Iterator implementation using composition that allows you to peek at the next value.

PeekIterator.java

public class PeekIterator<T> {
	@NonNull private final Iterator<T> iterator;
	@Nullable private final T current;

	public PeekIterator(Iterator<T> iter) {
		this.iterator = iter;
	}

	public boolean hasNext() {
		if (current != null) {
			return true;
		}
		return this.iterator.hasNext();
	}

	public T next() {
		if (current != null) {
			final T curr = current;
			current = null;
			return curr;
		}
		return this.iterator.next();
	}

	public T peek() {
		if (current == null) {
			current = this.next();
		}
		return current;
	}
}