public interface BlockingQueue
extends Queue
阻塞队列支持在检索元素时如果队列为空发生阻塞，直到有可以操作的元素。同时在插入元素如果没有多余的容量支持，就阻塞，直到有可用空间
BlockingQueue方法有四种形式，根据处理操作的方式不同，有的能立即得到结果，有的会在某个时间点获得结果：一种方法抛出异常，另一种方法返回特殊值（根据操作的不同，可以为null或false），第三个在操作成功之前无限期阻塞当前线程，第四个在放弃之前仅阻塞给定的最大时间限制。下表总结了这些方法：
不能插入null，如果插入null实现类会报空指针异常
阻塞队列可能有容量限制，否则容量就是Integer.MAX_VALUE
BlockingQueue的实现主要用于生产者-消费者队列，但还支持收集接口。BlockingQueue的实现是线程安全的。所有队列方法都使用内部锁或其他形式的并发控制原子性。
使用示例，基于典型的生产者-消费者场景。注意，BlockingQueue可以安全地用于多个生产者和多个消费者。
class Producer implements Runnable {
private final BlockingQueue queue;
Producer(BlockingQueue q) { queue = q; }
public void run() {
try {
while (true) { queue.put(produce()); }
} catch (InterruptedException ex) { ... handle ...}
}
Object produce() { ... }
}
class Consumer implements Runnable {
private final BlockingQueue queue;
Consumer(BlockingQueue q) { queue = q; }
public void run() {
try {
while (true) { consume(queue.take()); }
} catch (InterruptedException ex) { ... handle ...}
}
void consume(Object x) { ... }
}
class Setup {
void main() {
BlockingQueue q = new SomeQueueImplementation();
Producer p = new Producer(q);
Consumer c1 = new Consumer(q);
Consumer c2 = new Consumer(q);
new Thread(p).start();
new Thread(c1).start();
new Thread(c2).start();
}
}
阻塞队列满足happens——before即程序中的查询操作发生在从另一个线程中对BlockingQueue访问或删除该元素操作之前。
重要方法
/**
* 如果可以在不违反容量限制的情况下立即将指定元素插入此队列，
* 则成功时返回true，如果当前没有可用空间，则抛出IllegalStateException。
* 当使用容量受限队列时，通常最好使用offer
*
*
* @param e 一个要加入的元素
* @return 添加成功放回true
* @throws IllegalStateException在没有可用容量的时候
* @throws ClassCastException
* @throws NullPointerException
* @throws IllegalArgumentException if some property of the specified
* element prevents it from being added to this queue
*/
boolean add(E e);
/**
*如果可以在不违反容量限制的情况下立即将指定元素插入此队列，
*则成功时返回true，如果当前没有可用空间，则返回false。
*当使用容量受限队列时，此方法通常比add（E）更可取，后者只能通过抛出异常才能插入元素。
*
*@param e the element to add
* @return {@code true} if the element was added to this queue, else
* {@code false}
* @throws ClassCastException if the class of the specified element
* prevents it from being added to this queue
* @throws NullPointerException if the specified element is null
* @throws IllegalArgumentException if some property of the specified
* element prevents it from being added to this queue
*/
boolean offer(E e);
/**
* 将指定的元素插入此队列，必要时等待空间可用。会发生阻塞
*
*
* @param e the element to add
* @throws InterruptedException if interrupted while waiting
* @throws ClassCastException if the class of the specified element
* prevents it from being added to this queue
* @throws NullPointerException if the specified element is null
* @throws IllegalArgumentException if some property of the specified
* element prevents it from being added to this queue
*/
void put(E e) throws InterruptedException;
/**
* 将指定的元素插入此队列，如果没有空间空间，则等阻塞指定的时间。
*
* @param e the element to add
* @param timeout how long to wait before giving up, in units of
* {@code unit}
* @param unit a {@code TimeUnit} determining how to interpret the
* {@code timeout} parameter
* @return {@code true} if successful, or {@code false} if
* the specified waiting time elapses before space is available
* @throws InterruptedException 如果在等待时被打断抛出
* @throws ClassCastException if the class of the specified element
* prevents it from being added to this queue
* @throws NullPointerException if the specified element is null
* @throws IllegalArgumentException if some property of the specified
* element prevents it from being added to this queue
*/
boolean offer(E e, long timeout, TimeUnit unit)
throws InterruptedException;
/**
* 检索并删除此队列的头，如果队列为空就阻塞直到有新的元素加入。
*
* @return 返回头部元素
* @throws InterruptedException 如果在等待时被打断抛出
*/
E take() throws InterruptedException;
/**
* 检索并删除此队列的头，如果队列为空，等待指定的时间直到有可操作的元素。
*
* @param timeout how long to wait before giving up, in units of
* {@code unit}
* @param unit a {@code TimeUnit} determining how to interpret the
* {@code timeout} parameter
* @返回队列头部, or {@code null} if the
* specified waiting time elapses before an element is available
* @throws InterruptedException 如果在等待时被打断抛出
*/
E poll(long timeout, TimeUnit unit)
throws InterruptedException;
/**
*返回队列可插入元素的个数，最大为interge的最大值，建议不要用此方法判断插入元素是否成功，因为线程不安全
*
* @返回剩余容量
*/
int remainingCapacity();
/**
* 移除一个指定的元素
*成功返回true，失败返回false
*
*Throws:
*ClassCastException - if the class of the specified element is incompatible with this queue (optional)
*NullPointerException - if the specified element is null (optional)
*/
boolean remove(Object o);
/**
*判断指定元素是否在队列中
*
* @param o object to be checked for containment in this queue
* @return {@code true} if this queue contains the specified element
* @throws ClassCastException if the class of the specified element
* is incompatible with this queue
* (<a href="../Collection.html#optional-restrictions">optional</a>)
* @throws NullPointerException if the specified element is null
* (<a href="../Collection.html#optional-restrictions">optional</a>)
*/
public boolean contains(Object o);
/**
*移除所有元素并将元素添加到集合中
*
* @param c the collection to transfer elements into
* @return the number of elements transferred
* @throws UnsupportedOperationException if addition of elements
* is not supported by the specified collection
* @throws ClassCastException if the class of an element of this queue
* prevents it from being added to the specified collection
* @throws NullPointerException if the specified collection is null
* @throws IllegalArgumentException if the specified collection is this
* queue, or some property of an element of this queue prevents
* it from being added to the specified collection
*/
int drainTo(Collection<? super E> c);
/**
* 移除所有元素并将元素添加到指定大小的集合中
*
* @param c the collection to transfer elements into
* @param maxElements the maximum number of elements to transfer
* @return the number of elements transferred
* @throws UnsupportedOperationException if addition of elements
* is not supported by the specified collection
* @throws ClassCastException if the class of an element of this queue
* prevents it from being added to the specified collection
* @throws NullPointerException if the specified collection is null
* @throws IllegalArgumentException if the specified collection is this
* queue, or some property of an element of this queue prevents
* it from being added to the specified collection
*/
int drainTo(Collection<? super E> c, int maxElements);
``
