Autoboxing is rather scary. While I fully understand the difference between == and .equals I can't but help have the follow bug the hell out of me:

    final List<Integer> foo = Arrays.asList(1, 1000);
    final List<Integer> bar = Arrays.asList(1, 1000);
    System.out.println(foo.get(0) == bar.get(0));
    System.out.println(foo.get(1) == bar.get(1));

That prints

true
false

Why did they do it this way? It something to do with cached Integers, but if that is the case why don't they just cache all Integers used by the program? Or why doesn't the JVM always auto unbox to primitive?

Printing false false or true true would have been way better.

EDIT

I disagree about breakage of old code. By having foo.get(0) == bar.get(0) return true you already broke the code.

Can't this be solved at the compiler level by replacing Integer with int in byte code (as long as it is never assigned null)