apt-get install jdk

怕忘记，记录下：

sudo apt-get install python-software-properties
sudo add-apt-repository ppa:webupd8team/java
apt-get install software-properties-common 
sudo apt-get update

Oracle JDK 6(旧版本)
sudo apt-get install oracle-java6-installer
Oracle JDK 7(较新的稳定版本)
sudo apt-get install oracle-java7-installer
Oracle JDK 8(最新预览版本)
sudo apt-get install oracle-java8-installer