So when should you use boxed primitives? They have several legitimate uses. The first is as elements, keys, and values in collections. You can’t put primitives in collections, so you’re forced to use boxed primitives. This is a special case of a more general one. You must use boxed primitives as type parameters in parameterized types and methods (Chapter 5), because the language does not permit you to use primitives. For example, you cannot declare a variable to be of type ThreadLocal<int>, so you must use ThreadLocal<Integer> instead. Finally, you must use boxed primitives when making
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Historically I think a lot of people used them to represent the absence of a value since you can't have a null int
