安装JDK

在命令行中输入

javac

得到反馈：

Command 'javac' not found, but can be installed with:

sudo apt install openjdk-11-jdk-headless  # version 11.0.8+10-0ubuntu1~20.04, or
sudo apt install default-jdk              # version 2:1.11-72
sudo apt install openjdk-13-jdk-headless  # version 13.0.3+3-1ubuntu2
sudo apt install openjdk-14-jdk-headless  # version 14.0.1+7-1ubuntu1
sudo apt install openjdk-8-jdk-headless   # version 8u265-b01-0ubuntu2~20.04
sudo apt install ecj                      # version 3.16.0-1

我选择的是

sudo apt install openjdk-11-jdk-headless

配置VSCode

用VSCode打开一个java文件，弹窗拓展都下载。Done。