Queue接口源码解析

队列

先进先出

入队列：offer

出队列：poll

队头元素：peek

继承：Collection抽象类

源码如下：

package java.util;

public interface Queue<E> extends Collection<E> {
    /**
     * 队列插入元素
     *
     * @param e the element to add
     * @return <tt>true</tt> (as specified by {@link Collection#add})
     * @throws IllegalStateException if the element cannot be added at this
     *         time due to capacity restrictions
     * @throws ClassCastException if the class of the specified element
     *         prevents it from being added to this queue
     * @throws NullPointerException if the specified element is null and
     *         this queue does not permit null elements
     * @throws IllegalArgumentException if some property of this element
     *         prevents it from being added to this queue
     */
    boolean add(E e);

    /**
     * 队列插入元素
     * 插入失败，抛出异常
     * @param e the element to add
     * @return <tt>true</tt> if the element was added to this queue, else
     *         <tt>false</tt>
     * @throws ClassCastException if the class of the specified element
     *         prevents it from being added to this queue
     * @throws NullPointerException if the specified element is null and
     *         this queue does not permit null elements
     * @throws IllegalArgumentException if some property of this element
     *         prevents it from being added to this queue
     */
    boolean offer(E e);

    /**
     * 获取队顶元素，并删除该元素
     * 空的时候，抛出异常
     * @return the head of this queue
     * @throws NoSuchElementException if this queue is empty
     */
    E remove();

    /**
     * 获取队顶元素，并删除该元素
     * 空的时候，返回null
     * @return the head of this queue, or <tt>null</tt> if this queue is empty
     */
    E poll();

    /**
     * 查看队顶元素，但是不删除该元素、
     * 空的时候，抛出异常
     * @return the head of this queue
     * @throws NoSuchElementException if this queue is empty
     */
    E element();

    /**
     * 查看队顶元素，但是不删除该元素、
     * 空的时候，返回 null
     *
     * @return the head of this queue, or <tt>null</tt> if this queue is empty
     */
    E peek();
}