1.在Linux中安装JDK，检测是否安装成功，数据java -version 报错 如下
root@xiong-virtual-machine:/# java -version
程序 'java' 已包含在下列软件包中：
* default-jre
* gcj-5-jre-headless
* openjdk-8-jre-headless
* gcj-4.8-jre-headless
* gcj-4.9-jre-headless
* openjdk-9-jre-headless请尝试：apt install <选定的软件包>
2.解决办法：
红色颜色标注为jdk安装目录
sudo update-alternatives --install /usr/bin/java java /usr/java/jdk1.7.0_79/bin/java 300
sudo update-alternatives --install /usr/bin/javac javac /usr/java/jdk1.7.0_79/bin/javac 300
sudoupdate-alternatives --config java
3.输入java -version 安装jdk成功
xiong@xiong-virtual-machine:/$ java -version
java version "1.7.0_79"
Java(TM) SE Runtime Environment (build 1.7.0_79-b15)
Java HotSpot(TM) 64-Bit Server VM (build 24.79-b02, mixed mode)
xiong@xiong-virtual-machine:/$