Better stack traces
ClassCastException didn't used to have a message but I noticed that now it has a message that includes the cast class and the object class. That extra info is very beneficial. (Note that only recently could I start using 1.5 in my main product so I am behind the times a bit.)
What other common Throwables need improved messages?
NullPointerException should have the name of the variable. I entered an RFE for this:
I created another RFE to be able to add extra info to stack traces.