Queue/Deque接口

Queue

• 先入先出（FIFO）的数据结构

boolean add(E element)
boolean offer(E element)
在队列尾部添加元素，如果队列已满，add将抛出IllegalStateException，offer返回false

public boolean add(E e) {
        if (offer(e))
            return true;
        else
            throw new IllegalStateException("Queue full");
    }

E remove()
E poll()
删除并返回队头元素，如果队空，remove抛出NoSuchElementException， poll返回null

public E remove() {
        E x = poll();
        if (x != null)
            return x;
        else
            throw new NoSuchElementException();
    }

E element()
E peek()
返回队头元素，如果队空，element抛出NoSuchElementException， peek返回null

public E element() {
        E x = peek();
        if (x != null)
            return x;
        else
            throw new NoSuchElementException();
    }

上面三段代码来自jdk1.8 java.util.AbstractQueue

Deque

• 双端队列，只能在队列的首尾进行操作
• 实现类：ArrayDeque, ConcurrentLinkedDeque, LinkedBlockingDeque, LinkedList
• Deque被推荐用来取代Stack类

Summary of Deque methods

||First Element (Head)||Last Element (Tail)||
|-|
||Throws exception|Special value|Throws exception|Special value|
|Insert|addFirst(e)|offerFirst(e)|addLast(e)|offerLast(e)|
|Remove|removeFirst()|pollFirst()|removeLast()|pollLast()|
|Examine|getFirst()|peekFirst()|getLast()|peekLast()|