从 Java 8 开始，Oracle 开启了快速的更新模式，每半年都会发布一个版本更新。现在最新的版本是 Java 16，那么如何在 Ubuntu 中管理多个版本的 JDK 呢？
打开终端，输入 sudo add-apt-repository ppa:openjdk-r/ppa 命令添加软件源
$ sudo add-apt-repository ppa:openjdk-r/ppa
More info: https://launchpad.net/~openjdk-r/+archive/ubuntu/ppa
Press [ENTER] to continue or Ctrl-c to cancel adding it.
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Fetched 39.6 kB in 2s (21.2 kB/s)
Reading package lists... Done
复制代码输入 sudo apt-get update 升级系统软件包
$ sudo apt-get update
Hit:1 http://mirrors.tuna.tsinghua.edu.cn/ubuntu focal InRelease
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Reading package lists... Done
复制代码输入 sudo apt-get install openjdk-14-jdk 命令安装指定的 JDK 版本，在这里我选择的版本是 JDK14
$ sudo apt-get install openjdk-14-jdk
Reading package lists... Done
Building dependency tree
Reading state information... Done
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Processing triggers for hicolor-icon-theme (0.17-2) ...
Processing triggers for mime-support (3.64ubuntu1) ...
复制代码update-alternatives 命令可以管理多个版本的 JDK，如切换 JDK 版本：
$ sudo update-alternatives --config java
There are 3 choices for the alternative java (providing /usr/bin/java).
Selection Path Priority Status
------------------------------------------------------------
* 0 /usr/lib/jvm/java-14-openjdk-amd64/bin/java 1411 auto mode
1 /usr/lib/jvm/java-11-openjdk-amd64/bin/java 1111 manual mode
2 /usr/lib/jvm/java-14-openjdk-amd64/bin/java 1411 manual mode
3 /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java 1081 manual mode
Press <enter> to keep the current choice[*], or type selection number: 2
复制代码或者设置默认的 Java 版本：
/mnt/c/Users/vincent update-alternatives --config javac
There are 2 choices for the alternative javac (providing /usr/bin/javac).
Selection Path Priority Status
------------------------------------------------------------
* 0 /usr/lib/jvm/java-14-openjdk-amd64/bin/javac 1411 auto mode
1 /usr/lib/jvm/java-14-openjdk-amd64/bin/javac 1411 manual mode
2 /usr/lib/jvm/java-8-openjdk-amd64/bin/javac 1081 manual mode
Press <enter> to keep the current choice[*], or type selection number: 0
复制代码