java - 这个基于优先级队列的通用框架有什么错误？我找不到

Question

谁能帮我找出输入错误的部分？这里有哪些问题区域？

class Queue<E> {
 /**
 * A First in, First Out Queue ADT
 */
 public List<E> elements = new ArrayList<E>();
 public void enqueue(E element) {}
 public E dequeue(E element) {}
 public int size() {}
 public boolean isEmpty() {}
}
class PriorityQueue<E extends Comparable<E>> extends Queue<E> {
 /**
 * A Queue where each element has a priority
 * Higher priority elements are pushed to the front of the queue
 */
 @Override
 public Object dequeue(E element) {}
 public void enqueue(E element, int priority) {}
}