Ubuntu系统安装JAVA JDK7

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