There is a talk called "Java for Small Coding Tasks" by the author of Core Java: https://www.youtube.com/watch?v=04wFgshWMdA

Apparently, this is the way to do it:

    ///usr/bin/env java --source 25 "$0" "$@" ; exit $?

I don't do Java. As one comment on the video said, 'This presentation is the epitome of the old saying: "When your only tool is a hammer, every problem looks like a nail"'