There is a link Current and CurrentVersion which matches up the current Java environment with the appropriate version. JAVA_HOME is at /Library/Java/Home, but this is a link into a directory /System/Frameworks/JavaJVM.Framework/Versions which is used to switch between versions easily.
It is possible to run Java 1.4 on MacOS X Jaguar but it may interfere with operation of the standard environment. MacOS X 10.5 ( Snow Leopard) comes with Java 1.6. MacOS X 10.5 ( Leopard) comes with Java 1.5.
MacOS X 10.4 ( Tiger) comes with Java 1.4.2 installed, but Java 1.5 can be downloaded. MacOS X 10.2 ( Jaguar) comes with Java 1.3 MacOS X 10.3 ( Panther) comes with Java 1.4. Java is installed by default on every MacOS X installation. I hope these notes are of use to someone out there. These notes are the result of several weeks playing with different things and asking a LOT of questions on several mailing lists. For an updated guide for installing Tomcat 5/6 on Mac OS X 10.6 using MacPorts check
