Why does java have an int and int Integer datatype and can I move data from one to another? [duplicate]

Question

Possible Duplicate:
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).

Answer 2

See boxing of types in Java. There is talk of making them exactly the same starting with Java 9.

Answer 3

• Primitive int type and Integer class are different types. You can't compare directly a primitive int with a Integer object. You need to get intValue from the Integer object.
• Yes, this is a required feature. Java and some other languages has these kinds of object wrappers for primitive types to handle the situations where an object is required. For example, a collection class will expect objects, you can't use primitive int with them. So you will need a Integer wrapper.