jdk 安装

1。下载jdk
2。sudo mkdir -p /usr/lib/jvm ; sudo mv ~/Downloads/jdk1.7.0_80 /usr/lib/jvm/
3.vim /etc/profile
在文件末尾添加下面内容
export JAVA_HOME=/usr/lib/jvm/jdk1.7.0_80
export JRE_HOME=/usr/lib/jvm/jdk1.7.0_80/jre
export CLASSPATH=.:$JAVA_HOME/lib/dt.jar:$JAVA_HOME/lib/tools.jar:$JAVA_HOME/lib:$JRE_HOME/lib:$CLASSPATH
export PATH=$JAVA_HOME/bin:$PATH

4。java -version 测试 输出如下 则安装成功

java version "1.7.0_80"
Java(TM) SE Runtime Environment (build 1.7.0_80-b15)
Java HotSpot(TM) 64-Bit Server VM (build 24.80-b11, mixed mode)
----------------------下面的没试----------------
到此，已经将oracle jdk配置完成。如果之前系统里面已经安装了openjdk，可以使用如下方法将默认jdk更改过来：
将系统默认的jdk修改过来
    $ sudo update-alternatives --install /usr/bin/java java /usr/lib/jvm/jdk1.7.0_80/bin/java 300

输入sun jdk前的数字就好了

    $ sudo update-alternatives --install /usr/bin/javac javac /usr/lib/jvm/jdk1.7.0_80/bin/javac 300

    $ sudo update-alternatives --config java
    $ sudo update-alternatives --config javac

---------------------------------------------open jdk 1.8 安装---------------------------
下载：https://download.csdn.net/download/iterjiay/9878121
csdn 下载 包，解压如下：
openjdk-8-jdk_8u91-b14-0ubuntu4~14.04_amd64.deb          
openjdk-8-jre_8u91-b14-0ubuntu4~14.04_amd64.deb
openjdk-8-jdk-headless_8u91-b14-0ubuntu4~14.04_amd64.deb 
openjdk-8-jre-headless_8u91-b14-0ubuntu4~14.04_amd64.deb

# dpkg -i openjdk-8-jre-headless_8u91-b14-0ubuntu4~14.04_amd64.deb
# dpkg -i openjdk-8-jre_8u91-b14-0ubuntu4~14.04_amd64.deb

openjdk version "1.8.0_91"
OpenJDK Runtime Environment (build 1.8.0_91-8u91-b14-0ubuntu4~14.04-b14)
OpenJDK 64-Bit Server VM (build 25.91-b14, mixed mode)