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
posted @ 2020-09-14 11:47  不停的奋斗  阅读(132)  评论(0)  编辑  收藏  举报