Ubuntu: installing java

- Install java JDK and JRE
apt-get install sun-java6-jdk sun-java6-jre

Do you want to continue [Y/n]? y
Get:1 http://my.archive.ubuntu.com hardy/main java-common 0.28ubuntu3 [78.2kB]
Get:2 http://my.archive.ubuntu.com hardy/multiverse sun-java6-jre 6-06-0ubuntu1 [6334kB]
Get:3 http://my.archive.ubuntu.com hardy/main odbcinst1debian1 2.2.11-16build1 [66.2kB]
Get:4 http://my.archive.ubuntu.com hardy/main unixodbc 2.2.11-16build1 [289kB]
Get:5 http://my.archive.ubuntu.com hardy/multiverse sun-java6-bin 6-06-0ubuntu1 [27.3MB]
Get:6 http://my.archive.ubuntu.com hardy/multiverse sun-java6-jdk 6-06-0ubuntu1 [9625kB]
85% [6 sun-java6-jdk 3208002/9625kB 33%]

- The final instalation directory is  /usr/lib/jvm/java-6-sun-1.6.0.06
- Ubuntu help to create a java symbolic link and put in /usr/bin for shortcut access
- type java -version to verify.

Post-Installation Setup

Set JAVA_HOME into environment variable

Copy following statement and append to the end of /etc/profile or .bashrc file, make system set JAVA_HOME into system environment variable:

export JAVA_HOME="/usr/lib/jvm/java-6-sun-1.6.0.06"

Source:
http://www.mkyong.com/java/how-to-install-java-jdk-on-ubuntu-linux/