All of the differences are WAY too numerous to list here. However,
The official Java web site contains all the documentation
documentation you need about Java. For example,
here is the index for docs about Java 1.4. If you scroll down the page, you can find
Enhancements and Changes in Java 2 SDK v1.4.2 and
New Features since J2SE 1.3 Platform. Each release of Java has similar documentation. You will probably have to search the archives to find information about versions older than 1.3. However, it is available, so don't give up.
Layne