Collection Iterator

// Collection is an interface
public interface Collection<E> {
    boolean add(E element);
    Iterator<E> iterator();
    ...  
}

public interface Iterator<E> {
    E next();
    boolean hasNext();
    void remove();
}

public class MergeIterator {
	Iterator<Integer> left;
	Iterator<Integer> right;
	int lastLeft;
	int lastRight;
	boolean leftNotUsed;
	
	public MergeIterator (Iterator<Integer> left, Iterator<Integer> right) {
		this.left = left;
		this.right = right;
		if (left.hasNext()) {
			lastLeft = left.next();
			leftNotUsed = true;
		} else if (right.hasNext()) {
			lastRight = right.next();
			leftNotUsed = false;
		} 
	}
	
	public boolean hasNext() {
		return left.hasNext() | right.hasNext();
	}
	
	public int next() throws Exception {
		if (!left.hasNext() && !right.hasNext()) {
			throw new Exception(" ");
		}
		if (left.hasNext() && !right.hasNext()) {
			if (leftNotUsed) {
				leftNotUsed = false;
				return lastLeft;
			}
			return left.next();
		}
		
		if (!left.hasNext() && right.hasNext()) {
			if (leftNotUsed) {
				leftNotUsed = false;
				return lastLeft;
			}
			return right.next();
		}
		
		if (leftNotUsed) {
			lastRight = right.next();
			if (lastLeft < lastRight) {
				leftNotUsed = false;
				return lastLeft;
			} else {
				return lastRight;
			}
		} else {
			lastLeft = left.next();
			if (lastRight < lastLeft) {
				leftNotUsed = true;
				return lastRight;
			} else {
				leftNotUsed = false;
				return lastLeft;
			}
		}
	}
}