JRuby had supported duck-typing of java.lang.Throwable hierarchy, to act like Ruby's Exception, for a long time.

There's java.lang.Throwable#backtrace which maps the Java stack-trace into an Array.

The backtrace_locations method are a later Ruby language feature and so wasn't considered for addiiton.
It would be desired to support backtrace_location with JRuby's Java integration as well, esp. since frameworks such as Rails might do rescue Exception (which catched Java throwables) and assume backtrace_locations exists.