阻塞队列

一、阻塞队列说明

ArrayBlockingQueue是个底层以数组实现为基础的阻塞队列，由于该阻塞队列的构造函数中都有capacity，所以它是一个有界阻塞队列。

 常用方法和区别如下：

	抛出异常	特殊值	阻塞
插入	// 放入元素，如果队列满了，则抛出异常 public boolean add(E e) { return super.add(e); } public boolean add(E e) { if (offer(e)) return true; else throw new IllegalStateException("Queue full"); } 真正调用的是父类AbstractQueue.add(E e)方法	public boolean offer(E e) { 　　checkNotNull(e); final ReentrantLock lock = this.lock; lock.lock(); try { if (count == items.length) return false; else { enqueue(e); return true; } } finally { lock.unlock(); } } 如果队列满了，返回false	public void put(E e) throws InterruptedException { checkNotNull(e); final ReentrantLock lock = this.lock; lock.lockInterruptibly(); try { while (count == items.length) notFull.await(); enqueue(e); } finally { lock.unlock(); } } 如果队列满了，则阻塞等待
移除	public E remove() { E x = poll(); if (x != null) return x; else throw new NoSuchElementException(); } 如果队列为空，则抛NoSuchElementException();	public E poll() { final ReentrantLock lock = this.lock; lock.lock(); try { return (count == 0) ? null : dequeue(); } finally { lock.unlock(); } } 如果队列为空，返回null	public E take() throws InterruptedException { final ReentrantLock lock = this.lock; lock.lockInterruptibly(); try { while (count == 0) notEmpty.await(); return dequeue(); } finally { lock.unlock(); } } 如果队列为空，则阻塞等待
读取	public E element() { E x = peek(); if (x != null) return x; else throw new NoSuchElementException(); } 如果对列为空，则抛NoSuchElementException();	public E peek() { final ReentrantLock lock = this.lock; lock.lock(); try { return itemAt(takeIndex); // null when queue is empty } finally { lock.unlock(); } } 队列为空，返回null	不可用
	上述3个方法在AbstractQueue中	上述3个方法在ArrayBlockingQueue中	底层使用了Condition队列