Distinction between the capacity of an array list and the size of an array

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If you allocate a new array with arr = new Employee[100], the size of that array (arr.length) is going to be 100. It has 100 elements. All the elements are initially null (as this is an array of object references), but still, there are 100 elements.

If you do something like list = new ArrayList <Employee>(100), and try to check list.size(), you’ll get 0. There are no elements in the list.

Internally, it’s true that the ArrayList allocates enough place to put 100 items before it needs to extend its capacity, but that’s an internal implementation detail, and the list presents its content to you as “no items stored”. Only if you actually do list.add(something), you’ll have items in the list.

So although the list allocates storage in advance, the API with which it communicates with the program tells you there are no items in it. The null items in its internal array are not available to you – you cannot retrieve them or change them.

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