大家好，又见面了，我是你们的朋友全栈君。

卸载

查看已经安装的jdk

[root@bogon jre]# rpm -qa|grep jdk
java-1.8.0-openjdk-headless-1.8.0.65-3.b17.el7.x86_64
java-1.7.0-openjdk-1.7.0.91-2.6.2.3.el7.x86_64
java-1.7.0-openjdk-headless-1.7.0.91-2.6.2.3.el7.x86_64
java-1.8.0-openjdk-1.8.0.65-3.b17.el7.x86_64

卸载命令

[root@bogon jre]# yum -y remove java-1.8.0-openjdk-headless-1.8.0.65-3.b17.el7.x86_64

卸载完成之后Java命令不被识别

[root@bogon lib]# java -version
bash: java: command not found...

安装

去官网下载jdk：http://www.oracle.com/technetwork/java/javase/downloads/jdk8-downloads-2133151.html
解压到安装目录

[root@bogon software]# tar -zxvf jdk-8u101-linux-x64.tar.gz -C /usr/local/java/

安装完毕之后在/etc/profile文件末尾添加

[root@bogon software]# vim /etc/profile
export JAVA_HOME=/usr/local/java/jdk1.8.0_101
export JRE_HOME=${JAVA_HOME}/jre
export CLASSPATH=.:${JAVA_HOME}/lib:${JRE_HOME}/lib
export PATH=${JAVA_HOME}/bin:$PATH

使/etc/profile生效

[root@bogon jdk1.8.0_101]# source /etc/profile

检测安装是否成功

[root@bogon jdk1.8.0_101]# java -version
java version "1.8.0_101"
Java(TM) SE Runtime Environment (build 1.8.0_101-b13)
Java HotSpot(TM) 64-Bit Server VM (build 25.101-b13, mixed mode)
[root@bogon jdk1.8.0_101]# javac
Usage: javac <options> <source files>
where possible options include:
  -g Generate all debugging info   -g:none Generate no debugging info   -g:{lines,vars,source} Generate only some debugging info   -nowarn Generate no warnings   -verbose Output messages about what the compiler is doing   -deprecation Output source locations where deprecated APIs are used   -classpath <path> Specify where to find user class files and annotation processors   -cp <path> Specify where to find user class files and annotation processors   -sourcepath <path> Specify where to find input source files   -bootclasspath <path> Override location of bootstrap class files   -extdirs <dirs> Override location of installed extensions   -endorseddirs <dirs> Override location of endorsed standards path   -proc:{none,only} Control whether annotation processing and/or compilation is done.   -processor <class1>[,<class2>,<class3>...] Names of the annotation processors to run; bypasses default discovery process   -processorpath <path> Specify where to find annotation processors   -parameters Generate metadata for reflection on method parameters   -d <directory> Specify where to place generated class files   -s <directory> Specify where to place generated source files   -h <directory> Specify where to place generated native header files   -implicit:{none,class} Specify whether or not to generate class files for implicitly referenced files   -encoding <encoding> Specify character encoding used by source files   -source <release> Provide source compatibility with specified release   -target <release> Generate class files for specific VM version   -profile <profile> Check that API used is available in the specified profile   -version Version information   -help Print a synopsis of standard options   -Akey[=value] Options to pass to annotation processors   -X Print a synopsis of nonstandard options   -J<flag> Pass <flag> directly to the runtime system   -Werror Terminate compilation if warnings occur   @<filename>                Read options and filenames from file