1.LINUX-JDK安裝
環境：CentOS 7.6 64位
1.1 1.8版本openjdk安裝
查看當前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
他們分別是 JRE 和 JDK，根據你的需求安裝即可
java-1.8.0-openjdk.x86_64 : OpenJDK Runtime Environment
java-1.8.0-openjdk-devel.x86_64 : OpenJDK Development Environment
安裝對應版本
[root@VM_0_9_centos ~]# sudo yum install java-1.8.0-openjdk-devel.x86_64 -y
查詢openjdk安裝路徑
[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卸載
1.查找卸載OpenJDK安裝包
[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
#卸載
[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安裝
環境：win10
進行java開發，首先要安裝jdk，安裝了jdk後還要進行環境變量配置：
1、下載jdk（http://www.oracle.com/technetwork/java/javase/downloads/jdk8-downloads-2133151.html），我下載的版本是：jdk-8u151-windows-x64.exe
2、安裝jdk-8u151-windows-x64.exe
3、配置環境變量：右擊“我的電腦”–>“高級”–>“環境變量”
1）在系統變量裏新建JAVA_HOME變量，變量值爲：C:\Program Files\Java\jdk1.8.0_14（根據自己的安裝路徑填寫）
2）新建classpath變量，變量值爲：.;%JAVA_HOME%\lib;%JAVA_HOME%\lib\tools.jar
3）在path變量（已存在不用新建）添加變量值：%JAVA_HOME%\bin;%JAVA_HOME%\jre\bin（注意變量值之間用“;”隔開）
注意：win10系統用絕對路徑：
4、“開始”–>“運行”–>輸入“javac”–>“Enter”，如果能正常打印用法說明配置成功！
補充環境變量的解析:path= C:\ProgramFiles\Java\jdk1.8.0_67\bin;C:\Program Files\Java\jdk1.8.0_67\bin\jre\bin;
JAVA_HOME:jdk的安裝路徑
classpath:java加載類路徑，只有類在classpath中java命令才能識別，在路徑前加了個"."表示當前路徑。
path：系統在任何路徑下都可以識別java,javac命令。
