ExtendableIterator.java

import java.util.Deque;
import java.util.Iterator;
import java.util.ArrayDeque;

public class ExtendableIterator<T> implements Iterator<T> {
	
	public Deque<Iterator<T>> its = new ArrayDeque<Iterator<T>>();

	public ExtendableIterator() {
	
	}

	public ExtendableIterator(Iterator<T> it) {
		this();
		this.extend(it);
	}
	
	@Override
	public boolean hasNext() {
		// this is true since we never hold empty iterators
		return !its.isEmpty() && its.peekLast().hasNext();
	}
	
	@Override
	public T next() {
		T next = its.peekFirst().next();
		if (!its.peekFirst().hasNext()) {
			its.removeFirst();
		}
		return next;
	}
	
	public void extend(Iterator<T> it) {
		if (it.hasNext()) {
			its.addLast(it);
		}
	}
}