Using Linux Mint 18.2 sonya
as one package. Where is it available?
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:
You can install e.g. the 8-jdk package (the one I have installed) by writing:
sudo apt install openjdk-8-jdk