Introduction

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What is Java?
1.It is Object Oriented Programming Language.
2.It is platform independent.
3.It has automatic memory management.

What is Object Oriented Programming?
It has 5 properties.
1.Abstraction
2.Encapsulation
3.Inheritance
3.Modularity
5.Polymorphism

What are the things you need to run a java program?
1.JDK software
(available in http://java.sun.com/javase/downloads/index_jdk5.jsp)
2.Set the environmental variables

How to set the environmental variables?
There are two methods.
First Method:
1.Right click on My Computer,and select properties.
2.Select the Advanced tab.
3.Click on Environmental variables button on the bottom.
4.In the System Variables, click on New button.
5.Set Variable Name : CLASSPATH
Variable Value :C:\jdk1.5\lib;
and click OK.
6.Again click New Button.
7.Set Variable Name : PATH
Variable Value :C:\jdk1.5\bin;
and click OK.

Second Method:
1.Goto command prompt and navigate to the corresponding folder.
2.set path=c:\jdk1.5\bin;
3.set classpath=c:\jdk1.5\lib;.;

How to write a java program?
1.Open Notepad
2.Write the program
3.Save it with .java extension

Important things to be noted while writing a Java Program
1.Java is case sensitive.
2.Be careful with the filenames,it should match with the class names(case).
3.There should semicolon after every statement.



General Structure of a Java program
public class CLASSNAME
{
  public void METHODNAME()
  {
    //method body
  }
  public static void main(String args[])
  {
    //body
  }
}

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Small Programs

Hello World

public class HelloWorld{   public static void main(String args[]){     System.out.println("Hello World");   } }

c:\>java HelloWorld Hello World

Command Line Arguments

public class CmdArgs{   public static void main(String args[]){     System.out.println("The first argument is " + args[0]);   } }

c:\>java CmdArgs Hello Hello

Usage of If-else

public class ExIf{   public static void main(String args[]){     if(args[0].equals("args")){       System.out.println("You entered args");     }     else{       System.out.println("You did not enter args");     }   } }

c:\>java ExIf args You entered args

Usage of For loop

public class ExFor{   public static void main(String args[]){     for(int i=1;i<=args.length;i++){       System.out.println("The " + i + "th argument is " + args[i-1]);     }   } }

c:\>java ExFor One Two Three The 1th argument is One The 2th argument is Two The 3th argument is Three

Usage of while loop

public class ExWhile{   public static void main(String args[]){     int i=1;     while(i<=args.length){       System.out.println("The " + i + "th argument is " + args[i-1]);       i++;     }   } }

c:\>java ExWhile One Two Three The 1th argument is One The 2th argument is Two The 3th argument is Three