一、查看是否自带JDK
    java -version

    [root@lozzcomputers /]# java -version
    openjdk version “1.8.0_242”
    OpenJDK Runtime Environment (build 1.8.0_242-b08)
    OpenJDK 64-Bit Server VM (build 25.242-b08, mixed mode)
    二、查看文件
    rpm -qa | grep java

    [root@lozzcomputers /]# rpm -qa | grep java
    javapackages-tools-3.4.1-11.el7.noarch
    java-1.8.0-openjdk-1.8.0.242.b08-1.el7.x86_64
    tzdata-java-2019c-1.el7.noarch
    java-1.8.0-openjdk-headless-1.8.0.242.b08-1.el7.x86_64
    java-1.7.0-openjdk-1.7.0.251-2.6.21.1.el7.x86_64
    java-1.7.0-openjdk-headless-1.7.0.251-2.6.21.1.el7.x86_64
    python-javapackages-3.4.1-11.el7.noarch
    三、删除文件
    rpm -e —nodeps java-1.8.0-openjdk-1.8.0.242.b08-1.el7.x86_64
    rpm -e —nodeps java-1.8.0-openjdk-headless-1.8.0.242.b08-1.el7.x86_64
    rpm -e —nodeps java-1.7.0-openjdk-1.7.0.251-2.6.21.1.el7.x86_64
    rpm -e —nodeps java-1.7.0-openjdk-headless-1.7.0.251-2.6.21.1.el7.x86_64
    四、核查JDK是否存在
    [root@lozzcomputers /]# java -version
    -bash: /usr/bin/java: No such file or directory
    五、解压jdk-8u301-linux-x64.tar.gz
    tar -xf a.tar #解压tar包

    cd opt
    tar -xf jdk-8u301-linux-x64.tar.gz
    六、配置环境变量并保存文件
    vim /etc/profile
    #java environment
    export JAVA_HOME=/opt/jdk1.8.0_301
    export CLASSPATH=.:${JAVA_HOME}/jre/lib/rt.jar:${JAVA_HOME}/lib/dt.jar:${JAVA_HOME}/lib/tools.jar
    export PATH=$PATH:${JAVA_HOME}/bin
    七、刷新环境配置
    source /etc/profile
    八、查看是否安装成功
    [root@192 opt]# java -version
    java version “1.8.0_301”
    Java(TM) SE Runtime Environment (build 1.8.0_301-b09)
    Java HotSpot(TM) 64-Bit Server VM (build 25.301-b09, mixed mode)