc. Now, let us see some of the major naming conventions to be - owed in Java. A package represents a sub directory that contains a group of classes and interfaces. Names of packages in Java are written in small letters as: .e h A class is a model for creating objects. A class specifies the properties and actions of objects. An interface is also similar to a class. Each word of class names and interface names start with a capital letter as:
- 47. ~ChaPter4 o A class and an interface contain methods and variables. The first word of a method name is in small letters; then from second word onwards, each new word starts with a capital letter as shown here: o The naming convention for variables names is same as that for methods as given here: 1!",,---,,-'II'o;_. _ Now, the question that is commonly asked is that if same rule is applied for both variables and methods, how can we distinguish between them? The answer is that since a method's name ends with· a pair of simple braces 0, it can be distingUished easily from a variable whose name will not have any braces. o Constants represent fixed values that cannot be altered. For example, PI is a constant whose value is 22/7 or 3 . 14159, which is fixed. Such constants should be written by using all capital letters as shown here: Here, BOLD is a constant in Font class. This is the way most of the inbuilt constants in Java are referenced. <. o All keywords should be written by using all small letters as follows:. Data Types in Java We know we need variables to store the data. Internally, a vanable represents a memory locatiOl which holds data. When we want to use a variable-in a program, we should first declare it as: Here, we are declaring that x is a variable, which can store int (integer) type data. This means in is representing the nature of data to be stored into x. int is also called a data type. For exampl( x can store an integer number like 125 as:
- 48. I lin as I ose ital are ion Naming Conventions and Data Types I 2 , x is a variable and = represents that the value 125 is stored into x. This value 125 stored into also called literal. There are various data types and literals defined in Java, which we will be ssing in this chapter. er Data Types data types represent integer numbers, Le. numbers without any fractional parts or decimal IS. For example, 125, -225678, 0, 1022, etc. come under this category. Integer data types are sub divided into byte, short, int, and long types. Table 4.1 lists the data types. 4.1 , type Memory size Minimum and Maximum values '" .. :>t. :!-::e 1 by.t.e -128 to +127 ><ll m -- yt 2 bytes -32768 to +32767 - 'iii 4 byte~ if. ~i;jls .. ."l:. ,~ @ii ':'; -- -2'14748364~tq;.Ji~14~48;3M7",~ ".I!ilo'!' - '. 'R...• 01' :.::, 9 8 bytes -9223372036854775808 to +9223372036854775807 us try to understand this through an example given here: teo~ ~ preceding statement, we are declaring byte data type for the variable rno and the value 10, is stored into rno. byte represents any value between -128 to +127. _:-; x=150L; -~, _50 is stored into x, which is declared as long type. Notice the L at the end of the statement. ," L is not there, then JVM allots only 2 bytes of memory to x as against the usual 8 bytes ory that should be allotted to a long type. The reason for this is that 2 bytes are sufficient to the value 150. But if we attach I or L at the end of the value as shown in the preceding Ie, then JVM will consider it as a long value and will allot-8 bytes to it. Data Types data types are useful to represent numbers with decimal point. For example, 3.14, 0.0012, -_::L 11, etc. are called floating point numbers. These are again classified as fl.oat (single . 'on floating point number) and double (double precision floating point number). The nce exists essentially in the number of digits, they can represent accurately after the decimal ~ This accuracy is also called precision. Table 4.2 depicts the size of' float and double. int :lIe, =:mble 8 bytes -1.8e308 to -4.ge-324 for negative values and 4.ge-324 to 1.8e308 for positive values
- 49. .22.JChapter 4 What is the difference between float and double? Floa t can represent up to 7 digits accurately after decimal point, whereas daubl e can represent up to 15 digits accurately after decimal point. Let us now look at an example given here: float i 3.'D12}i'; Here, the variable pi is containing the value 3 .142. I~ F is not written at the end, then JVM ~ould have allotted 8 bytes assuming the value to be double. The reason for this is that in float and double data types, the default is taken as double. By attaching F or f, we can ask the JVM to consider it as a float value and allot only 4 bytes. double distance=1.98e8; Here,e or E represents X 10 to the power. Hence, 1. 98e8 means 1. 98X108. This is also called scientific notation of re~resentingnumbers. Character Data Type This data type represents a single character like a, P, &, *, etc. Table 4.3 shows char data type details. Table 4.3 Data type Memory size Minimum and Maximum values Char 'II .." 2 bytes ;i't oto 65535 ."F ~ .,"1 Here is an example of character data type: cfla:f en ~X" Here, we are storing the single character 'x' into the variable ch. Here, 'X' is also called characte7 literal. WHenever character literals are written, they should be enclosed inside the single quotes. By observing the minimum and maximum values in the table earlier, we shall get a doubt regarding why the range is expressed in integer numbers (0 to 65535). We know that all the characters on the keyboard are translated into integer values called ASCII (American Standard Code for Information Interchange), which is a standard maintained by every keyboard manufacturer. The processOI recognizes the character uniquely from its ASCII value. Hence, let us understand the' range mentioned in the table is nothing but the ASCII value range only. The ASCII value range, from 0 to 65535, given in the table can uniquely represent a total of 6553E characters. This means a total of 65536 distinct characters can be recognized by Java. But we nevel use these many characters since our keyboard contains English alphabets and some othe] characters whose total does not exceed 256. This means 1 byte is s'Ufficient to represent all th< available characters of the keyboard. Then why 2" bytes are used to represent the char data type ir Java? JavaSoft people wanted to provide a facility to include characters not only from English but alS( from all other human languages to be used in Java programs. This will enable the programmers t( write and execute a Java program in any language, which becomes an advantage on Internet. Thi1 system is also called Unicode system. Unicode uses 2 bytes so that any character from any languagl can be encoded successfully.
- 50. llid nd to led pe er ~e 6 ~r ~r :e n o o s e Naming Conventions and Data Types l1!.. What is a Unicode system? Unicode system is an encoding standard that provides a unique number for every character, no matter what the platform, program, or language is. Unicode uses 2 bytes to represent a single character. String Data Types A String represents a group of characters, like New Delhi, AP123, etc. The simplest way to create a String is by storing a group of characters into a String type variable as: ri tr Now, the String type variable str contains "New Delhi". Note that any string written directly in a program should be enclosed by using double quotes. There is a class with the name String in Java, where several methods are provided to perform different operations on strings. Any string is considered as an object of String class. But in CjC++, a string is considered as a character array containing some characters where the last character would be 0. This is not valid in Java, since in Java, we got strings and character arrays both separately. . Now the question arises that if String is a cla~s, why are we taking it as a data type? The answer is that every class is a data type and is also called user-defined data type. Boolean Data Types Boolean data types represent any of the two values-true or false. JVM uses I bit to represent a boolean value internally, for example: 00 ean S onse r " As shown earlier, we should not enclose the boolean value true (or false) in any quotation mal'ks." in CjC++, 0 represents false and any other number represents true. This is not valid in Java. "terals A literal represents a value that is stored into a variable directly in the program. See the following examples: In the preceding statements, the right hand side values are called literals because these values are being stored into the variables shown at the left hand side. As the data type of the variable changes, the type of the literal also changes. So we have different types of literals. These are as follows: o Integer literals o Float literals o Character literals o String literals o Boolean literals Read on to get familiar with them.
- 51. ~ Chapter 4 Integer Literals Integer literaIs represent the fIxed integer values like 100, -55, 123450, etc. All these numbers belong to decimal system, which uses 10 digits (from 0 to 9) to represent any number. Suppose, we want to write an integer in octal number system (octal number system uses 8 digits, from 0 to 7), then· we should prefIx 0 before the number.· To represent hexadecimal number (hexadecimal number system uses 16 digits from 0 to 9 and from A to F), we should prefIx Ox before the value. Float Literals Float literals represent fractional numbers. These are the numbers with decimal points like 2.0, - 0.005, 3.14, 6.1e-22, etc. which should be used with float or double type variables. While writing these literals, we can use E or e for scientifIc notation, F or f for float literal, and D or d for double literal (this is the default and generally omitted). If. same value as dl, but in scientific notation -~ Character Literals Character literals indicate the following: . 0 General characters, like A, b, 9, etc. o Special characters, like ?, @, etc. o Unicode characters, like u0042 (this represents a in ISO Latin 1 character set). o Escape sequence (backslash codes) like n, b, etc. Character literals should be enclosed in single quotation marks. The preceding unicode characten and escape sequence can also be represented as strings. String Literals String literals repres'ent objects of String class. For example, Hello, Anil Kumar, AP1201, etc. wil come under string literals, which can be directly stored into a String object. Boolean Literals Boolean literals represent only two values-true and false, It means we can store either true or falSI into a boolean type vanable. Conclusion By following naming conventions, a programmer can avoid a lot of mistakes in writing the names 0 packages, classes, methods, variables, etc. This will improve readability as well as understandabili~ of a program. So maintaining naming conventions is a good programming habit. A program generally acts on data, processes it, and provides the results. So data is very importaI1 element of a program. In this chapter, we also discussed different data types, in terms of type ( data received, stored, or used in a program.
- 52. ~rs Ne 7), lal ile or rs CHAPTER OPERATORS IN. JAVA A programmer generally wants to do some operations in a program. For example, in a program, you want to perform addition of two numbers. How can you do it? Just by using + symbol, we can add the numbers. This means + is a symbol that performs an operation, i.e. addition. Such symbols are called operators and programming becomes easy because of them. Let us discuss about operators in this chapter and how to use them with examples. Operators An operator is a symbol that performs an operation. An operator acts on some variables, caped operands toget the desired result, as shown in Figure 5.1. rOperator ill I a + b ;e )f y It )f Operand Operand Figure 5.' Operator and operands If an operator acts on a single variable, it is called unary operator; if it acts on two variables, it is called binary operator; and if it acts on three variables, then it is called ternary operator. This is one type of classification. ·Let us now examine various types of operators in detail. Arithmetic Operators These operators are used to perform fundamental arithmetic operations like addition, subtraction, etc. There are 5 arithmetic operators in Java. Since these operators act on two operands at a time, these are called binary operators. Table 5.1 displays the functioning of these operators. Here, we are assuming the value of a as 13 and b as 5.
- 53. 18 8 Result a-b Subtraction operator Meaning Example .addition, operator a + h * Operator + Table 5.1 In this code snippet, the unary minus (-) operator is used on variable x to negate its value. The value of x is 5 in the beginning. It became -5 when unary minus is applied on it. Addition operator (+) is also 1,lsed to join two strings, as shown in the following code snippet: o String 51= "wel"; o String 52= "come"; o String 53= 51+52; Ilhere, '+' ~5 joining 51 and 52. Now, we get welcome in s3. In this case, + is called String concatenation operator. Increment Operator (++) This operator increases the value of a variable by 1, for example: Unary Operators As the name indicates, unary operators act on only one operand. There are 3 kinds of unary operators: o -Unary minus operator ( - ) o Increment operator ( ++ ) o Decrement operator ( -- ) Unary Minus Operator (-) This operator is used to negate a given value. Negation means converting a negative value into positive and vice versa, for example: 2!..JChapter 5
- 54. Operators in Java ~ Here, the value of the variable x is incremented by 1 when ++ operator is used before or after it.. Both are valid expressions in Java. Let us take an dmmple to understand it better: x= :i{+ • In this statement, if x is 3, then x+l value will be 4. This value is stored again in the left hand side variable x. So, the value of x now becomes 4. The same thing is done by ++ operator also. Writing ++ before a variable is called pre incrementation and writing ++ after a variable is called post incrementation. In p~e incrementation; incrementation" is done first and any other operation is done next. In post incrementation, all the other operations are done first and incrementation is done only at the end. To understand the difference between pre and post incremenations, let us take a couple of examples. Example 1: Finding the difference between pre- and post- increment ofx Output: Output: In this example, see the left-hand side and right-hand side statements. The second statement on the left uses pre-incrementation, while the second statement on the right uses post-incrementai:ion. At the left hand side: o System. out. println (x); I I displays the value of x as 1 o System. out .println (++x); I I first increments the value of x and then displays it as 2 o System.out.println (x); I I displays the value of x, which is already incremented, Le. 2 At the right hand side: o System.out.println(x); II displays the value of x, i.e. 1 o Sys"tem. out. println (x++) ; / / first displays the value of x as 1 and then increments it. o System. out.println (x); I I displays the incremented value of x, i. e. 2 Example 2: Finding the difference between pre- and post- increment of a and b
- 55. Exploring the Variety of Random Documents with Different Content
- 56. “I think that will suffice.” “And this?” asked the General. They read each other’s letters, expressed satisfaction, and then Waldron heard a slight click, the opening and shutting of a wallet. Some notes were counted out—to the sum of one thousand pounds. They rustled, and the listener knew that they were English notes so that they could not be traced so easily as those which the unscrupulous German contractor might withdraw from his own bank in Berlin. His Excellency counted them, declared the sum to be correct, and then, after a further brief conversation the German left, His Excellency remaining so as not to be seen in his company. The deal was concluded. Though interesting to Hubert, it however carried him no farther in his inquiry. It proved of course that General Cataldi, Minister of War, was corrupt and unscrupulous, yet were not the majority of the men who formed the Cabinet equally ready to accept bribes? He stood in that artistically furnished bedroom full of chagrin. He had practically had his journey there for nothing, and had lost valuable time by his absence from Rome. Therefore he slipped out along the corridor, and two hours later was on his way to Culoz, to catch the train-de-luxe from Paris to Rome. During that night as the express roared through the mountains he lay in his narrow sleeping-berth watching the green-shaded lamp above, and full of conflicting thoughts.
- 57. The attempt upon his life showed plainly that the thief was aware of the strenuous efforts he was making to fathom the mystery. But who was the thief! Was it this unscrupulous, much-decorated General who took secret commission of contractors, the man who allowed the army to be fed on discarded tin food, and go shod in cheap German boots which wore in holes on the first march, in order to enrich himself? Long and deeply he thought, and still the conviction clung to him that the person mainly responsible for the sale of the plans to Austria was His Excellency himself. Thoughts of Her Highness rose within him. He sighed. Yes, he loved her with all his body and soul. Yet that barrier of birth could never be bridged. After all, they could be only good friends, therefore he had never dared to declare his love. She was a Princess of the blood-royal and might marry a reigning Sovereign, but he was a mere diplomat, a secretary of Embassy, a man whom the Court regarded as the necessary adjunct of a practically defunct institution, for, however much one may cling in these days to the old usages and customs, yet the glaring fact must be faced that kings themselves are the ambassadors, and royal visits from one Court to another tend to cement more international friendships than ten years of that narrow little squabbling and intriguing world which exists in every capital under the name of the corps diplomatique. The public have been long enough gulled by the false tinsel and glamour of the diplomatic world, and in these ultra- modern days they see the inutility of it all. Often an obscure Vice-Consul in an obscure port is of greater use to the nation than the whole of the red-taped, ceremonious Embassy, with its splendid house, its dinners and dances, its
- 58. flunkeys and furbelows, and its flabby, do-nothing policy directed from Downing Street. Hubert Waldron, born and bred in the diplomatic atmosphere and nurtured upon the squabbles and petty jealousies of international politics, could not close his eyes to the fact that the public of Europe were being gulled daily by the Press, and that at an hour when all would seem quietest and most peaceful, the great and terrible European war would suddenly break out. Though at the Embassies you will be told that the peace of Europe is quite assured nowadays, and though your penny papers with their “advertised actual sales” will print reassuring leaders for the sake of the particular party who supports them, yet there is not a diplomat in all Europe who does not, in his own heart, fear a violent and bloody explosion and that brought about by the Dual Monarchy. Though this view may appear pessimistic, it is nevertheless a hard fact that the Powers of the Triple Alliance have not signed any agreements relating to the Mediterranean, and more than one European throne is to-day tottering to its fall, nay, more than one nation may, at any moment, be erased from the map. But the whole object of diplomacy is to reassure, not to alarm. The days when the greatest international tension exists are those when the outlook seems the most serene and unruffled. In our present century war breaks out; it is not declared. And war in Europe may break out at any moment, even though much is said of the solidity of the Triple Alliance. On arrival at the great echoing station at Rome, Hubert descended, tired and fagged, and took a taxi home.
- 59. It was then nine o’clock in the morning, and Peters, surprised to see him, handed him a letter which had been left on the previous night. On opening it he found it was from Ghelardi, dated from the Bureau of Secret Police, and asking when he could see him. At this request he was somewhat surprised in view of what had already passed between them, nevertheless he spoke to the functionary on the telephone at his private house and at eleven o’clock entered his private room at the Ministry. Their greeting was the reverse of cordial. Indeed Hubert had at first hesitated to meet him at all, yet he thought that the object of the interview might concern the unfortunate incident in the Palace; hence he went, determined to still show a bold front. “I regret, Signor Waldron, to have disturbed you,” the crafty old man said when his visitor was seated. “But it has been reported to me that the other night you were attacked by two individuals, and that you narrowly escaped with your life—that you shot and wounded both your assailants.” The policeman had, notwithstanding the bribe, evidently made a report in order to show his watchfulness to his superior. Hubert frowned in annoyance. “Oh, it was nothing at all,” he declared, laughing. “I had quite forgotten all about it. They were merely footpads, I suppose. No further notice need be taken of them.” “Ah! but they are very dangerous characters, and well- known in Rome,” he said. Then, looking straight at him the old man with the bristly hair said in a curious, half- suspicious voice: “You appear, Signor Waldron, to have some rather bitter enemies in Rome—eh?”
- 60. “I was not aware of it,” answered the diplomat. “If I have it does not trouble me in the least. I am perfectly able to defend myself.” “They are secret enemies, it seems,” Ghelardi said slowly, looking at his visitor meaningly. Hubert did not reply for a few moments. At last he said: “And they include yourself, Signor Commendatore.” The cunning old fellow smiled. “Ah, you are referring, I suppose, to that incident of the other night. Well, I think we may surely let that pass. We all of us have our hours of irresponsibility,” and he slowly twisted the diamond ring around his little finger, laughing lightly. “Thank you. I have no desire for your covert sneers, Signor Commendatore,” he said angrily, rising. “As I have told you —you are my secret enemy, and I shall treat you as such.” “It is rather a pity that you do so.” “A pity—why?” “For the sake of Her Royal Highness.” “Her name need not enter into our discussion,” Hubert said hotly, his hand upon the door ready to leave. “I do not see your object in troubling me to come here, merely to tell me of the attack made upon me by two criminals which the police should already have under lock and key. It is not much to the credit of the department that the streets of Rome are unsafe at night.”
- 61. “Ah! my dear signore, you are a little too impatient, I fear,” replied the chief of spies, quite undisturbed. “I was about to prove to you my friendliness.” “I desire none of your friendship,” declared the Englishman hotly. “And I tell you that I will not have you mention the name of the Princess Luisa in connection with my own.” “Friendships formed by Her Royal Highness are frequently unfortunate.” “Are they!” exclaimed Waldron, his eyes aflame. “If you were younger, Signor Commendatore, I would knock you down for your gratuitous insult. As it is, I shall not forget it. Buon giorno!” And he left the room, slamming the door after him.
- 62. Chapter Twenty Six. Gathering Clouds. Dust had once more been thrown into the eyes of Europe. Weeks had gone by, spring came, and the Roman season was on the wane. The month of May—the Primavera—with all its blossoms and ceremonies had opened. As far as the world knew not a cloud obscured the political horizon. In the chancelleries of Europe there were no sinister whispers, in the Embassies they danced and dined, the Archduke Francis Ferdinand had made a placid speech from the Throne, and Count Berchtold had declared the foreign policy of Austria-Hungary unchanged, and further, that the changes in the Near East had created new interests common to the Dual Monarchy and to Italy, and that their policy was leading them together along the path of co- operation, and also that their attitude towards each other tended to preserve the peace of Europe and to assure freedom and equilibrium in the Adriatic. It is always so. The calm is followed by the storm. At Vienna they were secretly completing their plans for a sudden coup against their neighbours, yet the true facts were known only in our own Intelligence Department in Whitehall, and the information had in turn been sent in a cipher dispatch to the Embassy in Rome. It was this dispatch which the Ambassador, receiving it one evening from the hand of the King’s messenger, who had brought it in hot haste direct from Downing Street, passed over to Hubert to decipher.
- 63. The information was highly alarming, to say the least. The British secret agent—a responsible Austrian official in the Ministry of War—reported that the great army massed in the Tyrol for manoeuvres was being kept there. A secret order had been issued to the Eighth, Tenth, and Thirteenth Army Corps to concentrate from the Adriatic across to the Danube, and at the same time the Ministry of Marine had issued orders to the navy recalling the Adriatic fleet which had been manoeuvring between Cattaro and Ragusa up to Trieste. The wireless stations at Sebenico and Pola had been taken over by the navy, and operators placed there sent expressly from the Ministry of Marine in Vienna. All tended to a secret attack—to war—a war in Europe with dreadnoughts, high explosives, aeroplanes, seaplanes, submarines, and wireless conditions never before imagined either in the wildest dreams of novelists or the ever-active brains of place-seeking party politicians. Preparations were slowly but surely being made in Vienna, and the blow would surely soon be struck. For an hour Waldron remained in consultation with his Chief. Then, regardless of Downing Street regulations, and only hoping to prevent the conflagration, he went back to his rooms on the ground floor of the Embassy, scribbled a hasty copy of the secret information, and with it walked direct to the Quirinale. Events would, he saw, very soon be moving fast. About six o’clock he entered the private room of the Minister of the Royal Household, that cosy, well- remembered apartment in which Ghelardi had discovered
- 64. him on his knees beside Her Royal Highness. The Minister himself was not in, but his secretary went immediately along to the private apartments and asked His Majesty for audience on Waldron’s behalf. The request was immediately granted, and he was at once shown up the long corridor, past the sentries guarding the door leading to the royal apartments, and on into the King’s private cabinet, where His Majesty, plainly dressed in dark blue serge—for he discarded uniform whenever he could— stood eagerly awaiting him. “Well, Waldron?” he exclaimed, stretching out his hand warmly, “I’ve been expecting you for days. Anything to report—eh?” For answer his visitor drew out the rough memorandum from his pocket, and after brief explanation regarding its source, proceeded to read it. His Majesty’s handsome, clear-cut face fell. He grew pale, but remained silent till the end. Then with his hands behind his back, he strode slowly across the soft carpet to the heavily curtained window and back again. Twice he paced the room in silence. “Strange, Waldron!” he said, pausing and standing before the diplomat. “Very strange that you get this information, yet Ghelardi is in ignorance of what is happening?” “He may not deem it wise to report to Your Majesty,” Hubert suggested.
- 65. “Wise!” he echoed. “In the interests of the country’s safety it is his first duty! He reports to me sufficient regarding trivial matters—the irresponsible vagaries of my niece, Lola, and things of that sort. Yet he knows nothing of what is in progress across the frontier,” the King cried in anger. “Again, he has discovered nothing regarding the theft of those plans. If we could but find out the truth we might easily face our friends in Vienna, and prevent this attack. Diplomacy could avert the explosion even now, if we only knew the identity of the spy.” “I have made every inquiry, Your Majesty, but I have, alas! failed.” “I can only suppose that the conspiracy must have been formed in our own camp,” was the King’s hard remark, and his visitor knew what was passing in His Majesty’s mind. Though Sovereign, he was not blind to the corruptness of his Ministry. Yet, as monarch, his hands were, alas! tied, or he would have long ago cleaned out the Augean stable. For an hour he remained with the King, discussing the seriousness of the international situation. “Ah, Waldron,” sighed His Majesty, as he stood before the fire, erect, almost statuesque, his face pale and hard-set, “my people little know how much responsibility rests upon me, or how heavy is the burden of my duties towards my nation. During these past weeks I have slept but little, and many a night have I passed in here alone, trying to devise some scheme whereby to defeat this secret plot against us. I have learnt how untiring have been your efforts to unravel the mystery of the theft, and I also know that a dastardly attempt has been made upon your life. I know how well and faithfully you have served me, even though I am not your
- 66. own King. I can only thank you most deeply. Your father was my father’s friend, and you are my friend.” “And I trust, even though I have failed to accomplish successfully the mission entrusted to me, that Your Majesty will still allow me to be your most faithful and devoted servant,” he replied. “I know you have done your very best, Waldron, and I highly appreciate it,” was the Sovereign’s earnest reply. “Ah!” he sighed, “if we could only discover the truth concerning those plans. Then, by prompt action, we might save the situation. But alas! it is still a mystery.” “Has Your Majesty formed any theory?” Hubert asked, after a few moments’ hesitation. “Only one—that Cataldi may have sought profit to himself.” Hubert Waldron nodded, but no word escaped him. “But how can we prove it—how can we prove it?” the King said. The Englishman shrugged his shoulders. He recollected that sum which had come to the Minister from a mysterious source a few days after the theft. But of that he made no mention to the King. It was, after all, no proof. Only a suspicion. Therefore, after yet another half an hour, he made his adieu, bowed as he backed out of the room, and then walked home full of gravest reflections. That same evening he had promised to see off at the station by the Milan express two English ladies who had been guests of Lady Cathcart at the Embassy, and this he did,
- 67. driving in the car with them, for the Ambassador himself had to be present at an official dinner given by the Minister of Foreign Affairs. He had bidden the two ladies farewell and the train had moved out of the station upon its long, northward journey when, just as he was about to enter the Ambassador’s car, standing in the piazza, he caught sight of a familiar face— that of Henri Pujalet. “Hallo?” he cried. “Why—you in Rome?” “Yes. I arrived only this afternoon,” responded Her Highness’s lover, halting and putting out his hand. He was well-dressed, though there seemed to have been some slight attempt to disguise his features. “Mademoiselle does not know I am here,” he added, “so if you see her, please do not mention this meeting. I shall not see her until the day after to-morrow—when we have an appointment to meet.” “Very well,” laughed Waldron, though, truth to tell, he was consumed by jealousy. Then in reply to a question he told Waldron that he was staying at the Hôtel de Russie, out by the Porta del Popolo, to which place Hubert gave him a lift, afterwards bidding him good evening and driving back to the Embassy. What further indiscretion, he wondered, was Lola about to commit. His heart was bursting with unspoken love. Night after night he lay and thought of her in wonder. Though she was in ignorance of it, she was his all-in-all. Since he had been in Rome he had danced attendance upon many women, as it was his duty as diplomat to do; he had laughed and flirted, and danced and gossiped, and kissed many a woman’s
- 68. hand, but in his heart he held them all in supreme indifference. His eyes and heart were only gladdened when Her Royal Highness, the scandalously skittish and unconventional, chanced to be present. This was fortunately often the case, and frequently he found himself in cosy corners or in conservatories with her as she whispered merrily behind her fan. This Frenchman, Pujalet, still knew her by the name she had used in her incognita in Egypt—Lola Duprez. Where, he wondered, would they hold their secret meeting? He bit his lip in mad jealousy as there arose before his eyes a vision of that far-off oasis of dark palms, the steely sky with the bright stars shining, and of two figures clasped breast to breast. Peters, as he entered his room, placed the evening paper before him. Taking it up mechanically he saw a heading: “Boots for the Army,” and read as follows: “It has just transpired, telegraphs our Berlin correspondent, that the tender for the supply of all boots to the Italian Army for the next three years has been secured by the well- known firm of Steinberg and Klein, of Friedenau, near Berlin. It will be remembered that last year they also secured the contract for supplying tinned meats and leather accoutrements for the expedition to Tripoli. The contract was signed by His Excellency General Cataldi some weeks ago, but has not been made public until to-day. The prices quoted by the English and French firms were lower, but His Excellency, after various tests, decided that the quality of the goods offered by the German firm was distinctly better.”
- 69. Waldron, with bitter words upon his lips, cast the journal from him viciously. A letter he opened was from Beatriz, dated from Moscow. She was having a brilliant success at the Opera there, she said. When could they meet? He tore it into small fragments and cast it into the wastepaper-basket. All thought of the handsome dancer who had used him merely as a stepping-stone to fame had now passed from him. He only remembered her with a feeling of poignant bitterness. Upon the mantelshelf a large, imposing card of invitation caught his eye. Peters sorted them out, and day by day placed them in that conspicuous spot so that he might be reminded of his engagements. The presence of the Honourable Hubert Waldron, M.V.O., was requested that night by His Excellency General Cataldi at an official reception at the Ministry of War. He smiled. Cataldi, the unscrupulous, corrupt member of the Cabinet, who was feathering his nest so comfortably, had, perhaps, hired those two assassins to take his life. And he was invited to his reception. The situation was not without its grim humour. Yes, he would go. He would watch further this man who was providing the brave, patriotic sons of Italy with uneatable beef and unwearable boots, in order that the Countess Cioni should be provided with funds. He rung up Pucci on the telephone, telling him where he was going. “You have entrée to the Ministry, Pucci, have you not?”
- 70. He heard the detective reply in the affirmative. “I may want you. So go there.” “I cannot go as guest, signore,” came the reply. “I will arrange, if you wish, to be on duty as a servant.” “Good. And be as near His Excellency’s private room as possible. I will meet you there at midnight and give you instructions. The reception is at eleven—after the banquet at the Ministry of Foreign Affairs. His Majesty will, no doubt, be there, and other members of the Royal Family.” “Benissimo, signore, I shall be in the corridor at midnight, acting as waiter.” Then Hubert rang off, and passing into his bedroom, got into uniform with the aid of the queer, under-sized, hunch- backed little man who, for so many years, had been his faithful servant, and whose father before him had been valet to Hubert’s father. At eleven o’clock Waldron stood before the long cheval glass arranging his tight uniform collar. Then he placed his decorations exactly at the right angle, settled the hang of his pearl-handled diplomatic sword, and took his white gloves from Peters’ hand. His face was dark and clouded. On the one hand he had no desire to meet the corrupt Minister who was bringing disaster and defeat upon his country, while on the other he knew that his Chief expected him to turn up there and be on show, as is the duty of those attached to the Embassies. His Majesty, too, would be there. What, in face of those words of his concerning His Excellency, could he think? Truly, the head upon which lies a crown must, indeed, be
- 71. very weary. How little does the general public know of that narrow, glittering, fevered world which, in every capital, surrounds a throne—that world where place-seekers intrigue, where money brings power, where morality is so often scoffed at as antiquated and out-of-date, and where the true, honest love of man and woman is forbidden because of rank and blood. How little do the readers of our daily Press ever dream of the many bitter romances of love that are to-day being enacted beneath the shadows of the thrones of Europe, for the social columns tell nothing save what those mentioned desire that the world shall know, while the scandals which find their way into print are only the sordid ones. How little, indeed, do the public dream of the hearts which lie broken near the thrones of Europe, of the mad passion, of the steel fetters of royalty, or of the true, honest affection of those beyond the pale. It is only when there is a morganatic marriage, or when a Prince or Princess of the blood-royal renounces their royal rights that that public pause for a second to reflect. And then, alas! they too often put it down to mental derangement. But the public are in ignorance of the world behind the walls of the royal palace, the pomp, the splendour, the officialdom, and, alas! the constant intrigue. Only those in the immediate entourage of the Sovereign and the diplomat know the truth. And, after all, it is that little fevered world of its own which rules the greater world outside. And so the Powers of Europe struggle on, one against the other, for wealth and supremacy. At eleven o’clock Hubert Waldron’s taxi drove into the great courtyard of the Ministry of War, that huge, handsome
- 72. building at the other end of the Via Venti Settembre to where the British Embassy was situated. As he descended, the sentries, noticing his uniform, saluted, and returning their salute, he entered the great vestibule, threw his cloak to one of the gorgeously dressed flunkeys, and with his cocked hat tucked beneath his arm made his way up the great red-carpeted staircase to the first floor where the reception was being held. As he went up he could hear the tuneful strains of dance music being played above by one of the military bands, bright military uniforms were everywhere, the place, usually so dark and sombre, had been adorned by flowers and palms, and was now brilliantly lit by festoons of coloured electric lamps. Italy, par excellence the country of the British tourist, has its charm even in its officialdom. At the top of the staircase stood the Minister himself, His Excellency General Cataldi, resplendent in his brilliant, gold- laced uniform, glittering with decorations, saluting as he received his guests. Hubert smiled bitterly within himself. He recollected that last occasion when, after travelling many miles, he had seen him driving to the Univers at Tours, and remembered the subsequent conversation when he had accepted the bribe to place brown-paper boots upon the feet of the Italian Army. He saw that His Excellency wished to behave with great cordiality as he passed. But he merely drew himself up, saluted, and passed on along the corridor. A second later he found himself face to face with the detective, Pucci, who, in plain evening-clothes as a waiter,
- 73. came up and bowed, and then, with darkly knit brows, motioned that he desired most anxiously to speak with him.
- 74. Chapter Twenty Seven. Reveals an Intrigue. Hubert Waldron, a smart figure in his diplomatic uniform, strolled along the corridor, followed at a respectable distance by the neatly-dressed waiter until, at a convenient point, the diplomat halted at the junction of two corridors, as though in doubt. Pucci was at his side in an instant. “I learnt only half an hour ago, signore, that there is a plot against you!” he said. “Signor Ghelardi is your enemy. You were attacked by the two assassins whom he bribed, but the conspiracy failed. Be careful. Exercise the greatest caution, signore—I beg of you.” “This is not news to me, Pucci,” replied the diplomat, pretending to button his white glove. “I am keeping observation upon His Excellency the Minister, so be near me to-night, and keep a sharp look-out. It is in the personal interests of His Majesty. Is he here?” “Si, signore. He arrived a quarter of an hour ago. I saluted him and he recognised me—even in this garb. His Majesty never forgets the faces of those whose duty it is to be his personal guardians.” “All right, Pucci. Be near in case I require you—I trust you.” “Bene, signore. I shall be there if you want me, never fear,” was the reply; of the faithful police agent. And then the British diplomat strolled up the corridor, leaving the waiter to bustle along in the opposite direction.
- 75. Pucci was full of resource. He had been attracted to Hubert Waldron because he had seen that he was a fine, strong character, a man of high ideals, of dogged courage, and of British bull-dog perseverance. Waldron, of the stock that had made the Empire what it is, commanded respect. He was a man of action and of honour. Though clever, far- seeing, and with a keen scent for mystery, yet he was honest, upright, and once he made a friend that friend was his for always. His only fault was that he was too generous towards his friends, or to those who were in want. He would give his last half-sovereign to anyone who told him a tale of poverty. In this connection he had often been imposed upon. He knew it, but always declared that, after all, he might have done one really charitable action, though others who had told their stories were impostors. Like most men possessed of keen wits, he had been very badly imposed upon at times. Yet often and often, by his sympathetic feelings, he had spent the greater part of his pay in the relief of real cases of distress. The Waldrons had ever been charitable, for they were always English gentlemen in the truest sense of the word. In the great Council Chamber with the huge crystal chandeliers, where the walls were hung with the ancient tapestries brought from the Palazzo Communale at Siena— the chamber in which the sittings of the Council of Defence were held, and where the lost plans had been discussed— the King stood, the brilliant, imposing centre of His Excellency’s guests. The assembly was a somewhat mixed one, though mainly military, and uniforms of every description were there, while
- 76. every second man wore decorations of one kind or another. The ladies were mostly wives of high officers of State, of prefects and of military men. Yet there was also the usual sprinkling of wives and daughters of deputies and senators. Monte Citorio is always much in evidence in every public function in Italy. Twice each year was the great imposing Ministry of War—or at least the public portion of it—thronged with officials from every corner of the kingdom, for His Excellency, General Cataldi, sent invitations broadcast, as he found it a cheap way of returning the hospitality daily offered to him— especially as the entertainment was paid for out of the public purse. Waldron, on entering the Council Chamber, made his bow before His Majesty, and then, after nodding acquaintance with many persons he knew, crossed to where the Princess Luisa was standing in conversation with a stout old General, the commandant on the Alpine frontier. He bowed over her hand, and then all three began to chatter, while a few moments later the secretary, Lambarini, approached and found the little group. Presently Lola, who was wearing a beautiful gown of pale carnation pink, and who looked inexpressibly sweet as she smiled, bent and whispered to Hubert: “We had better not be seen together to-night, I think. Let us meet to-morrow at noon, out at Frascati, as before. I must see you. It is most important.” “Good,” he replied. “That is an appointment,” and bending over her hand he passed across the great apartment, and was soon laughing merrily with Suderman, secretary of the Swedish Embassy.
- 77. He was rather annoyed that Lola—whom he had come there expressly to meet—should have ordered him to remain apart from her. What, he wondered, did she fear? When in her presence, the world was, to him, full of bright gladness, but when they were apart, he only moped in silence and despair. Did she know the truth, he wondered. Had she, by her woman’s keen, natural intuition, discovered that he loved her—that he was hers, body and soul? Though he laughed lightly with the tall, fair-haired Swede at his side, his thoughtful eyes were still upon her, full of supreme admiration. And once she glanced furtively at him, as though in fear, it seemed, and then he saw her accompany the fat old General out into the ante-chamber adjoining. For half an hour, or more, he remained talking with men and women he knew—the same old weary chatter of which the diplomat serving his country abroad grows so unutterably tired. Who, of all that gay throng save His Majesty himself, dreamed of the sharp-edged sword of war suspended above them? Who knew of the black peril which threatened the fair land of Italy, or of the carefully prepared plot which her enemies in Vienna had prepared against her. As Waldron stood chatting with a stout woman in black—the wife of one of the great Hebrew financiers of Genoa, he saw His Excellency enter and take his stand near the King, smiling serenely and bowing graciously to those about him —he, the man who was feeding the army upon tinned meat that had been rejected by the German authorities, and who
- 78. signed contracts in return for bundles of bank-notes. Ah! what a world is ours! But alas! is there not corruption in every Ministry of every European Power. What contractor to-day can hope to do a legitimate business without placing apart a sum for palm- oil? Disguise it as you will, business morality is in these days of grab and get-rich-quick, at a very low ebb, for too often, alas! honesty spells bankruptcy. A pretty young Countess was talking with Hubert as he stood watching His Excellency. Was the General, he wondered, the man who had hired the two ruffians, Merlo and Fiola, to make that murderous attack upon him? Or was it Ghelardi, as the detective, Pucci, had that night declared. Was it possible that the Chief of Secret Police had now found out the strenuous efforts he was making towards the elucidation of the problem of the stolen plans, and in consequence his jealousy had been aroused. Of which theory to accept he was utterly undecided. He was listening to the pretty woman’s inane chatter, hardly aware of what she said. His mind was far too full of the grave peril of the international situation. Suddenly his eyes wandered around to find Lambarini. He was there a few moments before, but he seemed to have left and passed into one or other of the ante-rooms. A point had arisen in his mind regarding the plans earlier that evening, and upon it he wished to ask him a question. The Council Chamber was now hot and stifling, and the mingled odours of the chiffons of the women nauseated him. He would have preferred to be in the quiet comfort of
- 79. his own rooms, now that Lola had sent him away. Yet was not his duty to be seen at that official reception? Dawson, the British military attaché, conspicuous in his Guards’ uniform, came up to him, saying in a low voice: “Hallo, Hubert, you look a bit bored, my dear boy. So am I. Couldn’t we clear out, do you think? I’m going to play bridge down at the club. Come?” “Not to-night, old chap,” Hubert answered. “I shall stay another quarter of an hour, and then toddle home.” “Sure you won’t—eh?” “No, not to-night. I’m tired.” “Right-ho! Good night,” answered the attaché cheerily, and was next moment lost in the crowd. Waldron pushed his way through the throng into the ante-chamber, vainly searching for Lambarini. Pironti, the unscrupulous secretary of the Minister was there, surrounded by women—wives of officers and others who hoped to secure the man’s good graces to procure better appointments for their husbands. In the army it was openly declared that Pironti was necessary in order to secure His Excellency’s ear, and many a man had been passed over his superior’s heads and given lucrative jobs because Pironti’s palm had been crossed by a few bank-notes. Presently, tired to death of the incessant laughter and chatter, Hubert left by a door which he knew led to a long corridor, which ended with a flight of stairs to the first floor. On the nights of Ministerial receptions the sentries had orders to allow guests to pass without hindrance and
- 80. unchallenged throughout the building, therefore, as Hubert ascended the stairs the soldier stood at attention. Above, was another wide corridor leading right round the first floor to where was situated General Cataldi’s private cabinet in the centre of the huge, handsome pile overlooking the broad Via Venti Settembre. To that part of the building few of the guests penetrated, save perhaps some officials who took their wives to see the fine suite of rooms occupied by His Excellency the Minister. Hubert was still in search of Lambarini, and was wondering if he had gone in that direction. At some distance down the corridor from the door of His Excellency’s private cabinet two sentries, their duties relaxed that night, stood at ease chatting, but as Hubert passed they drew themselves to attention, while around a corner from another corridor which ran at right angles a waiter with a silver salver in his hand hurried by. The man’s face struck Waldron as peculiarly familiar, yet he saw it only for a second, as the man seemed in a great hurry. It was not Pucci, for he had not seen him since he had first entered the building. Hubert halted and looked after the receding figure, much puzzled. His clothes did not fit him, for the tails of his dress- coat were too long, and the trousers also were too big. Apparently, he seemed of middle-age, with a short moustache turning slightly grey, yet in his eyes, in that brief second when their glance had met, there was an expression that was familiar.
- 81. “Who can he be?” murmured Hubert to himself. “I know him. But for the life of me I can’t recollect where we’ve met before.” The man who travels comes frequently across familiar waiters in all sorts of out-of-the-way places. Therefore, after reflection, he came to the conclusion that it must be a man who had served him somewhere or other in the past. And he went forward to His Excellency’s rooms—that room wherein, on the last occasion, he had discussed the stolen plans with Cataldi and the two secretaries. No one was nigh. The sentry still stood gossiping at the other end of the corridor. He would enter and have yet another look at that big safe which had been so mysteriously opened, though no one appeared to have entered there. He turned the handle of the big door of polished mahogany. It yielded noiselessly, and pushing it open, he stood upon the thick, Oriental carpet in the too familiar room. He halted upon the threshold, scarce believing his own eyes. Before the Minister’s safe—the same one from which the plans had been stolen—stood a woman—Lola! The safe door stood open, and as he looked he watched her abstract an envelope, which she folded hurriedly with nervous hands and thrust into the breast of her gown, at the same time producing a similar envelope which she put in the place of the one she had stolen. So noiselessly had he entered that she was all unconscious of his presence.
- 82. His heart gave a great bound and he held his breath. His senses were frozen by the amazing and horrifying discovery. With staring eyes he watched her breathlessly, as with hurried hands she closed the heavy safe door, turned the small key twice and then slipped it into her long white glove, at the same time crushing the stolen envelope deeper down into the breast of her low-cut dress. For a second she remained motionless. Then she tried the safe door in order to reassure herself that it was securely locked, and turned to leave. But as she did so a low cry escaped her hard, white lips. She found herself face to face with Hubert Waldron.
- 83. Chapter Twenty Eight. The Eyewitness. “Princess!” “You!” she gasped, staring at him, her face white as death, and clutching at the back of a chair for support. “Yes. I see now why you were so anxious that I should not remain in your company this evening,” he said in bitter reproach. “Then—then you know!” she cried. “You—you saw me!” “Yes. I have been watching you, and I can only say that I am surprised to find you tampering with His Excellency’s safe!” he said in a low, hard tone, while, as ill-luck would have it, old Ghelardi, in uniform, with a glittering star upon his coat, entered the room just at that moment and overheard part of the diplomat’s words. “Ah!” said the crafty Chief of Secret Police, affecting not to have overheard anything. “Ah! these assignations—eh?” She raised her hand towards him in a quick gesture, but from her glove, there fell the small key. Ghelardi stooped and picked it up. “Hallo!” he exclaimed, “what does this mean, Your Highness? A safe key!” The unhappy girl, white as death, nodded in the affirmative.
- 84. The white-haired official stepped across, drew the brass cover aside from the keyhole, and tried the key. It yielded. “And may I ask Your Royal Highness why I find you here, in His Excellency’s room, with a key to his private safe wherein, I believe, many secrets of our defences are kept?” he asked of her. “I refuse to answer you, Signor Commendatore,” was her bold reply, as she drew herself up and faced him. “You have no right to question me. I shall answer only to His Majesty for what I have done.” This bold declaration took Hubert aback. “Very well,” replied the old man, pocketing the key and smiling that strange, cunning smile of his. “Your Highness shall be compelled to answer to him—and without very much delay.” And he turned on his heel and without a word left the room. “Ah! Mr Waldron,” she cried, wringing her hands, “what must you think of me? I know I have acted very foolishly— that I am mad—that I—” “Hush, Princess!” he said, his heart full of sympathy for her in her wild distress. “You have acted wrongly, it is true— very, very wrongly. Yet I am still your friend. I will see you safely out of this impasse—if you will only allow me. What is that document you have abstracted from the safe?” She made no response, but placing her hand within her breast she very slowly drew it out and handed it to him. Without opening the envelope he placed it in his pocket. Then taking her hand, he looked long and earnestly into her
- 85. face and said: “You had better return to the Palace at once, Lola. You are not well. Leave me to settle matters with Ghelardi.” “But he will tell the King!” she gasped, wringing her hands in despair. “What can I say—how shall I explain?” “Leave all to me,” he urged. “But before you go, tell me one thing. Why is Henri Pujalet in Rome?” “No, no!” she shrieked, “do not mention his name. I—ah! no —do not torture me, I beg of you!” she went on wildly. “Hate me—denounce me as a spy, if you will—revile my memory if you wish—but do not taunt me with the name of that man.” “I will see you to your carriage. Come,” he urged simply. She struggled to calm herself, placing her gloved hand upon her beating heart, while the Englishman laid his hand tenderly upon her shoulder in deepest sympathy. At first he had been horrified at discovering the bitter, amazing truth. But horror had now been succeeded by poignant regret and a determination to suppress, if possible, what must be, if divulged by Ghelardi, as no doubt it would—a most terrible national scandal. While they were standing together, a Colonel of Artillery and two ladies entered, the former showing them the private cabinet of the head of the War Department. The women recognised the Princess by the decoration she wore at the edge of her bodice, and bowed low and awkwardly before her as she passed out, followed by Hubert.
- 86. With hurried steps he conducted her to the main entrance, and at once sent a servant for one of the royal automobiles, saying that Her Royal Highness was not well. Together they waited in an ante-room almost without speaking. She seemed too nervous and overwrought. “I trust you, Mr Waldron,” she said suddenly, looking up into his face. “Yet—ah! what can you think of me! How you must scorn and despise me! But—but I hope you will not misjudge me—that—you will make allowances for me—a girl —a very foolish girl?” “Do not let us discuss that now,” he hastened to reply in a low, hard voice, for he never knew until that moment how mad was his affection for her. And just then one of the royal flunkeys entered, bowing, to announce that the car was awaiting Her Royal Highness. Their hands clasped in silence, and she walked out through a line of obsequious servants and down the flight of steps to the royal car. As she went out a waiter stood behind the line of soldiers drawn up in the great vestibule, watching intently. Unobserved he had followed the pair when they had emerged from His Excellency’s private cabinet, and his shrewd eyes had noticed something amiss. He was the same man who had passed Hubert earlier in the evening and whose face had so puzzled him. The Englishman, after the royal car had driven away, turned and made his way back in search of Ghelardi.
- 87. The discovery held him utterly confounded. What secret was contained in that envelope she had stolen? Why had she a key to the Minister’s safe? As he walked back, his mind tortured by a thousand strange thoughts and curious theories, the mysterious waiter followed him at a respectable distance, watching. Hubert was wondering what had become of Pucci whom he ordered to be near him, and whom he had not seen the whole evening. He gained the door of His Excellency’s room just as the Chief of Secret Police returned along the corridor. “I have been endeavouring to discover His Excellency, but, unfortunately, I cannot find him anywhere,” the old man said. “We will open the safe and see what has been taken. It is utterly astounding to me that the Princess Luisa should be revealed as a spy.” “I do not think we should condemn her yet,” urged Waldron. “There may be some explanation.” “Explanation! What explanation can there be of a woman who takes advantage of a reception, when the sentries are relaxed, to creep up here, open the safe with a false key, and abstract documents.” “I cannot see the motive,” declared Waldron. “Ah! but I do. I and my agents have been watching for weeks,” he replied, and crossing to the safe he placed the key in the lock and again opened it. Many formidable bundles of documents were disclosed, lying within, together with the thin envelope with which Lola
- 88. had replaced the one she had taken. Waldon took it up and turned it over with curiosity. Then, deliberately tearing it open, he pulled out its contents. It was, he found to his dismay, only a blank piece of tracing paper! “Ah! that is what she has placed here, after taking out a similar envelope, I suppose,” snapped the keen-eyed old man, grasping the situation in a moment. “I have suspected this all along—ever since those fortress plans so mysteriously disappeared. And now she has taken another document. I was foolish to allow her to leave with you.” “The document—or whatever it is—is in my safe keeping.” “You have it!” he cried quickly. “Please hand it to me.” “I shall do no such thing, Commendatore,” was Hubert’s defiant reply. “It is a secret of State, and you, as a foreigner, have no right to its possession!” “It has been given to me for safety, and I shall hand it over to His Majesty, and to him alone.” “Signor Waldron, I demand it,” the old man said angrily, raising his voice as he flung the safe door to with a clang and re-locked it. “I demand it—in the name of His Majesty!” “And I refuse.” “You defy me then?” “Yes, I defy you, signore,” he replied firmly, his dark eyes fixed upon those of the crafty official.
- 89. “You are Her Highness’s lover. When the King is made aware of that fact he will show you little graciousness, I assure you,” said Ghelardi with a dry laugh. “But you will remain silent upon that point, just as you will remain silent regarding what we have discovered to-night,” the Englishman said slowly. “No scandal must attach to the Princess’s name, remember.” “Of course you wish to shield her—for your own ends. She is the spy for whom we have been searching all these weeks. It is she who placed in the hands of the our enemies the truth concerning the new fortifications along the northern frontier.” “I refuse to discuss that point,” replied Hubert very coldly, but firmly. “One thing alone I demand of you, and that is silence—silence most absolute and profound.” “It is my duty to inform the King of the whole circumstances.” “True, it may be your duty, but it is one that you will not perform, Signor Ghelardi. Think of the terrible scandal throughout Europe if the Press got wind of it! And they must do—if you report officially, and it comes to the ears of His Excellency the Minister. The latter hates the Princess, because she accidentally snubbed the Countess Cioni at the ball at the Palazzo Ginori last week.” “That is no affair of mine. Women’s jealousies do not concern me in the least. I am charged with the safety of the State against foreign espionage.” “Well—in this case you’ve discovered the truth accidentally,” responded the diplomat, “and having done so, if you respect your Sovereign and his family, you will say nothing. Further,
- 90. we may, if we remain silent, be able to obtain more information from Her Highness as to the identity of the person into whose hands the plans fell.” “She abstracted them, without a doubt, for she had this duplicate key of the safe,” the old man declared. “You will say nothing, I command you.” “You! How can you impose silence upon me, pray?” he demanded fiercely. “You are a foreigner, and you are holding a State secret.” “I shall hold it at present for safe keeping.” “Then I shall go straight to the King and lay the whole matter before him.” “You threatened to do a similar action before,” said the other very quietly. “I repeat my warning—that silence is best.” “Then I tell you frankly that I refuse to heed your warning. It is my duty to my Sovereign to tell him the truth.” “Very well—go to him and tell him—at your own peril.” “Peril!” he echoed. “What peril?” “The peril at which I have already hinted, Signor Ghelardi,” he answered in a low, hard voice. “Do you wish me to be more explicit? Well—there is in a village called Wroxham, in Norfolk, a mystery—the murder of a man named Arthur Benyon, a British naval officer—which has never yet been cleared up. One man can clear it up—an eyewitness who is, fortunately, still alive and who knows you. And if it is cleared up, then you, Luigi Ghelardi—who at the time
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