Method enqueue

java/Chapter 3/Question3_7/AnimalQueue.java:10–18

(Animal a)

	private int order = 0;
	
	public void enqueue(Animal a) {
		a.setOrder(order);
		order++;
		if (a instanceof Dog) {
			dogs.addLast((Dog) a);
		} else if (a instanceof Cat) {
			cats.addLast((Cat)a);
		}
	}
	
	public Animal dequeueAny() {
		if (dogs.size() == 0) {