Unable to locate package

问题描述：

ubuntu系统安装文件时报错

apt-get install openjdk-11-jdk
E: Unable to locate package openjdk-11-jdk

解决办法：

apt-get install software-properties-common
apt-get update
add-apt-repository ppa:openjdk-r/ppa
apt-get install openjdk-11-jdk

参考文献：

1. Package 'openjdk-11-jdk' has no installation candidate

2. Fix ‘add-apt-repository command not found’ Error on Ubuntu and Debian