1.LINUX-JDK安装
环境：CentOS 7.6 64位
1.1 1.8版本openjdk安装
查看当前openjdk版本
[root@VM_0_9_centos ~]# sudo yum search jdk
copy-jdk-configs.noarch : JDKs configuration files copier
java-1.6.0-openjdk.x86_64 : OpenJDK Runtime Environment
java-1.6.0-openjdk-demo.x86_64 : OpenJDK Demos
java-1.6.0-openjdk-devel.x86_64 : OpenJDK Development Environment
java-1.6.0-openjdk-javadoc.x86_64 : OpenJDK API Documentation
java-1.6.0-openjdk-src.x86_64 : OpenJDK Source Bundle
java-1.7.0-openjdk.x86_64 : OpenJDK Runtime Environment
java-1.7.0-openjdk-accessibility.x86_64 : OpenJDK accessibility connector
java-1.7.0-openjdk-demo.x86_64 : OpenJDK Demos
java-1.7.0-openjdk-devel.x86_64 : OpenJDK Development Environment
java-1.7.0-openjdk-headless.x86_64 : The OpenJDK runtime environment without audio and video support
java-1.7.0-openjdk-javadoc.noarch : OpenJDK API Documentation
java-1.7.0-openjdk-src.x86_64 : OpenJDK Source Bundle
java-1.8.0-openjdk.i686 : OpenJDK Runtime Environment 8
java-1.8.0-openjdk.x86_64 : OpenJDK Runtime Environment 8
java-1.8.0-openjdk-accessibility.i686 : OpenJDK accessibility connector
java-1.8.0-openjdk-accessibility.x86_64 : OpenJDK accessibility connector
java-1.8.0-openjdk-accessibility-debug.i686 : OpenJDK 8 accessibility connector for packages with debug on
java-1.8.0-openjdk-accessibility-debug.x86_64 : OpenJDK 8 accessibility connector for packages with debug on
java-1.8.0-openjdk-debug.i686 : OpenJDK Runtime Environment 8 with full debug on
java-1.8.0-openjdk-debug.x86_64 : OpenJDK Runtime Environment 8 with full debug on
java-1.8.0-openjdk-demo.i686 : OpenJDK Demos 8
java-1.8.0-openjdk-demo.x86_64 : OpenJDK Demos 8
java-1.8.0-openjdk-demo-debug.i686 : OpenJDK Demos 8 with full debug on
java-1.8.0-openjdk-demo-debug.x86_64 : OpenJDK Demos 8 with full debug on
java-1.8.0-openjdk-devel.i686 : OpenJDK Development Environment 8
java-1.8.0-openjdk-devel.x86_64 : OpenJDK Development Environment 8
java-1.8.0-openjdk-devel-debug.i686 : OpenJDK Development Environment 8 with full debug on
java-1.8.0-openjdk-devel-debug.x86_64 : OpenJDK Development Environment 8 with full debug on
java-1.8.0-openjdk-headless.i686 : OpenJDK Headless Runtime Environment 8
java-1.8.0-openjdk-headless.x86_64 : OpenJDK Headless Runtime Environment 8
java-1.8.0-openjdk-headless-debug.i686 : OpenJDK Runtime Environment with full debug on
java-1.8.0-openjdk-headless-debug.x86_64 : OpenJDK Runtime Environment with full debug on
java-1.8.0-openjdk-javadoc.noarch : OpenJDK 8 API documentation
java-1.8.0-openjdk-javadoc-debug.noarch : OpenJDK 8 API documentation for packages with debug on
java-1.8.0-openjdk-javadoc-zip.noarch : OpenJDK 8 API documentation compressed in a single archive
java-1.8.0-openjdk-javadoc-zip-debug.noarch : OpenJDK 8 API documentation compressed in a single archive for packages with debug on
java-1.8.0-openjdk-src.i686 : OpenJDK Source Bundle 8
java-1.8.0-openjdk-src.x86_64 : OpenJDK Source Bundle 8
java-1.8.0-openjdk-src-debug.i686 : OpenJDK Source Bundle 8 for packages with debug on
java-1.8.0-openjdk-src-debug.x86_64 : OpenJDK Source Bundle 8 for packages with debug on
java-11-openjdk.i686 : OpenJDK Runtime Environment 11
java-11-openjdk.x86_64 : OpenJDK Runtime Environment 11
java-11-openjdk-debug.i686 : OpenJDK Runtime Environment 11 with full debug on
java-11-openjdk-debug.x86_64 : OpenJDK Runtime Environment 11 with full debug on
java-11-openjdk-demo.i686 : OpenJDK Demos 11
java-11-openjdk-demo.x86_64 : OpenJDK Demos 11
java-11-openjdk-demo-debug.i686 : OpenJDK Demos 11 with full debug on
java-11-openjdk-demo-debug.x86_64 : OpenJDK Demos 11 with full debug on
java-11-openjdk-devel.i686 : OpenJDK Development Environment 11
java-11-openjdk-devel.x86_64 : OpenJDK Development Environment 11
java-11-openjdk-devel-debug.i686 : OpenJDK Development Environment 11 with full debug on
java-11-openjdk-devel-debug.x86_64 : OpenJDK Development Environment 11 with full debug on
java-11-openjdk-headless.i686 : OpenJDK Headless Runtime Environment 11
java-11-openjdk-headless.x86_64 : OpenJDK Headless Runtime Environment 11
java-11-openjdk-headless-debug.i686 : OpenJDK Runtime Environment with full debug on
java-11-openjdk-headless-debug.x86_64 : OpenJDK Runtime Environment with full debug on
java-11-openjdk-javadoc.i686 : OpenJDK 11 API documentation
java-11-openjdk-javadoc.x86_64 : OpenJDK 11 API documentation
java-11-openjdk-javadoc-debug.i686 : OpenJDK 11 API documentation for packages with debug on
java-11-openjdk-javadoc-debug.x86_64 : OpenJDK 11 API documentation for packages with debug on
java-11-openjdk-javadoc-zip.i686 : OpenJDK 11 API documentation compressed in single archive
java-11-openjdk-javadoc-zip.x86_64 : OpenJDK 11 API documentation compressed in a single archive
java-11-openjdk-javadoc-zip-debug.i686 : OpenJDK 11 API documentation compressed in single archive for packages with debug on
java-11-openjdk-javadoc-zip-debug.x86_64 : OpenJDK 11 API documentation compressed in a single archive for packages with debug on
java-11-openjdk-jmods.i686 : JMods for OpenJDK 11
java-11-openjdk-jmods.x86_64 : JMods for OpenJDK 11
java-11-openjdk-jmods-debug.i686 : JMods for OpenJDK 11 with full debug on
java-11-openjdk-jmods-debug.x86_64 : JMods for OpenJDK 11 with full debug on
java-11-openjdk-src.i686 : OpenJDK Source Bundle 11
java-11-openjdk-src.x86_64 : OpenJDK Source Bundle 11
java-11-openjdk-src-debug.i686 : OpenJDK Source Bundle 11 for packages with debug on
java-11-openjdk-src-debug.x86_64 : OpenJDK Source Bundle 11 for packages with debug on
java-latest-openjdk.x86_64 : OpenJDK Runtime Environment 13
java-latest-openjdk-debug.x86_64 : OpenJDK Runtime Environment 13 with full debug on
java-latest-openjdk-demo.x86_64 : OpenJDK Demos 13
java-latest-openjdk-demo-debug.x86_64 : OpenJDK Demos 13 with full debug on
java-latest-openjdk-devel.x86_64 : OpenJDK Development Environment 13
java-latest-openjdk-devel-debug.x86_64 : OpenJDK Development Environment 13 with full debug on
java-latest-openjdk-headless.x86_64 : OpenJDK Headless Runtime Environment 13
java-latest-openjdk-headless-debug.x86_64 : OpenJDK Runtime Environment with full debug on
java-latest-openjdk-javadoc.x86_64 : OpenJDK 13 API documentation
java-latest-openjdk-javadoc-zip.x86_64 : OpenJDK 13 API documentation compressed in a single archive
java-latest-openjdk-jmods.x86_64 : JMods for OpenJDK 13
java-latest-openjdk-jmods-debug.x86_64 : JMods for OpenJDK 13 with full debug on
java-latest-openjdk-src.x86_64 : OpenJDK Source Bundle 13
java-latest-openjdk-src-debug.x86_64 : OpenJDK Source Bundle 13 for packages with debug on
他们分别是 JRE 和 JDK，根据你的需求安装即可
java-1.8.0-openjdk.x86_64 : OpenJDK Runtime Environment
java-1.8.0-openjdk-devel.x86_64 : OpenJDK Development Environment
安装对应版本
[root@VM_0_9_centos ~]# sudo yum install java-1.8.0-openjdk-devel.x86_64 -y
查询openjdk安装路径
[root@VM_0_9_centos /]# which java
/usr/bin/java
[root@VM_0_9_centos /]# echo $JAVA_HOME
[root@VM_0_9_centos /]# ls -lrt /usr/bin/java
lrwxrwxrwx 1 root root 22 Feb 4 11:55 /usr/bin/java -> /etc/alternatives/java
[root@VM_0_9_centos /]# ls -lrt /etc/alternatives/java
lrwxrwxrwx 1 root root 73 Feb 4 11:55 /etc/alternatives/java -> /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.242.b08-0.el7_7.x86_64/jre/bin/java
1.2 1.8版本openjdk卸载
1.查找卸载OpenJDK安装包
[root@VM_0_9_centos ~]# rpm -qa | grep openjdk
java-1.8.0-openjdk-headless-1.8.0.242.b08-0.el7_7.x86_64
java-1.8.0-openjdk-1.8.0.242.b08-0.el7_7.x86_64
#卸载
[root@VM_0_9_centos ~]# yum -y remove java-1.8.0-openjdk-headless-1.8.0.242.b08-0.el7_7.x86_64
2.WINDOWS-JDK安装
环境：win10
进行java开发，首先要安装jdk，安装了jdk后还要进行环境变量配置：
1、下载jdk（http://www.oracle.com/technetwork/java/javase/downloads/jdk8-downloads-2133151.html），我下载的版本是：jdk-8u151-windows-x64.exe
2、安装jdk-8u151-windows-x64.exe
3、配置环境变量：右击“我的电脑”–>“高级”–>“环境变量”
1）在系统变量里新建JAVA_HOME变量，变量值为：C:\Program Files\Java\jdk1.8.0_14（根据自己的安装路径填写）
2）新建classpath变量，变量值为：.;%JAVA_HOME%\lib;%JAVA_HOME%\lib\tools.jar
3）在path变量（已存在不用新建）添加变量值：%JAVA_HOME%\bin;%JAVA_HOME%\jre\bin（注意变量值之间用“;”隔开）
注意：win10系统用绝对路径：
4、“开始”–>“运行”–>输入“javac”–>“Enter”，如果能正常打印用法说明配置成功！
补充环境变量的解析:path= C:\ProgramFiles\Java\jdk1.8.0_67\bin;C:\Program Files\Java\jdk1.8.0_67\bin\jre\bin;
JAVA_HOME:jdk的安装路径
classpath:java加载类路径，只有类在classpath中java命令才能识别，在路径前加了个"."表示当前路径。
path：系统在任何路径下都可以识别java,javac命令。
