In the JRuby release notes, I often find a particular version of JRuby is compatible with which version of Ruby. How about which version of Java runtime it is compatible with?
For example, http://jruby.org/2016/05/27/jruby-9-1-2-0 page mentions it is compatible with Ruby 2.x but says nothing about Java runtime version.
its not in the release notes as its not changing between point releases (unless specified), should be around download but isn't. currently, you can find out in the project README
each major version of JRuby supports the JVM supported around the time its released, later point releases usually fix support for newer Java versions but do not drop support for older ones ... thus :
JRuby 1.7.x supports Java 6 or later (7, 8, might support 9)
JRuby 9.0/1 supports Java 7 or later (8, will support Java 9)
JRuby 9.2/3 only support Java 8 or later