This class is an implementation of the List interface that keeps the references to the elements in an array. That way, this is fairly fast to access an element by index. On the other hand, inserting an element to ArrayList can be costly. It needs moving all references above the inserted element one index higher, and it may also require resizing the backing array in case there is no room in the original one to store the new element. Essentially, this means allocating a new array and copying all references to it.

The reallocation of the array may be optimized if we know how large the array will grow and call the ensureCapacity method. This will resize the array to the size provided as argument, even if the currently used slots are less numbered.