![1. // Your First Program
2. class HelloWorld
{
3. public static void
main(String[] args)
{
4.
System.out.println("Hello
, World!");
}
}
In line 1; In Java, any line starting
with // is a comment
In line 2; in the program, HelloWorld is
the name of the class, and the class
definition is: class helloworld
In line 3; This is the main method.
Every application in Java must contain
the main method. The Java compiler
starts executing the code from the
main method.
In line 4; The code above is a print
statement. It prints the text Hello,
World! to standard output (your
screen). The text inside the quotation
marks is called String in Java.](https://image.slidesharecdn.com/lecture1-updated-230127140454-5568741f/85/OOP-with-Java-16-320.jpg)
![Anatomy of a Java Program
Statements:
A statement represents an action or a sequence of actions. The statement
System.out.println(“Hello Java world!") in the program in Example is a statement
to display the greeting " Hello Java world! “. Every statement in Java ends with a
semicolon (;).
Blocks:
A pair of braces in a program forms a block that groups components of aprogram.
public class JavaApplication1 {
public static void main(String[] args) {
System.out.println("Hello Java World !");
}
}
Class block
Meth
CE&ME, NUST
od block](https://image.slidesharecdn.com/lecture1-updated-230127140454-5568741f/85/OOP-with-Java-19-320.jpg)
OOP with Java
- 1. CMP-2123 Object Oriented Programming OOP with Java Lecture # 1
- 2. History • In 1991, Java was developed by a team led by James Gosling and Sun Microsystems for use in embedded chips. • Sun microsystems was purchased by oracle (Oak) in 2010. • Java, May 20, 1995, Sun World, redesigned for web applications. • HotJava ( first Java-enabled Web browser )
- 3. Version History of Java
- 5. Features of Java • Java is simple • Java is object-oriented • Java is distributed • Java is interpreted • Java is robust • Java is secure • Java is portable • Java’s performance • Java is multithreaded • Java has garbage Collector
- 6. Java Features (1) Simple • fixes some clumsy features of C++ • no pointers • automatic garbage collection • rich pre-defined class library Object oriented • focus on the data (objects) and methods manipulating the data • all functions are associated with objects • almost all data types are objects (files, strings, etc.) • potentially better code organization and reuse
- 7. Java Features (2) Interpreted • java compiler generate byte-codes, not native machine code • the compiled byte-codes are platform-independent • java bytecodes are translated on the fly to machine readable instructions in runtime (Java Virtual Machine) Portable • same application runs on all platforms • the sizes of the primitive data types are always the same
- 8. Java Features (3) Reliable • extensive compile-time and runtime error checking • no pointers. Memory corruptions or unauthorized memory accesses are impossible • automatic garbage collection tracks objects usage over time Secure • usage in networked environments requires more security • memory allocation model is a major defense • access restrictions are forced (private, public)
- 9. Java Features (4) Multithreaded • multiple concurrent threads of executions can run simultaneously • utilizes a sophisticated set of synchronization primitives (based on monitors and condition variables paradigm) to achieve this
- 10. Java Disadvantages Slower than compiled language such as C • an experiment in 1999 showed that Java was 3 or 4 times slower than C or C++ • title of the article: “Comparing Java vs. C/C++ Efficiency Issues to Interpersonal Issues” (Lutz Prechelt) • adequate for all but the most time-intensive programs
- 11. 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 and Java ServerPages. • Java Micro Edition (J2ME). J2ME can be used to develop applications for mobile devices such as cell phones.
- 12. Java Applet • Java programs can be run from a Web browser. Such programs are called applets. Applets employ a modern graphical interface with buttons, text fields, text areas, radio buttons, and so on, to interact with users on the Web and process their requests. • You can use a Java development tool (e.g., NetBeans, Eclipse, and Text Pad)—software that provides an integrated development environment (IDE) for developing Java programs quickly.
- 13. Compile and Run
- 14. Creating..Compiling .. Executing Source Code Create/Modify Source Code Bytecode Run Byteode i.e. java Welcome Result Compile Source Code i.e. javac Welcome.java If compilation errors If runtime errors or incorrect result Java Interpreter on Windows Java Interpreter on Sun Solaris Java Interpreter on Linux Bytecode ...
- 15. Java is case sensitive
- 16. 1. // Your First Program 2. class HelloWorld { 3. public static void main(String[] args) { 4. System.out.println("Hello , World!"); } } In line 1; In Java, any line starting with // is a comment In line 2; in the program, HelloWorld is the name of the class, and the class definition is: class helloworld In line 3; This is the main method. Every application in Java must contain the main method. The Java compiler starts executing the code from the main method. In line 4; The code above is a print statement. It prints the text Hello, World! to standard output (your screen). The text inside the quotation marks is called String in Java.
- 17. Anatomy of a Java Program Comments: In Java, comments are preceded by two slashes (//) in a line, or enclosed between /* and */ in one or multiple lines. When the compiler sees //, it ignores all text after // in the same line. When it sees /*, it scans for the next */ and ignores any text between /* and */. Package : The second line in the program (package javaapplication1;) specifies a package name, javaapplication1, for the class javaapplication1. It compiles the source code in javaapplication1.java, generates javaapplication1.class, and stores javaapplication1.class in the javaapplication1 folder.
- 18. Anatomy of a Java Program 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. Other reserved words are public, static, and voidetc. Modifiers: Java uses certain reserved words called modifiers that specify the properties of the data, methods, and classes and how they can be used. Examples of modifiers are public and static. Other modifiers are private, final, abstract, and protected. A public datum, method, or class can be accessed by other programs through reserve words CE&ME, NUST
- 19. Anatomy of a Java Program Statements: A statement represents an action or a sequence of actions. The statement System.out.println(“Hello Java world!") in the program in Example is a statement to display the greeting " Hello Java world! “. Every statement in Java ends with a semicolon (;). Blocks: A pair of braces in a program forms a block that groups components of aprogram. public class JavaApplication1 { public static void main(String[] args) { System.out.println("Hello Java World !"); } } Class block Meth CE&ME, NUST od block
- 20. Assignment: Reserved word vs Modifiers Package vs libraries JVM version JVM vs JDK
Editor's Notes
- #17: The code above is a print statement. It prints the text Hello, World! to standard output (your screen). The text inside the quotation marks is called String in Java.
- #18: // This is a comment System.out.println("Hello World"); /* The code below will print the words Hello World to the screen, and it is amazing */ System.out.println("Hello World");