You will need to have Japanese Language support installed. For Earlier MacOS systems (before MacOS 9?), you will need to install either "KanjiTalk"(MacOS J), or the Japanese Language Kit (JLK). Both of which will run you over $100? An alternative on MacOS 7.5 or later might be to try UniText, but I have had no reports confirming or denying this. May as well just upgrade to the latest MacOS.
MacOS 8.5 or later should have it on the installation CDs. You must choose a "Custom Install", rather than an "Easy Install" to get the Japanese support. You should be able to do a Custom Install even after you have MacOS installed on your computer.
Once you have Japanese support installed,
before running a java prog that needs to display Japanese, go to
and move Japanese to the top for menus and dialogs.
Once you have made these adjustments, you should be able to just double-click on any properly made jar file (eg: my jdrill2.jar file) and have it start up like a regular program, properly displaying Kanji.