Why does char to int casting works and not char to Integer in Java

Question

I was working on a problem when I encountered this.

(int)input.charAt(i) //works
(Integer)input.charAt(i) // Does not work
// input being a string

The first thought I have is primitives are treated differently and that is why this is not working. But then I find it difficult to understand why would they have a Integer Wrapper class in the first place.

Edit: What are the advantages of having wrapper classes then? Is it just for not having a primitives presence and being more OO in design? I'm finding it difficult to understand how are tehy helpful. New doubt altogetehr.

Answer 1

You're right that primitives are treated differently. The following would work:

(Integer)(int)input.charAt(i);

The difference is that when the argument is an int, (Integer) boxes the integer. It's not actually a cast even though it looks like it. But if the argument is a char, then it would be a cast attempt; but primitives can't be cast to objects and therefore it doesn't work. What you can do is to first cast the char to int - this cast is okay since both are primitive types - and then the int can be boxed.

Of course, char -> Integer boxing could have been made working. "Why not?" is a good question. Probably there would have been little use for such feature, especially when the same function can be achieved by being a little bit more explicit. (Should char -> Long work too, then? And char -> Short? chars are 16-bit, so this would be most straightforward.)

Answer to edit: the advantage of wrapper classes is that wrapped primitives can be treated like objects: stored in a List<Integer>, for example. List<int> would not work, because int is not an object. So maybe even more relevant question would be, what are primitive non-objects doing in an OO language? The answer is in performance: primitives are faster and take less memory. The use case determines whether the convenience of objects or the performance of primitives is more important.