I think I'm going to try and post to the blog info on MRJ on Mac OS Classic. MRJ is Macintosh Runtime for Java. I'm trying to find out how far back you can target a Java app, and what processor/OS versions are required. So let the spam begin.

MRJ 2.2.5

The latest version of
MRJ is Gold Certified by Oracle, and includes numerous enhancements.
Everyone with an earlier version of MRJ 2.2.x is encouraged to update
to MRJ 2.2.5.

System requirements:
PowerPC-based Apple Macintosh computer
Mac OS 8.1 or later
Minimum 40 MB of RAM.

MRJ 2.2.4

The latest version of MRJ includes an important fix to MRJ 2.2.3. Anyone who has installed MRJ 2.2.3 or is using Mac OS 9.1 is strongly urged to upgrade to MRJ 2.2.4.

System requirements:
PowerPC-based Apple Macintosh computer
Mac OS 8.1 or later
Minimum 40 MB of RAM.

MRJ 2.1.2 requires a PowerPC-based Apple Macintosh computer, Mac OS
7.6.1 or later, and at least 32 MB of RAM. QuickTime 3.0 also improves performance.

MRJ 1.0.2 works on computers with 68030 or 68040 microprocessors or PowerPC microprocessors. You also need System 7.5 or later, a minimum of 8 MB of RAM (16 MB is strongly recommended) and at least 7 MB of free disk space. Computers with 68030 or 68040 microprocessors must have 32-bit addressing turned on. This can be done by using the Memory control panel.