Install JDK on Ubuntu

1. openjdk
      $ sudo apt-get update
      $ sudo apt-get install openjdk-7-jdk

2. sun java
      http://askubuntu.com/questions/253039/how-can-i-uninstall-my-current-java-and-install-sun-java-1-6

3. 手動設定JDK
      http://lnmcc.net/2013/03/28/android%E7%BC%96%E8%AF%91%E9%94%99%E8%AF%AF-android-the-correct-version-is-1-6/

4. update the default Java version by running:
     $ sudo update-alternatives --config java
     $ sudo update-alternatives --config javac

     $ sudo update-java-alternatives -s <jname>