Java运用于执行java程序（java运行环境）
Javac运用于java程序编译（java程序开发环境）
步骤二：alternatives安装JDK
#alternatives --install /usr/bin/java java /usr/local/jdk版本/bin/java 1
#alternatives --install /usr/bin/javac java /usr/local/jdk版本/bin/javac 2
步骤二：查看可用的版本信息
#alternatives --display java
#alternatives --display javac
步骤三：切换java版本
#alternatives --config java
#alternatives --config javac
删除jdk版本（可选项，需要删除时使用--remove）
#alternatives --remove java /usr/local/java/jdk版本/bin
#alternatives --remove javac /usr/local/java/jdk版本/bin
步骤四：修改当前用户的jdk运行环境
#echo export JAVA_HOME=/usr/bin/java >>~/.bash_profile

echo export PATH=$PATH:$JAVA_HOME/bin >>~/.bash_profile

    # source ~/.bash_profile

注意需要注释掉/etc/profile文件里面的JAVA_HOM
查看及管理JAVA_HOME

echo $JAVA_HOME

/usr/local/jdk

java -version

java version "1.8.0_111"
Java(TM) SE Runtime Environment (build 1.8.0_111-b14)
Java HotSpot(TM) 64-Bit Server VM (build 25.111-b14, mixed mode)

#实例

[cqs@centos7 jdk]$echo ’export JAVA_HOME=/usr/bin/java’ >>~/.bash_profile
[cqs@centos7 jdk]$ echo ‘export PATH=$PATH:$JAVA_HOME/bin’ >>~/.bash_profile
[cqs@centos7 jdk]$ source ~/.bash_profile

注意需要注释掉/etc/profile文件里面的JAVA_HOM

[cqs@centos7 jdk]$ echo $JAVA_HOME

/usr/bin/java

[cqs@centos7 jdk]$ echo $PATH

/usr/local/bin:/usr/bin:/usr/local/mysql/bin:/usr/local/sbin:/usr/sbin:/home/cqs/.local/bin:/home/cqs/bin:/usr/bin/java/bin

步骤一：alternatives安装JDK1.7(链接路径【link】:/usr/bin/java  链接名【name】:java 应用程序JAVA实际路径【path】：/home/cqs/data/jdk/jdk1.7.0_80/bin/java  优先级【priority】 :1)
    [cqs@centos7 jdk]$ sudo alternatives --install /usr/bin/java java ~/data/jdk/jdk1.7.0_80/bin/java 1
    [cqs@centos7 jdk]$ sudo alternatives --config java

There is 1 program that provides 'java'.
Selection Command

*+ 1 /home/cqs/data/jdk/jdk1.7.0_80/bin/java
Enter to keep the current selection[+], or type selection number:

[cqs@centos7 jdk]$ java -version

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)

alternatives安装JDK1.8

[cqs@centos7 jdk]$ sudo alternatives --install /usr/bin/java java ~/data/jdk/jdk1.8.0_161/bin/java 2
[cqs@centos7 jdk]$ sudo alternatives --config java

There are 2 programs which provide 'java'.
Selection Command

• 1 /home/cqs/data/jdk/jdk1.7.0_80/bin/java

  • 2 /home/cqs/data/jdk/jdk1.8.0_161/bin/java
    Enter to keep the current selection[+], or type selection number: 2

  [cqs@centos7 jdk]$ java -version

  java version "1.8.0_161"
  Java(TM) SE Runtime Environment (build 1.8.0_161-b12)
  Java HotSpot(TM) 64-Bit Server VM (build 25.161-b12, mixed mode)
  [cqs@centos7 jdk]$ sudo alternatives --config java
  There are 2 programs which provide 'java'.
  Selection Command

  1 /home/cqs/data/jdk/jdk1.7.0_80/bin/java
  *+ 2 /home/cqs/data/jdk/jdk1.8.0_161/bin/java
  Enter to keep the current selection[+], or type selection number: 1

  [cqs@centos7 jdk]$ java -version

  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)