How can I find my Java version in Big Sur?

I am successfully running a Java application in Big Sur. I was using it prior to Big Sur and -- after upgrading to Big Sur -- it works fine. I have had none of the Java issues some others have described in these forums.

A friend is trying to run the same application, he asked me what version of Java he should use.

However, I cannot find Java in the preferences panel, and when I type Java in the Terminal window, I get a message that it's not installed and a link to Oracle.

The app's download page says "Vassal 3.4.11 requires Java 11 or later. The Mac OS X disk image and the Windows installer come with the version of Java Vassal will use."

I am running that app successfully -- so I know Java is on my machine somewhere.

Isn't it?