[LeetCode] Problem 284 - Peeking Iterator

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Given an Iterator class interface with methods: next() and hasNext(), design and implement a PeekingIterator that support the peek() operation – it essentially peek() at the element that will be returned by the next call to next().

Example

Assume that the iterator is initialized to the beginning of the list: [1,2,3].

Call next() gets you 1, the first element in the list.
Now you call peek() and it returns 2, the next element. Calling next() after that still return 2.
You call next() the final time and it returns 3, the last element.
Calling hasNext() after that should return false.

Follow up

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

Code

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private Iterator<Integer> iterator;
private Integer next;

public PeekingIterator(Iterator<Integer> iterator) {
    this.iterator = iterator;
    next = iterator.next();
}

public Integer peek() {
    return next;
}

@Override
public Integer next() {
    int result = next;
    next = iterator.hasNext() ? iterator.next() : null;
    return result;
}

@Override
public boolean hasNext() {
    return next != null;
}