- Queue 中 remove() 和 poll() 都是用來從隊列頭部刪除一個元素。
- 在隊列元素為空的情況下，remove() 方法會拋出NoSuchElementException異常，poll() 方法只會返回 null 。
JDK1.8 中的源碼解釋
/**
* Retrieves and removes the head of this queue. This method differs
* from {@link #poll poll} only in that it throws an exception if this
* queue is empty.
*
* @return the head of this queue
* @throws NoSuchElementException if this queue is empty
*/
E remove();
/**
* Retrieves and removes the head of this queue,
* or returns {@code null} if this queue is empty.
*
* @return the head of this queue, or {@code null} if this queue is empty
*/
E poll();