参考：http://www.cnblogs.com/feng_013/archive/2012/08/14/2638729.html
PPA安装：
sudo add-apt-repository ppa:webupd8team/java
sudo apt-get update
sudo apt-get install oracle-java7-installer
千万不要用 否则会报错安装不了
sudo add-apt-repository ppa:eugenesan/java
如果已经用了可以：
sudo rm /var/lib/dpkg/info/oracle-java7-installer*
sudo apt-get purge oracle-java7-installer*
sudo rm /etc/apt/sources.list.d/*java*
sudo apt-get update
sudo add-apt-repository ppa:webupd8team/java
sudo apt-get update
sudo apt-get install oracle-java7-installer
参考：
http://askubuntu.com/questions/126372/sha256sum-mismatch-jdk-7u3-linux-x64-tar-gz-error-when-trying-to-install-orac
卸载：
sudo apt-get install ppa-purge
sudo ppa-purge ppa:upubuntu-com/java
sudo apt-get remove oracle-java7-installer
sudo apt-get update