How to install Sun JDK on Ubuntu

sudo apt-get install sun-java6-bin sun-java6-jre sun-java6-jdk

sudo update-java-alternatives -s java-6-sun

You also need to edit a file called /etc/jvm. This file defines the default system JVM search order. Each JVM should list their JAVA_HOME compatible directory in this file. The default system JVM is the first one available from top to bottom. Open /etc/jvm

$ sudo vi /etc/jvm

Make sure /usr/lib/jvm/java-6-sun is added to the top of JVM list

/usr/lib/jvm/java-6-sun

At the end your file should read as follows:

/usr/lib/jvm/java-6-sun
/usr/lib/jvm/java-gcj
/usr/lib/jvm/ia32-java-1.5.0-sun
/usr/lib/jvm/java-1.5.0-sun
/usr

Save and close the file.

Setup the environment variable

You also need to setup JAVA_HOME and PATH variable. Open your $HOME/.bash_profile or /etc/profile (system wide) configuration. Open your .bash_profile file:

$ vi $HOME/.bash_profile

Append following line:

export JAVA_HOME=/usr/lib/jvm/java-6-sun
 export PATH=$PATH:$JAVA_HOME/bin

Save and close the file.

Test your new JDK

Type the following command to display version:

$ java -version

Output:

java version "1.6.0_03"
Java(TM) SE Runtime Environment (build 1.6.0_03-b05)
Java HotSpot(TM) Server VM (build 1.6.0_03-b05, mixed mode)

Try HelloWorld.java - first java program

$ vi HelloWorld.java

Append code:

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

Save and close the file. Compile HelloWorld.java and execute program by typing following two instructions:

$ javac HelloWorld.java
 $ java  HelloWorld
 

Output:

Hello, World!