Download Java SDK for ubuntu

For Oracle-JDK,

Step1)

Remove the OpenJDK
sudo apt-get purge openjdk*

Step2)

sudo apt-get install software-properties-common

sudo add-apt-repository ppa:webupd8team/java

sudo apt-get update

Step3)

Step3a) For JAVA8, sudo apt-get install oracle-java8-installer

Step3b) For JAVA7, sudo apt-get install oracle-java7-installer

Step3c) For JAVA6, sudo apt-get install oracle-java6-installer   

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For Open-JDK, 

$ sudo add-apt-repository "deb http://archive.canonical.com/ lucid partner"
$ sudo apt-get update
$ sudo apt-get install openjdk-6-jdk

openjdk-6-jdk 

openjdk-7-jdk