What's the correct way of installing jdk on linux

You can install and stay up to date with the latest Oracle Java 7 and all you have to do is manually add the PPA repository to the Software Sources.

From http://www.webupd8.org/2012/06/how-to-install-oracle-java-7-in-debian.html:

su -
echo "deb http://ppa.launchpad.net/webupd8team/java/ubuntu precise main" | tee -a     /etc/apt/sources.list
echo "deb-src http://ppa.launchpad.net/webupd8team/java/ubuntu precise main" | tee -a /etc/apt/sources.list
apt-key adv --keyserver keyserver.ubuntu.com --recv-keys EEA14886
apt-get update
apt-get install oracle-java7-installer
exit

For Ubuntu, http://www.webupd8.org/2012/01/install-oracle-java-jdk-7-in-ubuntu-via.html. With this, I've managed to installed JDK on my ubuntu server.

Step 1: Open Applicaction>> Accessories>> Terminal

Step 2: Type commandline as below...

  sudo apt-get install openjdk-6-jdk

Step 3: Type commandline as below...

  apt-cache search jdk

(Note: openjdk-6-jdk is symbolically used here you can choose jdk version as per your requirment.)

How to set "Environment Variables" for "Open jdk" in Ubuntu(Linux)?

Step 4: For "JAVA_HOME" (Environment Variable) type command as shown below, in "Terminal" using your installation path...

  export JAVA_HOME=/usr/lib/jvm/java-6-openjdk

(Note: "/usr/lib/jvm/java-6-openjdk" is symbolically used here just for demostration you should use your path as per your installation.)

Step 5: For "PATH" (Environment Variable) type command as shown below, in "Terminal" using your installation path...

  export PATH=/usr/lib/jvm/java-6-openjdk/bin

(Note: "/usr/lib/jvm/java-6-openjdk" is symbolically used here just for demostration you should use your path as per your installation.)

Step 6: Check for "open jdk" installation, just type command in "Terminal" as shown below java

Just make a symlink /usr/lib/jvm/jdk that points to /usr/lib/jvm/jdk<version>. Then all you have to do after updating the JDK is update the symlink to point to the new location.