I updated to Java 5, and that gave the Java Preferences app. According to the Apple tech notes, that app only came with the Java 5 update on Tiger.
You can open a terminal and run java -version to find out which java version you are running
That will only tell me which version I am using, it will not change it. There are some very >>limited<< options in Java Prefs to change the version
applets use, but you cannot guarantee that apps will use a certain version. There are other options however; Google "change Java version mac" and get a plethora of (sometimes passionate) debate on the matter.
The simplest is to change the default JDK by changing the symlink in /System/Library/Frameworks/JavaVM.framework/Versions to point to the version you want (this is where the passion comes in)
eg:
cd /System/Library/Frameworks/JavaVM.framework/Versions
sudo ln -fhsv <directory_of_version_I_want_to_be_default> CurrentJDK
here is a nice little shell script that will do that for you (along with a lot of passionate debate following):
http://hints.macworld.com/article.php?story=20060121171126988
If you want to do it the "Apple" way, here are two good helps, and the reasons why changing the symlink may not be a good idea (which are worth considering):
http://developer.apple.com/library/mac/#releasenotes/Java/Java50Release3RN/UsingJ2SE50/UsingJava5.html#//apple_ref/doc/uid/TP40003184-CH5-SW1
http://hintsforums.macworld.com/showthread.php?t=47531
(this one also gives a good primer on Java versioning on a Mac. Well laid out, IMO)
Thanks
updated 2011-02-09