Set JAVA_HOME / PATH

for single user

Login to your account and open .bash_profile file
$ vi ~/.bash_profile

Set JAVA_HOME as follows using syntax export JAVA_HOME=. If your path is set to /usr/java/jdk1.5.0_07/bin/java, set it as follows:
export JAVA_HOME=/usr/java/jdk1.5.0_07/bin/java

Set PATH as follows:
export PATH=$PATH:/usr/java/jdk1.5.0_07/bin

Save and close the file. Just logout and login back to see new changes:
$ echo $JAVA_HOME
$ echo $PATH

Tip: Use the following command to find out exact path to which java executable under UNIX / Linux:
$ which java

Please note that the file ~/.bashrc is similar, with the exception that ~/.bash_profile runs only for Bash login shells and .bashrc runs for every new Bash shell.

Set JAVA_HOME / PATH for all user

You need to setup global config in /etc/profile OR /etc/bash.bashrc file for all users:
# vi /etc/profile

Next setup PATH / JAVA_PATH variables as follows:
export PATH=$PATH:/usr/java/jdk1.5.0_07/bin
export PATH=$PATH:/usr/java/jdk1.5.0_07/bin