JUC:阻塞队列

第一组api(add,remove,element)
add(E) 在尾部添加元素,如果队列满了,抛出IllegalStateException: Queue full异常
remove() 删除队列的头元素,如果队列为空,抛出 NoSuchElementException 异常
element() 查看队列的头元素,如果队列为空,抛出 NoSuchElementException 异常(底层调用的是peek())

        blockingQueue.add("a");
        blockingQueue.add("b");
        blockingQueue.add("c");
//         超过容量会抛异常 java.lang.IllegalStateException: Queue full
//        blockingQueue.add("d");
        System.out.println(blockingQueue.remove());
        System.out.println(blockingQueue.remove());
        System.out.println(blockingQueue.remove());
//        空队列继续取元素 抛出没有元素异常  java.util.NoSuchElementException
//        System.out.println(blockingQueue.remove());
//        element() 查看队列的头元素,但不删除(空队列会抛出NoSuchElementException)
        System.out.println(blockingQueue.element());

第二组api(offer,poll,peek)
offer(E) 在尾部添加元素,队列已满,返回false
poll() 从头部弹出一个元素,空队列返回null
peek() 查看队列的头元素,空队列返回null

        System.out.println(blockingQueue.offer("a"));
        System.out.println(blockingQueue.offer("b"));
        System.out.println(blockingQueue.offer("c"));
//        System.out.println(blockingQueue.offer(null)); // NullPointerException
        System.out.println(blockingQueue.offer("d")); // 队列已满,不抛异常,返回值为 false

        System.out.println(blockingQueue.poll());
        System.out.println(blockingQueue.poll());
        System.out.println(blockingQueue.poll());
        System.out.println(blockingQueue.poll()); // 空队列,继续弹出元素 无异常,返回值为 null

        System.out.println(blockingQueue.peek()); // 获取队列的头元素,空队列返回 null

第三组api(offer(E,time,TimeUnit),poll(time,timeUnit))
offer("a", 2, TimeUnit.SECONDS) 队列已满,等待2秒,时间过了直接放弃插入
poll(2, TimeUnit.SECONDS) 队列已空,等待两秒,如果还未空,直接返回null

try {
            System.out.println(blockingQueue.offer("a", 2, TimeUnit.SECONDS));
            System.out.println(blockingQueue.offer("b", 2, TimeUnit.SECONDS));
            System.out.println(blockingQueue.offer("c", 2, TimeUnit.SECONDS));
//            队列已满,等待2秒种,仍未加入队列,放弃添加并返回false
            System.out.println(blockingQueue.offer("d", 2, TimeUnit.SECONDS));
            System.out.println(blockingQueue.poll(2, TimeUnit.SECONDS));
            System.out.println(blockingQueue.poll(2, TimeUnit.SECONDS));
            System.out.println(blockingQueue.poll(2, TimeUnit.SECONDS));
//          队列已空,等待两秒,仍然为空,放弃取出元素,返回null
            System.out.println(blockingQueue.poll(2, TimeUnit.SECONDS));

        } catch (InterruptedException e) {
            e.printStackTrace();
        }

第四组api(put(),take() )
put() 如果队列已满,会一直阻塞,直到队列有空位置,再插入队列
take() 如果队列已空,会一直阻塞,直到队列有新元素,再取出元素

        try {
            blockingQueue.put("a");
            blockingQueue.put("b");
            blockingQueue.put("c");
            // 如果队列已满,会一直阻塞,直到队列有空位置,再插入队列
            blockingQueue.put("d");
            System.out.println(blockingQueue.take());
            System.out.println(blockingQueue.take());
            System.out.println(blockingQueue.take());
            // 如果队列已空,会一直阻塞,直到队列有新元素,取出元素
            System.out.println(blockingQueue.take());
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

同步队列: SynchronousQueue

每一个put操作，就需要有一个 take操作！

BlockingQueue<String> blockingQueue = new SynchronousQueue<>();
        // A 存
        new Thread(() -> {
            try {
                System.out.println(Thread.currentThread().getName() + " put a");
                blockingQueue.put("a");
                System.out.println(Thread.currentThread().getName() + " put b");
                blockingQueue.put("b");
                System.out.println(Thread.currentThread().getName() + " put c");
                blockingQueue.put("c");
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }, "A").start();

        // B 取
        new Thread(() -> {
            try {
                TimeUnit.SECONDS.sleep(2);
                System.out.println(Thread.currentThread().getName() + " get "+ blockingQueue.take());

                TimeUnit.SECONDS.sleep(2);
                System.out.println(Thread.currentThread().getName() + " get "+ blockingQueue.take());

                TimeUnit.SECONDS.sleep(2);
                System.out.println(Thread.currentThread().getName() + " get "+ blockingQueue.take());
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }, "B").start();

结果: