How do I make a choose SDK dropdown?

I want to be able to use this dropdown in my own plugin:

I am writing my own project setup using the wizard steps etc. I am using Swing and IntelliJ's built in form editor.

I want them to be able to select the SDK, like you can on a regular Java project. I have seen another plugin use this exact button so I know there must be a way.

These forums are quiet, so please if you have even a hint of what to do or how to put me on the right track, please kindly offer it.

Many thanks