Question

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Why can Integer and int be used interchangably?

I am trying to understand the difference between these. Can I declare something to be an int for example and then compare this with a number that I put in an Integer? Also why does Java have the two. Why not just combine these?

Can someone help me by showing me a 3-4 line code example of how each is used?

Answer 1

int primitive is not an object. Arrays allow primiteves:

int[] array = new int[10];

but generics don’t:

List<int>  //won't compile

This is the primary reason to use wrapper classes these days. Also you can use Integer where Object is expected. Finally Integer can have null value if you want to implement optionality.

Note that there are some languages that dealt with that inconsistency. In c# you have value types, in scala Int class extend from AnyVal class while normal objects extend AnyRef (both of these extend from Any).