1、去官网下载JDK

2、root权限并解压，复制到/usr/lib/jvm

sudo su

tar -zxvf jdk-7u21-linux-i586.tar.gz

mv jdk1.7.0_21/ /usr/lib/jvm

3、配置环境变量

gedit ~/.bashrc

在末尾添加

export JAVA_HOME=/usr/lib/jvm/jdk1.7.0_21

export JRE_HOME=${JAVA_HOME}/jre

export CLASSPATH=.:${JAVA_HOME}/lib:${JRE_HOME}/lib

export PATH=${JAVA_HOME}/bin:$PATH

立即生效：source ~/.bashrc

4、配置默认JDK

sudo update-alternatives --install /usr/bin/java java /usr/lib/jvm/jdk1.7.0_21/bin/java 300 

sudo update-alternatives --install /usr/bin/javac javac /usr/lib/jvm/jdk1.7.0_21/bin/javac 300 

sudo update-alternatives --install /usr/bin/jar jar /usr/lib/jvm/jdk1.7.0_21/bin/jar 300

检查

sudo update-alternatives --config java 

5、查看java版本号

命令行：

java -version

java version "1.7.0_21"

Java(TM) SE Runtime Environment (build 1.7.0_21-b11)

Java HotSpot(TM) Server VM (build 23.21-b01, mixed mode)