sudo apt-get update查看存在的版本
apt-cache madison openjdk-8-jdk
 but 8u292-b10-0ubuntu1~20.04 is to be installed
Depends: openjdk-8-jdk-headless (= 8u252-b09-1ubuntu1) but 8u292-b10-0ubuntu1~20.04 is to be installed
(以我安装的 8u252-b09-1ubuntu1 为例)
sudo apt-get install openjdk-8-jre-headless=8u252-b09-1ubuntu1 sudo apt-get install openjdk-8-jre=8u252-b09-1ubuntu1 sudo apt-get install openjdk-8-jdk-headless=8u252-b09-1ubuntu1 sudo apt-get install openjdk-8-jdk=8u252-b09-1ubuntu1配置java环境，全局配置在 /etc/profile
vim /etc/profile
export JAVA_HOME=/usr/lib/jvm/java-8-openjdk-amd64 export CLASSPATH=.:$JAVA_HOME/lib/dt.jar:$JAVA_HOME/lib/tools.jar export PATH=$JAVA_HOME/bin:$PATH
#可以通过echo $PATH查看是否生效，如果想还原PATH，可以执行
source /etc/environment验证 JDK 安装
java javac java -version
