Introduction

The Java Programming Language

Java Development Environment

Software Installation

Compilation Process

How to Compile and Run a Java Application

How to Compile and Run a Java Applet

The Java Programming Language

Objects

Reusable software components that model real-world items

Look all around you

People, animals, plants, cars, etc.

Attributes

Size, shape, color, weight, etc.

Behaviors (Methods)

Cars: forward, backward, turn, etc.

Object-Oriented Programming

Object-oriented design (OOD)

Models real-world objects

Models communication among objects

Encapsulates  data (attributes) and functions (behaviors)

Information hiding

Communication through well-defined interfaces

Object-oriented language

Programming is called  object-oriented programming  (OOP)

Java Programming Languages

Classes  are a fundamental concept in Java.

It role is as ‘factories’ for objects.

An object  is an entity that can be manipulated in a program.

All program statements are placed inside methods (functions or procedures).

A method is a collection of programming instructions for a particular task.

Java Class

Java Environment

Java programs normally undergo five phases

Edit

Programmer writes program and stores program on disk with extension .java

Compile

Compiler creates bytecodes from program and store a program in a file with extension .class

Load

Class loader stores bytecodes in memory

Execute (Interpret)

Interpreter translates bytecodes into machine language

Software Installation

Install Java 2 SDK
     Compiler : j2sdk1_4_2-win.exe
     Documentation: j2sdk1_4_2-doc.zip

Edit Autoexec.bat
SET PATH=c:\jdk1.4.2\bin;%PATH%
SET CLASSPATH= .;c:\working_directory

Compilation Process

**Figure from java.sun.com

How to Compile and Run a Java Application

Edit-Compile-Debug Loop
1. To Edit :

  - use any text editor such as Notepad
     - save source  code with extension .java
2. To Compile : use the command
     javac Hello.java
if no error, a file names “Hello.class” is created
3. To Run : use command

           java Hello
(java virtual machine)

Java Syntax

1.1 Simple Program
public class ClassName
{    public static void main(String[] args)
     {   statements
     }
}

1.2 Method Call
     object.methodName(parameters)
Example:   System.out.println(“Hi”);

A Simple Java Application

1.  // Example 1 : Hello Application

2.  // Hello.java

3. 

4.  public class Hello {

5.     public static void main(String args[]) {

6.             System.out.println(“Hello!”);

7.        }

8.     }

Java

Java is case-sensitive.

On line 4, the keyword “public” indicates that the class is usable by the “public”

The name of the public class must be the same as the file name

Line 5 defines a method called main

String[ ] args is a parameter that contains the command line arguments

Every statement must end with a semicolon

Method in a particular object can be called by

       class.object.method

For example:

       System.out.println

System.out.println(“Hello”) statement calls method println of object names System.out that prints “Hello”

“Hello” is a string which is enclosed insidedouble quotation marks

System.out.println(5 + 4);  // 9
9

System.out.println(“5 + 4”); // 5 + 4

   5 + 4

System.out.print(“Hello”); System.out.println(“Java”);
   HelloJava

Escape Sequences

To print
    Hello "Java"

Can’t use

   System.out.println("Hello "Java"");

Must use escape sequence (\)
System.out.println("Hello \"Java\"");

System.out.println("c:\\data\\a.txt"); will print

     c:\data\a.txt

\n starts a new line, for example:

   System.out.print(“A\nB\nC”); will print

        A

        B

        C

\t moves the screen cursor to the next tab stop

\r positions the cursor to the beginning of the current line

Import

To use classes from Java Class Library, we need to import those classes from a package in the library.

        import packageName.Classname;

Package is a collection of classes with a related purpose.

For example:

        import java.applet.applet;

A Simple Java Applet

  // Example 2: HelloApplet

   import java.applet.Applet;

   import java.awt.Graphics;

   public class HelloApplet extends Applet {

      public void paint(Graphics g) {

          g.drawString(“Hello !”, 25, 25);

      }

   }

How to Compile and Run a Java Applet

To Compile
     c:> javac HelloApplet.java

To Run an applet, we need  HelloApplet.html

<HTML>

<APPLET code=”HelloApplet.class”  width=500 height=300 </APPLET>

</HTML>

Then, To run this applet,
     c:> appletviewer HelloApplet.html
 or use any browsers, e.g. Netscape, Internet Explorer.