我制作了一個 QueueRunner 課程。我試圖找出在 poll() 或 Offer() 之后迭代到隊列的頭部，以使用 peek() 返回隊列的頭部。不過，我在返回隊列的頭部或前面時遇到了麻煩。Public class Queue<T> {private ArrayList<T> elements;public Queue() {    this.elements = new ArrayList<T>();}/*** Offers an element to the end of the queue.** @param    T   item*/public void offer(T element) {    this.elements.add(element);}/*** Peeks at, but does not remove, the element at the head of the queue.** @return   T*/public T peek() {    if(this.elements.size()==0) {        return null;    }    else {        return this.elements;    // return this.elements.get(this.elements.size()-1);    }}/*** Polls an element from the head of the queue.** @return   T*/public T poll() {    return this.elements.remove(0);}