Every Java Object has the methods wait() and notify() (and additional variants). I have never used these and I suspect many others haven't. Why are these so fundamental that every object has to have them and is there a performance hit in having them (presumably some state is stored in them)?
EDIT to emphasize the question. If I have a List<Double> with 100,000 elements then every Double has these methods as it is extended from Object. But it seems unlikely that all of these have to know about the threads that manage the List.
EDIT excellent and useful answers. @Jon has a very good blog post which crystallised my gut feelings. I also agree completely with @Bob_Cross that you should show a performance problem before worrying about it. (Also as the nth law of successful languages if it had been a performance hit then Sun or someone would have fixed it).