SCJP: can't widen and then box, but you can box and then widen

Question

I\'m studying for the SCJP exam and I ran into an issue I can\'t really wrap my head around.

The book says you can\'t widen and then box, but you can box and then wi

Answer 1

Basically what this means is that widening only works with primitive types, not the wrappers. If you box first, you get a wrapper (byte -> Byte). But the wrappers - Byte, Double, Float, Integer, Long and Short do not have any inheritance relationship (IS-A). A Long parameter can't accept a Byte for instance.

So you must widen first (byte -> long) and then box (long -> Long).