Using Linux Mint 18.2 sonya GettingStartedOnLinux.html UBUNTU lists: openjdk-7-jdk as one package. Where is it available? Google suggests: openjdk-7-jdk has no installation candidate
You can search for openjdk packages by writing: apt-cache search openjdk On my machine (Ubuntu 16.04 LTS) this search shows that these jdk packages are available: openjdk-7-jdk openjdk-8-jdk openjdk-9-jdk You can install e.g. the 8-jdk package (the one I have installed) by writing: sudo apt install openjdk-8-jdk