Maintaining backward compatibility

[Muhammed Syyid]

Whats the best way for maintaining backward compatibility with legacy
applets. I'm working on a legacy applet (JDK 1.18) and was wondering
what common practices are used to maintain compatibility (besides
updating the client plugin ). I was thinking of maintaining two
separate codebases. The newer full featured one being jdk1.4.x
compatible and the older legacy one for clients that are unable to
upgrade. Can I programmatically (javascript) determine browser jdk
versions and load the appropriate applet and/or just instantiate
different classes from within the applet. Any pointers to the right
resources would be greatly appreciated Thanks

Muhammed