December 2nd, 2012 
There are several JDK implementations available for Linux, such as Oracle JDK 7, OpenJDK, Sun JDK 6, IBM JDK and GNU Java Compiler. We shall choose the Oracle JDK 7 (Ubuntu chooses OpenJDK as its default JDK, which is not 100% compatible with Oracle JDK).
Step 1 : Check if JDK has already been Installed
Open a Terminal or press Ctrl + Alt + T and issue this command:
javac -version
If a JDK version number (e.g., "javac 1.7.0_{xx}") appears, JDK has already been installed. You can skip the installation and goto step 3.
Step 2 : Download and Install JDK
Goto JDK (Java SE) download site at
Select "Java SE 7ux" ⇒ JDK ⇒ Download ⇒ "Accept Licence Agreement" ⇒ Select Linux x86 (for 32-bit system) or Linux x64 (for 64-bit system) "tar.gz" package, e.g., "jdk-7ux-linux-i586.tar.gz". The tarball will be stored in folder "~/Downloads", by default.
We shall install JDK under "/usr/lib/jvm". First, create a directory "jvm" under "/usr/lib" (with superuser authority "sudo"). Open a Terminal and issue these commands:
cd /usr/lib
sudo mkdir jvm
