BlockingQueue的add/offer/put,remove/poll/take, element/peek比较

当前源码以ArrayBlockingQueue为例子

add/offer/put的区别：

1、 add: 和collection的add一样，当队列满时，调用add()方法抛出异常IllegalStateException异常
2、 调用off()方法当队列满时返回的 false。
3、调用put方法时候，当当前队列等于设置的最大长度时，将阻塞，直到能够有空间插入元素

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

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();
        }
    }

   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();
       }
   }

remove/poll/take的区别

1、remove，remove()是从队列中删除第一个元素。remove() 的行为与 Collection 接口的相似
2、poll，但是新的 poll() 方法时有值时返回值，在空集合调用时不是抛出异常，只是返回 null,
3、take: 获取并移除此队列的头部，在元素变得可用之前一直等待 。queue的长度 == 0 的时候，一直阻塞

public void remove() {
            // assert lock.getHoldCount() == 0;
            final ReentrantLock lock = ArrayBlockingQueue.this.lock;
            lock.lock();
            try {
                if (!isDetached())
                    incorporateDequeues(); // might update lastRet or detach
                final int lastRet = this.lastRet;
                this.lastRet = NONE;
                if (lastRet >= 0) {
                    if (!isDetached())
                        removeAt(lastRet);
                    else {
                        final E lastItem = this.lastItem;
                        // assert lastItem != null;
                        this.lastItem = null;
                        if (itemAt(lastRet) == lastItem)
                            removeAt(lastRet);
                    }
                } else if (lastRet == NONE)
                    throw new IllegalStateException();
                // else lastRet == REMOVED and the last returned element was
                // previously asynchronously removed via an operation other
                // than this.remove(), so nothing to do.

                if (cursor < 0 && nextIndex < 0)
                    detach();
            } finally {
                lock.unlock();
                // assert lastRet == NONE;
                // assert lastItem == null;
            }
        }

public E poll() {
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            return (count == 0) ? null : dequeue();
        } finally {
            lock.unlock();
        }
    }

/**
     * Extracts element at current take position, advances, and signals.
     * Call only when holding lock.
     */
    private E dequeue() {
        // assert lock.getHoldCount() == 1;
        // assert items[takeIndex] != null;
        final Object[] items = this.items;
        @SuppressWarnings("unchecked")
        E x = (E) items[takeIndex];
        items[takeIndex] = null;
        if (++takeIndex == items.length)
            takeIndex = 0;
        count--;
        if (itrs != null)
            itrs.elementDequeued();
        notFull.signal();
        return x;
    }

public E take() throws InterruptedException {
        final ReentrantLock lock = this.lock;
        lock.lockInterruptibly();
        try {
            while (count == 0)
                notEmpty.await();
            return dequeue();
        } finally {
            lock.unlock();
        }
    }

peek，element区别：

检测操作，element() 和 peek() 用于在队列的头部查询元素。与 remove() 方法类似，在队列为空时， element() 抛出一个IllegalStateException异常，而 peek() 返回 null
Queue.java源码

/**
     * Retrieves, but does not remove, the head of this queue.  This method
     * differs from {@link #peek peek} 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 element();

ArrayBlockingQueue中源码

public E peek() {
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            return itemAt(takeIndex); // null when queue is empty
        } finally {
            lock.unlock();
        }
    }