install sun java in ubuntu

1. 下载：

http://www.oracle.com/technetwork/java/javase/downloads/jdk7-downloads-1880260.html

2. 解压安装：

sudo tar zxvf ./jdk-7u45-linux-x64.tar.gz  -C /usr/lib/jvm  
cd /usr/lib/jvm  
sudo mv jdk1.7.0_45/ java-7-sun  

3. 环境变量：

export JAVA_HOME=/usr/lib/jvm/java-7-sun  
export JRE_HOME=${JAVA_HOME}/jre  
export CLASSPATH=.:${JAVA_HOME}/lib:${JRE_HOME}/lib  
export PATH=${JAVA_HOME}/bin:$PATH

4. 配置默认：

sudo update-alternatives --install /usr/bin/java java /usr/lib/jvm/java-7-sun/bin/java 300  
sudo update-alternatives --install /usr/bin/javac javac /usr/lib/jvm/java-7-sun/bin/javac 300  
sudo update-alternatives --install /usr/bin/jar jar /usr/lib/jvm/java-7-sun/bin/jar 300   
sudo update-alternatives --install /usr/bin/javah javah /usr/lib/jvm/java-7-sun/bin/javah 300   
sudo update-alternatives --install /usr/bin/javap javap /usr/lib/jvm/java-7-sun/bin/javap 300   

sudo update-alternatives --config java  

参考：http://blog.csdn.net/snowdream86/article/details/6677450