int[] and Integer[] arrays – What is the difference?

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There is a difference at run-time.

int[] is an array of primitive int values. Integer[] is an “object” array, holding references to Integer objects.

Most important practical difference: int[] cannot hold null values.

But I’m still confused: does int[] store just a primitive values? If so – doesn’t it mean that primitive types can live on heap without being wrapped?

int[] does store primitive types. And the array itself lives on the heap. However, those primitives are allocated as part of the array. They are not stored separately elsewhere on the heap. This is very similar to how a primitive field is part of an object instance: The object is on the heap, and its field is an integral part of that object (whereas for a non-primitive field, only the reference is stored inside the object and the target instance that reference points at is stored separately on the heap).

You could say the int is “wrapped” inside the array.

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