Ubuntu 安裝或移除 JDK

安裝：

1. 從官網下載JDK，.tar.gz 的版本
2. sudo mv ./jdk1.7.0_xx /usr/lib/jvm/jdk1.7.0 //將 jdk1.7.0_xx 資料夾移到 /usr/lib
3. Run：
   sudo update-alternatives --install "/usr/bin/java" "java" "/usr/lib/jvm/jdk1.7.0/bin/java" 1
   sudo update-alternatives --install "/usr/bin/javac" "javac" "/usr/lib/jvm/jdk1.7.0/bin/javac" 1
   sudo update-alternatives --install "/usr/bin/javaws" "javaws" "/usr/lib/jvm/jdk1.7.0/bin/javaws" 1
4. 選擇預設Java：
   sudo update-alternatives --config javac
   sudo update-alternatives --config javaws
5. 
   sudo update-alternatives --config java
6. java -version //檢查java版本
7. 開啟firefox plugin
   32 bit:
   sudo ln -s /usr/lib/jvm/jdk1.7.0/jre/lib/i386/libnpjp2.so /usr/lib/mozilla/plugins
   
   64 bit:sudo ln -s /usr/lib/jvm/jdk1.7.0/jre/lib/amd64/libnpjp2.so /usr/lib/mozilla/plugins

移除：

1. Run：
   sudo update-alternatives --remove "javac" "/usr/lib/jvm/jdk1.7.0/bin/javac"
   sudo update-alternatives --remove "java" /usr/lib/jvm/jdk1.7.0/bin/java"
   sudo update-alternatives --remove "javaws" "/usr/lib/jvm/jdk1.7.0/bin/javaws"
2. 移除plugin：
   sudo rm /usr/lib/mozilla/plugins/libnpjp2.so

==
from:
http://www.devsniper.com/ubuntu-12-04-install-sun-jdk-6-7/
http://www.devsniper.com/how-to-update-sun-jdk-7-on-ubuntu-12-04/