Design an iterator that supports the `peek` operation on an existing iterator in addition to the `hasNext` and the `next` operations.

Implement the `PeekingIterator` class:

- `PeekingIterator(Iterator<int> nums)` Initializes the object with the given integer iterator `iterator`.
- `int next()` Returns the next element in the array and moves the pointer to the next element.
- `boolean hasNext()` Returns `true` if there are still elements in the array.
- `int peek()` Returns the next element in the array without moving the pointer.

Note: Each language may have a different implementation of the constructor and `Iterator`, but they all support the `int next()` and `boolean hasNext()` functions.

Example 1:

    Input
    ["PeekingIterator", "next", "peek", "next", "next", "hasNext"]
    [[[1, 2, 3]], [], [], [], [], []]
    Output
    [null, 1, 2, 2, 3, false]

    Explanation
    PeekingIterator peekingIterator = new PeekingIterator([1, 2, 3]); // [1,2,3]
    peekingIterator.next();    // return 1, the pointer moves to the next element [1,2,3].
    peekingIterator.peek();    // return 2, the pointer does not move [1,2,3].
    peekingIterator.next();    // return 2, the pointer moves to the next element [1,2,3]
    peekingIterator.next();    // return 3, the pointer moves to the next element [1,2,3]
    peekingIterator.hasNext(); // return False

Constraints:

- `1 <= nums.length <= 1000`
- `1 <= nums[i] <= 1000`
- All the calls to `next` and `peek` are valid.
- At most `1000` calls will be made to `next`, `hasNext`, and `peek`.

Follow up: How would you extend your design to be generic and work with all types, not just integer?