BlockingQueue分析

1public interface BlockingQueue<E> extends Queue<E>
2
3boolean offer(E e);
4boolean add(E e);
5
6
7When using a capacity-restricted queue, this method is generally preferable to {@link #add}, which can fail to insert an element only by throwing an exception.

当使用大小限制的queue的时候，offer要优于add。

上述方法是extends from Queue。在BlockingQueue接口中添加了方法：

1/**
2     * Inserts the specified element into this queue, waiting if necessary
3     * for space to become available.
4     *
5     * @param e the element to add
6     * @throws InterruptedException if interrupted while waiting
7     * @throws ClassCastException if the class of the specified element
8     *         prevents it from being added to this queue
9     * @throws NullPointerException if the specified element is null
10     * @throws IllegalArgumentException if some property of the specified
11     *         element prevents it from being added to this queue
12     */
13    void put(E e) throws InterruptedException;
14
15    /**
16     * Inserts the specified element into this queue, waiting up to the
17     * specified wait time if necessary for space to become available.
18     *
19     * @param e the element to add
20     * @param timeout how long to wait before giving up, in units of
21     *        <tt>unit</tt>
22     * @param unit a <tt>TimeUnit</tt> determining how to interpret the
23     *        <tt>timeout</tt> parameter
24     * @return <tt>true</tt> if successful, or <tt>false</tt> if
25     *         the specified waiting time elapses before space is available
26     * @throws InterruptedException if interrupted while waiting
27     * @throws ClassCastException if the class of the specified element
28     *         prevents it from being added to this queue
29     * @throws NullPointerException if the specified element is null
30     * @throws IllegalArgumentException if some property of the specified
31     *         element prevents it from being added to this queue
32     */
33    boolean offer(E e, long timeout, TimeUnit unit)
34        throws InterruptedException;

增加了等待加入队列机制。put会一直等待，而offer则会灵活一些，等待一段时间。

-------------------取数据

queue中：

1/**
2     * Retrieves and removes the head of this queue.  This method differs
3     * from {@link #poll poll} only in that it throws an exception if this
4     * queue is empty.
5     *
6     * @return the head of this queue
7     * @throws NoSuchElementException if this queue is empty
8     */
9    E remove();
10
11    /**
12     * Retrieves and removes the head of this queue,
13     * or returns <tt>null</tt> if this queue is empty.
14     *
15     * @return the head of this queue, or <tt>null</tt> if this queue is empty
16     */
17    E poll();
18
19    /**
20     * Retrieves, but does not remove, the head of this queue.  This method
21     * differs from {@link #peek peek} only in that it throws an exception
22     * if this queue is empty.
23     *
24     * @return the head of this queue
25     * @throws NoSuchElementException if this queue is empty
26     */
27    E element();
28
29    /**
30     * Retrieves, but does not remove, the head of this queue,
31     * or returns <tt>null</tt> if this queue is empty.
32     *
33     * @return the head of this queue, or <tt>null</tt> if this queue is empty
34     */
35    E peek();

remove,element在queue为空时会throw exception，poll,peek不会。都是取head的数据。

BlockingQueue中：

1/**
2     * Retrieves and removes the head of this queue, waiting if necessary
3     * until an element becomes available.
4     *
5     * @return the head of this queue
6     * @throws InterruptedException if interrupted while waiting
7     */
8    E take() throws InterruptedException;
9
10    /**
11     * Retrieves and removes the head of this queue, waiting up to the
12     * specified wait time if necessary for an element to become available.
13     *
14     * @param timeout how long to wait before giving up, in units of
15     *        <tt>unit</tt>
16     * @param unit a <tt>TimeUnit</tt> determining how to interpret the
17     *        <tt>timeout</tt> parameter
18     * @return the head of this queue, or <tt>null</tt> if the
19     *         specified waiting time elapses before an element is available
20     * @throws InterruptedException if interrupted while waiting
21     */
22    E poll(long timeout, TimeUnit unit)
23        throws InterruptedException;

会有一个等待的过程，和加数据匹配。

int remainingCapacity();

返回理论上队列中还能存的对象个数。