![A Simple Java Program
Listing 1.1
//This program prints Welcome to Java!
public class Welcome {
public static void main(String[] args) {
System.out.println("Welcome to Java!");
}
}
IMPORTANT NOTE: (1) To enable the buttons, you must
Welcome download the entire slide file slide.zip and unzip the files
into a directory (e.g., c:slide) . (2) You must have installed
Run JDK and set JDK‟s bin directory in your environment path
(e.g., c:Program Filesjavajdk1.7.0bin in your
environment path. (3) If you are using Office 2010, check
PowerPoint2010.doc located in the same folder with this ppt
file.
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![Creating, Compiling, and
Running Programs
Create/Modify Source Code
Source code (developed by the programmer)
Saved on the disk
public class Welcome {
public static void main(String[] args) {
System.out.println("Welcome to Java!"); Source Code
}
}
Compile Source Code
Byte code (generated by the compiler for JVM i.e., javac Welcome.java
to read and interpret, not for you to understand)
…
Method Welcome() If compilation errors
0 aload_0 stored on the disk
…
Bytecode
Method void main(java.lang.String[])
0 getstatic #2 …
3 ldc #3 <String "Welcome to
Java!">
5 invokevirtual #4 …
8 return Run Byteode
i.e., java Welcome
Result
Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 If runtime Education, Inc. All
Pearson errors or incorrect result
rights reserved.
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![animation
Trace a Program Execution
Enter main method
//This program prints Welcome to Java!
public class Welcome {
public static void main(String[] args) {
System.out.println("Welcome to Java!");
}
}
Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All
rights reserved.
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![animation
Trace a Program Execution
Execute statement
//This program prints Welcome to Java!
public class Welcome {
public static void main(String[] args) {
System.out.println("Welcome to Java!");
}
}
Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All
rights reserved.
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![animation
Trace a Program Execution
//This program prints Welcome to Java!
public class Welcome {
public static void main(String[] args) {
System.out.println("Welcome to Java!");
}
}
print a message to the
console
Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All
rights reserved.
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![Class Name
Every Java program must have at least one class.
Each class has a name. By convention, class names
start with an uppercase letter. In this example, the
class name is Welcome.
//This program prints Welcome to Java!
public class Welcome {
public static void main(String[] args) {
System.out.println("Welcome to Java!");
}
}
Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All
rights reserved.
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![Main Method
Line 2 defines the main method. In order to run a
class, the class must contain a method named main.
The program is executed from the main method.
//This program prints Welcome to Java!
public class Welcome {
public static void main(String[] args) {
System.out.println("Welcome to Java!");
}
}
Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All
rights reserved.
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![Statement
A statement represents an action or a sequence of
actions. The statement System.out.println("Welcome to
Java!") in the program in Listing 1.1 is a statement to
display the greeting "Welcome to Java!“.
//This program prints Welcome to Java!
public class Welcome {
public static void main(String[] args) {
System.out.println("Welcome to Java!");
}
}
Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All
rights reserved.
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![Statement Terminator
Every statement in Java ends with a semicolon (;).
//This program prints Welcome to Java!
public class Welcome {
public static void main(String[] args) {
System.out.println("Welcome to Java!");
}
}
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rights reserved.
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![Reserved words
Reserved words or keywords are words that have a
specific meaning to the compiler and cannot be used for
other purposes in the program. For example, when the
compiler sees the word class, it understands that the word
after class is the name for the class.
//This program prints Welcome to Java!
public class Welcome {
public static void main(String[] args) {
System.out.println("Welcome to Java!");
}
}
Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All
rights reserved.
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![Blocks
A pair of braces in a program forms a block that groups
components of a program.
public class Test {
public static void main(String[] args) { Class block
System.out.println("Welcome to Java!"); Method block
}
}
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![Special Symbols
Character Name Description
{} Opening and closing Denotes a block to enclose statements.
braces
() Opening and closing Used with methods.
parentheses
[] Opening and closing Denotes an array.
brackets
// Double slashes Precedes a comment line.
" " Opening and closing Enclosing a string (i.e., sequence of characters).
quotation marks
; Semicolon Marks the end of a statement.
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![{ …}
// This program prints Welcome to Java!
public class Welcome {
public static void main(String[] args) {
System.out.println("Welcome to Java!");
}
}
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rights reserved.
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![( … )
// This program prints Welcome to Java!
public class Welcome {
public static void main(String[] args) {
System.out.println("Welcome to Java!");
}
}
Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All
rights reserved.
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![;
// This program prints Welcome to Java!
public class Welcome {
public static void main(String[] args) {
System.out.println("Welcome to Java!");
}
}
Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All
rights reserved.
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![// …
// This program prints Welcome to Java!
public class Welcome {
public static void main(String[] args) {
System.out.println("Welcome to Java!");
}
}
Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All
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!["…"
// This program prints Welcome to Java!
public class Welcome {
public static void main(String[] args) {
System.out.println("Welcome to Java!");
}
}
Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All
rights reserved.
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![Block Styles
Use end-of-line style for braces.
Next-line public class Test
style {
public static void main(String[] args)
{
System.out.println("Block Styles");
}
}
End-of-line
style
public class Test {
public static void main(String[] args) {
System.out.println("Block Styles");
}
}
Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All
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![Syntax Errors
public class ShowSyntaxErrors {
public static main(String[] args) {
System.out.println("Welcome to Java);
}
}
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rights reserved.
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![Runtime Errors
public class ShowRuntimeErrors {
public static void main(String[] args) {
System.out.println(1 / 0);
}
}
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rights reserved.
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![Logic Errors
public class ShowLogicErrors {
public static void main(String[] args) {
System.out.println("Celsius 35 is Fahrenheit degree ");
System.out.println((9 / 5) * 35 + 32);
}
}
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JavaYDL1
- 1. Chapter 1 Introduction to Computers, Programs, and Java Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 1
- 2. Objectives To understand computer basics, programs, and operating systems (§§1.2–1.4). To describe the relationship between Java and the World Wide Web (§1.5). To understand the meaning of Java language specification, API, JDK, and IDE (§1.6). To write a simple Java program (§1.7). To display output on the console (§1.7). To explain the basic syntax of a Java program (§1.7). To create, compile, and run Java programs (§1.8). To display output using the JOptionPane message dialog boxes (§1.9). To become familiar with Java programming style and documentation (§1.10). To explain the differences between syntax errors, runtime errors, and logic errors (§1.11). Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 2
- 3. What is a Computer? A computer consists of a CPU, memory, hard disk, floppy disk, monitor, printer, and communication devices. Bus Storage Communication Input Output Devices Memory CPU Devices Devices Devices e.g., Disk, CD, e.g., Modem, e.g., Keyboard, e.g., Monitor, and Tape and NIC Mouse Printer Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 3
- 4. CPU The central processing unit (CPU) is the brain of a computer. It retrieves instructions from memory and executes them. The CPU speed is measured in megahertz (MHz), with 1 megahertz equaling 1 million pulses per second. The speed of the CPU has been improved continuously. If you buy a PC now, you can get an Intel Pentium 4 Processor at 3 gigahertz (1 gigahertz is 1000 megahertz). Bus Storage Communication Input Output Memory CPU Devices Devices Devices Devices e.g., Disk, CD, e.g., Modem, e.g., Keyboard, e.g., Monitor, and Tape and NIC Mouse Printer Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 4
- 5. Memory Memory is to store data and program instructions for CPU to execute. A memory unit is an ordered sequence of bytes, each holds eight bits. A program and its data must be brought to memory before they can be executed. A memory byte is never empty, but its initial content may be meaningless to your program. The current content of a memory byte is lost whenever new information is placed in it. Bus Storage Communication Input Output Memory CPU Devices Devices Devices Devices e.g., Disk, CD, e.g., Modem, e.g., Keyboard, e.g., Monitor, and Tape and NIC Mouse Printer Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 5
- 6. How Data is Stored? Data of various kinds, such as numbers, characters, and strings, are encoded as a series of bits (zeros and ones). Computers use zeros and ones because digital devices Memory address Memory content have two stable states, which are referred to as zero and one by convention. The . . programmers need not to be concerned about . . . . the encoding and decoding of data, which is 2000 01001010 Encoding for character „J‟ performed automatically by the system based 2001 01100001 Encoding for character „a‟ on the encoding scheme. The encoding 2002 01110110 Encoding for character „v‟ scheme varies. For example, character „J‟ is 2003 01100001 Encoding for character „a‟ represented by 01001010 in one byte. A 2004 00000011 Encoding for number 3 small number such as three can be stored in a single byte. If computer needs to store a large number that cannot fit into a single byte, it uses a number of adjacent bytes. No two data can share or split a same byte. A byte is the minimum storage unit. Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 6
- 7. Storage Devices Memory is volatile, because information is lost when the power is off. Programs and data are permanently stored on storage devices and are moved to memory when the computer actually uses them. There are three main types of storage devices:Disk drives (hard disks and floppy disks), CD drives (CD-R and CD-RW), and Tape drives. Bus Storage Communication Input Output Memory CPU Devices Devices Devices Devices e.g., Disk, CD, e.g., Modem, e.g., Keyboard, e.g., Monitor, and Tape and NIC Mouse Printer Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 7
- 8. Output Devices: Monitor The monitor displays information (text and graphics). The resolution and dot pitch determine the quality of the display. Bus Storage Communication Input Output Memory CPU Devices Devices Devices Devices e.g., Disk, CD, e.g., Modem, e.g., Keyboard, e.g., Monitor, and Tape and NIC Mouse Printer Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 8
- 9. Monitor Resolution and Dot Pitch resolution The screen resolution specifies the number of pixels in horizontal and vertical dimensions of the display device. Pixels (short for “picture elements”) are tiny dots that form an image on the screen. A common resolution for a 17-inch screen, for example, is 1,024 pixels wide and 768 pixels high. The resolution can be set manually. The higher the resolution, the sharper and clearer the image is. dot pitch The dot pitch is the amount of space between pixels, measured in millimeters. The smaller the dot pitch, the sharper the display. Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 9
- 10. Communication Devices A regular modem uses a phone line and can transfer data in a speed up to 56,000 bps (bits per second). A DSL (digital subscriber line) also uses a phone line and can transfer data in a speed 20 times faster than a regular modem. A cable modem uses the TV cable line maintained by the cable company. A cable modem is as fast as a DSL. Network interface card (NIC) is a device to connect a computer to a local area network (LAN). The LAN is commonly used in business, universities, and government organizations. A typical type of NIC, called 10BaseT, can transfer data at 10 mbps (million bits per second). Bus Storage Communication Input Output Memory CPU Devices Devices Devices Devices e.g., Disk, CD, e.g., Modem, e.g., Keyboard, e.g., Monitor, and Tape and NIC Mouse Printer Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 10
- 11. Programs Computer programs, known as software, are instructions to the computer. You tell a computer what to do through programs. Without programs, a computer is an empty machine. Computers do not understand human languages, so you need to use computer languages to communicate with them. Programs are written using programming languages. Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 11
- 12. Programming Languages Machine Language Assembly Language High-Level Language Machine language is a set of primitive instructions built into every computer. The instructions are in the form of binary code, so you have to enter binary codes for various instructions. Program with native machine language is a tedious process. Moreover the programs are highly difficult to read and modify. For example, to add two numbers, you might write an instruction in binary like this: 1101101010011010 Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 12
- 13. Programming Languages Machine Language Assembly Language High-Level Language Assembly languages were developed to make programming easy. Since the computer cannot understand assembly language, however, a program called assembler is used to convert assembly language programs into machine code. For example, to add two numbers, you might write an instruction in assembly code like this: ADDF3 R1, R2, R3 Assembly Source File Machine Code File … Assembler … ADDF3 R1, R2, R3 1101101010011010 … … Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 13
- 14. Programming Languages Machine Language Assembly Language High-Level Language The high-level languages are English-like and easy to learn and program. For example, the following is a high-level language statement that computes the area of a circle with radius 5: area = 5 * 5 * 3.1415; Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 14
- 15. Popular High-Level Languages Language Description Ada Named for Ada Lovelace, who worked on mechanical general-purpose computers. The Ada language was developed for the Department of Defense and is used mainly in defense projects. BASIC Beginner‟s All-purpose Symbolic Instruction Code. It was designed to be learned and used easily by beginners. C Developed at Bell Laboratories. C combines the power of an assembly language with the ease of use and portability of a high-level language. C++ C++ is an object-oriented language, based on C. C# Pronounced “C Sharp.” It is a hybrid of Java and C++ and was developed by Microsoft. COBOL COmmon Business Oriented Language. Used for business applications. FORTRAN FORmula TRANslation. Popular for scientific and mathematical applications. Java Developed by Sun Microsystems, now part of Oracle. It is widely used for developing platform- independent Internet applications. Pascal Named for Blaise Pascal, who pioneered calculating machines in the seventeenth century. It is a simple, structured, general-purpose language primarily for teaching programming. Python A simple general-purpose scripting language good for writing short programs. Visual Visual Basic was developed by Microsoft and it enables the programmers to rapidly develop Basic graphical user interfaces. Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 15
- 16. Interpreting/Compiling Source Code A program written in a high-level language is called a source program or source code. Because a computer cannot understand a source program, a source program must be translated into machine code for execution. The translation can be done using another programming tool called an interpreter or a compiler. Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 16
- 17. Interpreting Source Code An interpreter reads one statement from the source code, translates it to the machine code or virtual machine code, and then executes it right away, as shown in the following figure. Note that a statement from the source code may be translated into several machine instructions. High-level Source File … Output area = 5 * 5 * 3.1415; Interpreter ... Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 17
- 18. Compiling Source Code A compiler translates the entire source code into a machine-code file, and the machine-code file is then executed, as shown in the following figure. High-level Source File Machine-code File … … Output area = 5 * 5 * 3.1415; Compiler 0101100011011100 Executor ... 1111100011000100 … ... Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 18
- 19. Operating Systems The operating system (OS) is a program that manages and controls User a computer‟s activities. The popular operating systems for Application Programs general-purpose computers are Microsoft Windows, Mac Operating System OS, and Linux. Application programs, such as a Web Hardware browser or a word processor, cannot run unless an operating system is installed and running on the computer. Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 19
- 20. Why Java? The answer is that Java enables users to develop and deploy applications on the Internet for servers, desktop computers, and small hand-held devices. The future of computing is being profoundly influenced by the Internet, and Java promises to remain a big part of that future. Java is the Internet programming language. Java is a general purpose programming language. Java is the Internet programming language. Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 20
- 21. Java, Web, and Beyond Java can be used to develop Web applications. Java Applets Java Web Applications Java can also be used to develop applications for hand-held devices such as Palm and cell phones Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 21
- 22. Examples of Java‟s Versatility (Applets) Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 22
- 23. PDA and Cell Phone Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 23
- 24. Java‟s History James Gosling and Sun Microsystems Oak Java, May 20, 1995, Sun World HotJava – The first Java-enabled Web browser Early History Website: http://www.java.com/en/javahistory/index.jsp Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 24
- 25. Companion Website Characteristics of Java Java Is Simple Java Is Object-Oriented Java Is Distributed Java Is Interpreted Java Is Robust Java Is Secure Java Is Architecture-Neutral Java Is Portable Java's Performance Java Is Multithreaded Java Is Dynamic www.cs.armstrong.edu/liang/JavaCharacteristics.pdf Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 25
- 26. Companion Website Characteristics of Java Java Is Simple Java is partially modeled on C++, but greatly simplified and improved. Some people refer to Java Is Object-Oriented Java as "C++--" because it is like C++ but Java Is Distributed with more functionality and fewer negative aspects. Java Is Interpreted Java Is Robust Java Is Secure Java Is Architecture-Neutral Java Is Portable Java's Performance Java Is Multithreaded Java Is Dynamic Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 26
- 27. Companion Website Characteristics of Java Java Is Simple Java is inherently object-oriented. Although many object-oriented languages Java Is Object-Oriented began strictly as procedural languages, Java Is Distributed Java was designed from the start to be object-oriented. Object-oriented Java Is Interpreted programming (OOP) is a popular Java Is Robust programming approach that is replacing Java Is Secure traditional procedural programming techniques. Java Is Architecture-Neutral Java Is Portable One of the central issues in software development is how to reuse code. Object- Java's Performance oriented programming provides great Java Is Multithreaded flexibility, modularity, clarity, and reusability through encapsulation, Java Is Dynamic inheritance, and polymorphism. Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 27
- 28. Companion Website Characteristics of Java Java Is Simple Distributed computing involves several computers working together on a network. Java Is Object-Oriented Java is designed to make distributed Java Is Distributed computing easy. Since networking capability is inherently integrated into Java Is Interpreted Java, writing network programs is like Java Is Robust sending and receiving data to and from a Java Is Secure file. Java Is Architecture-Neutral Java Is Portable Java's Performance Java Is Multithreaded Java Is Dynamic Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 28
- 29. Companion Website Characteristics of Java Java Is Simple You need an interpreter to run Java programs. The programs are compiled into Java Is Object-Oriented the Java Virtual Machine code called Java Is Distributed bytecode. The bytecode is machine- independent and can run on any machine Java Is Interpreted that has a Java interpreter, which is part of Java Is Robust the Java Virtual Machine (JVM). Java Is Secure Java Is Architecture-Neutral Java Is Portable Java's Performance Java Is Multithreaded Java Is Dynamic Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 29
- 30. Companion Website Characteristics of Java Java Is Simple Java compilers can detect many problems that would first show up at execution time Java Is Object-Oriented in other languages. Java Is Distributed Java has eliminated certain types of error- Java Is Interpreted prone programming constructs found in Java Is Robust other languages. Java Is Secure Java has a runtime exception-handling Java Is Architecture-Neutral feature to provide programming support Java Is Portable for robustness. Java's Performance Java Is Multithreaded Java Is Dynamic Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 30
- 31. Companion Website Characteristics of Java Java Is Simple Java Is Object-Oriented Java Is Distributed Java Is Interpreted Java implements several security Java Is Robust mechanisms to protect your system against Java Is Secure harm caused by stray programs. Java Is Architecture-Neutral Java Is Portable Java's Performance Java Is Multithreaded Java Is Dynamic Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 31
- 32. Companion Website Characteristics of Java Java Is Simple Java Is Object-Oriented Java Is Distributed Java Is Interpreted Java Is Robust Java Is Secure Java Is Architecture-Neutral Write once, run anywhere Java Is Portable With a Java Virtual Machine (JVM), Java's Performance you can write one program that will Java Is Multithreaded run on any platform. Java Is Dynamic Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 32
- 33. Companion Website Characteristics of Java Java Is Simple Java Is Object-Oriented Java Is Distributed Java Is Interpreted Java Is Robust Java Is Secure Java Is Architecture-Neutral Java Is Portable Because Java is architecture neutral, Java programs are portable. They can Java's Performance be run on any platform without being Java Is Multithreaded recompiled. Java Is Dynamic Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 33
- 34. Companion Website Characteristics of Java Java Is Simple Java Is Object-Oriented Java Is Distributed Java Is Interpreted Java Is Robust Java Is Secure Java Is Architecture-Neutral Java Is Portable Java‟s performance Because Java is architecture neutral, Java programs are Java's Performance portable. They can be run on any Java Is Multithreaded platform without being recompiled. Java Is Dynamic Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 34
- 35. Companion Website Characteristics of Java Java Is Simple Java Is Object-Oriented Java Is Distributed Java Is Interpreted Java Is Robust Java Is Secure Java Is Architecture-Neutral Java Is Portable Java's Performance Multithread programming is smoothly Java Is Multithreaded integrated in Java, whereas in other Java Is Dynamic languages you have to call procedures specific to the operating system to enable multithreading. Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 35
- 36. Companion Website Characteristics of Java Java Is Simple Java Is Object-Oriented Java Is Distributed Java Is Interpreted Java Is Robust Java Is Secure Java Is Architecture-Neutral Java Is Portable Java's Performance Java was designed to adapt to an evolving environment. New code can be loaded on the Java Is Multithreaded fly without recompilation. There is no need for developers to create, and for users to install, Java Is Dynamic major new software versions. New features can be incorporated transparently as needed. Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 36
- 37. JDK Versions JDK 1.02 (1995) JDK 1.1 (1996) JDK 1.2 (1998) JDK 1.3 (2000) JDK 1.4 (2002) JDK 1.5 (2004) a. k. a. JDK 5 or Java 5 JDK 1.6 (2006) a. k. a. JDK 6 or Java 6 JDK 1.7 (2011) a. k. a. JDK 7 or Java 7 Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 37
- 38. JDK Editions Java Standard Edition (J2SE) – J2SE can be used to develop client-side standalone applications or applets. Java Enterprise Edition (J2EE) – J2EE can be used to develop server-side applications such as Java servlets, Java ServerPages, and Java ServerFaces. Java Micro Edition (J2ME). – J2ME can be used to develop applications for mobile devices such as cell phones. This book uses J2SE to introduce Java programming. Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 38
- 39. Popular Java IDEs NetBeans Eclipse Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 39
- 40. A Simple Java Program Listing 1.1 //This program prints Welcome to Java! public class Welcome { public static void main(String[] args) { System.out.println("Welcome to Java!"); } } IMPORTANT NOTE: (1) To enable the buttons, you must Welcome download the entire slide file slide.zip and unzip the files into a directory (e.g., c:slide) . (2) You must have installed Run JDK and set JDK‟s bin directory in your environment path (e.g., c:Program Filesjavajdk1.7.0bin in your environment path. (3) If you are using Office 2010, check PowerPoint2010.doc located in the same folder with this ppt file. Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 40
- 41. Creating and Editing Using NotePad To use NotePad, type notepad Welcome.java from the DOS prompt. Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 41
- 42. Creating and Editing Using WordPad To use WordPad, type write Welcome.java from the DOS prompt. Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 42
- 43. Creating, Compiling, and Running Programs Create/Modify Source Code Source code (developed by the programmer) Saved on the disk public class Welcome { public static void main(String[] args) { System.out.println("Welcome to Java!"); Source Code } } Compile Source Code Byte code (generated by the compiler for JVM i.e., javac Welcome.java to read and interpret, not for you to understand) … Method Welcome() If compilation errors 0 aload_0 stored on the disk … Bytecode Method void main(java.lang.String[]) 0 getstatic #2 … 3 ldc #3 <String "Welcome to Java!"> 5 invokevirtual #4 … 8 return Run Byteode i.e., java Welcome Result Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 If runtime Education, Inc. All Pearson errors or incorrect result rights reserved. 43
- 44. Compiling Java Source Code You can port a source program to any machine with appropriate compilers. The source program must be recompiled, however, because the object program can only run on a specific machine. Nowadays computers are networked to work together. Java was designed to run object programs on any platform. With Java, you write the program once, and compile the source program into a special type of object code, known as bytecode. The bytecode can then run on any computer with a Java Virtual Machine, as shown below. Java Virtual Machine is a software that interprets Java bytecode. Java Bytecode Java Virtual Machine Any Computer Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 44
- 45. animation Trace a Program Execution Enter main method //This program prints Welcome to Java! public class Welcome { public static void main(String[] args) { System.out.println("Welcome to Java!"); } } Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 45
- 46. animation Trace a Program Execution Execute statement //This program prints Welcome to Java! public class Welcome { public static void main(String[] args) { System.out.println("Welcome to Java!"); } } Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 46
- 47. animation Trace a Program Execution //This program prints Welcome to Java! public class Welcome { public static void main(String[] args) { System.out.println("Welcome to Java!"); } } print a message to the console Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 47
- 48. Two More Simple Examples WelcomeWithThreeMessages Run ComputeExpression Run Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 48
- 49. Companion Website Supplements on the Companion Website See Supplement I.B for installing and configuring JDK See Supplement I.C for compiling and running Java from the command window for details www.cs.armstrong.edu/liang/intro8e Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 49
- 50. Companion Website Compiling and Running Java from the Command Window Set path to JDK bin directory – set path=c:Program Filesjavajdk1.6.0bin Set classpath to include the current directory – set classpath=. Compile – javac Welcome.java Run – java Welcome Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 50
- 51. Compiling and Running Java Companion Website from TextPad See Supplement II.A on the Website for details Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 51
- 52. Companion Website Compiling and Running Java from Eclipse See Supplement II.D on the Website for details Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 52
- 53. Companion Website Compiling and Running Java from NetBeans See Supplement I.D on the Website for details Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 53
- 54. Anatomy of a Java Program Class name Main method Statements Statement terminator Reserved words Comments Blocks Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 54
- 55. Class Name Every Java program must have at least one class. Each class has a name. By convention, class names start with an uppercase letter. In this example, the class name is Welcome. //This program prints Welcome to Java! public class Welcome { public static void main(String[] args) { System.out.println("Welcome to Java!"); } } Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 55
- 56. Main Method Line 2 defines the main method. In order to run a class, the class must contain a method named main. The program is executed from the main method. //This program prints Welcome to Java! public class Welcome { public static void main(String[] args) { System.out.println("Welcome to Java!"); } } Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 56
- 57. Statement A statement represents an action or a sequence of actions. The statement System.out.println("Welcome to Java!") in the program in Listing 1.1 is a statement to display the greeting "Welcome to Java!“. //This program prints Welcome to Java! public class Welcome { public static void main(String[] args) { System.out.println("Welcome to Java!"); } } Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 57
- 58. Statement Terminator Every statement in Java ends with a semicolon (;). //This program prints Welcome to Java! public class Welcome { public static void main(String[] args) { System.out.println("Welcome to Java!"); } } Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 58
- 59. Reserved words Reserved words or keywords are words that have a specific meaning to the compiler and cannot be used for other purposes in the program. For example, when the compiler sees the word class, it understands that the word after class is the name for the class. //This program prints Welcome to Java! public class Welcome { public static void main(String[] args) { System.out.println("Welcome to Java!"); } } Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 59
- 60. Blocks A pair of braces in a program forms a block that groups components of a program. public class Test { public static void main(String[] args) { Class block System.out.println("Welcome to Java!"); Method block } } Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 60
- 61. Special Symbols Character Name Description {} Opening and closing Denotes a block to enclose statements. braces () Opening and closing Used with methods. parentheses [] Opening and closing Denotes an array. brackets // Double slashes Precedes a comment line. " " Opening and closing Enclosing a string (i.e., sequence of characters). quotation marks ; Semicolon Marks the end of a statement. Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 61
- 62. { …} // This program prints Welcome to Java! public class Welcome { public static void main(String[] args) { System.out.println("Welcome to Java!"); } } Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 62
- 63. ( … ) // This program prints Welcome to Java! public class Welcome { public static void main(String[] args) { System.out.println("Welcome to Java!"); } } Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 63
- 64. ; // This program prints Welcome to Java! public class Welcome { public static void main(String[] args) { System.out.println("Welcome to Java!"); } } Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 64
- 65. // … // This program prints Welcome to Java! public class Welcome { public static void main(String[] args) { System.out.println("Welcome to Java!"); } } Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 65
- 66. "…" // This program prints Welcome to Java! public class Welcome { public static void main(String[] args) { System.out.println("Welcome to Java!"); } } Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 66
- 67. Displaying Text in a Message Dialog Box you can use the showMessageDialog method in the JOptionPane class. JOptionPane is one of the many predefined classes in the Java system, which can be reused rather than “reinventing the wheel.” WelcomeInMessageDialogBox Run IMPORTANT NOTE: (1) To enable the buttons, you must download the entire slide file slide.zip and unzip the files into a directory (e.g., c:slide) . (2) You must have installed JDK and set JDK‟s bin directory in your environment path (e.g., c:Program Filesjavajdk1.7.0bin in your environment path. (3) If you are using Office 2010, check PowerPoint2010.doc located in the same folder with this ppt file. Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 67
- 68. The showMessageDialog Method JOptionPane.showMessageDialog(null, "Welcome to Java!", "Display Message", JOptionPane.INFORMATION_MESSAGE); Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 68
- 69. Two Ways to Invoke the Method There are several ways to use the showMessageDialog method. For the time being, all you need to know are two ways to invoke it. One is to use a statement as shown in the example: JOptionPane.showMessageDialog(null, x, y, JOptionPane.INFORMATION_MESSAGE); where x is a string for the text to be displayed, and y is a string for the title of the message dialog box. The other is to use a statement like this: JOptionPane.showMessageDialog(null, x); where x is a string for the text to be displayed. Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 69
- 70. Programming Style and Documentation Appropriate Comments Naming Conventions Proper Indentation and Spacing Lines Block Styles Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 70
- 71. Appropriate Comments Include a summary at the beginning of the program to explain what the program does, its key features, its supporting data structures, and any unique techniques it uses. Include your name, class section, instructor, date, and a brief description at the beginning of the program. Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 71
- 72. Naming Conventions Choose meaningful and descriptive names. Class names: – Capitalize the first letter of each word in the name. For example, the class name ComputeExpression. Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 72
- 73. Proper Indentation and Spacing Indentation – Indent two spaces. Spacing – Use blank line to separate segments of the code. Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 73
- 74. Block Styles Use end-of-line style for braces. Next-line public class Test style { public static void main(String[] args) { System.out.println("Block Styles"); } } End-of-line style public class Test { public static void main(String[] args) { System.out.println("Block Styles"); } } Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 74
- 75. Programming Errors Syntax Errors – Detected by the compiler Runtime Errors – Causes the program to abort Logic Errors – Produces incorrect result Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 75
- 76. Syntax Errors public class ShowSyntaxErrors { public static main(String[] args) { System.out.println("Welcome to Java); } } Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 76
- 77. Runtime Errors public class ShowRuntimeErrors { public static void main(String[] args) { System.out.println(1 / 0); } } Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 77
- 78. Logic Errors public class ShowLogicErrors { public static void main(String[] args) { System.out.println("Celsius 35 is Fahrenheit degree "); System.out.println((9 / 5) * 35 + 32); } } Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 78