Apple's Developer technote here:
Explains what are all the Mac OS X releases for Java, and how to determine if you have the that version. If you don't check http://www.apple.com/swupdates/ to see if you can run that update on your machine.
Note: Java releases should not be confused with versions of Java released on Microsoft platforms which require ActiveX as a plugin. These versions have hit and miss compatibility with the Mac under Mac OS X, and are sometimes more compatible with Netscape 4 or Internet Explorer 5 for Mac OS 9, while other times only work under emulation or virtualization engines for running Windows on the Mac.