[arch-general] How to have multiple JDKs parallel?

[Carsten Mattner]

I have a related question. I tried arch's openjdk packages and those
were successful in displaying Swing UIs.

Then, to check out newer JDKs and IBM's OpenJ9, I grabbed a
build from https://adoptopenjdk.net, and I just couldn't get
any Swing UI to display. It reported many exceptions and that
was it. Tried with different window managers and compositors.

Any idea what's different on Arch or where the adoptopenjdk builds
work?