5、阻塞队列（BlockingQueue）和同步队列（Synch

队列：FIFO（先进先出）
阻塞：

• 写入：如果队列满了，就必须阻塞等待

• 读取：如果队列为空，必须阻塞等待生产。

  
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ArrayBlockingQueue的四种API

示例1：（会抛出异常）

 /**
  *会抛出异常
  */
 public static void test1(){
        ArrayBlockingQueue blockingQueue = new ArrayBlockingQueue<>(3);

        System.out.println(blockingQueue.add("a"));
        System.out.println(blockingQueue.add("b"));
        System.out.println(blockingQueue.add("c"));
        //System.out.println(blockingQueue.add("d"));  //报异常：IllegalStateException: Queue full

        System.out.println(blockingQueue.element());  //查看队首元素

        System.out.println("============================");

        System.out.println(blockingQueue.remove());
        System.out.println(blockingQueue.remove());
        System.out.println(blockingQueue.remove());
        //System.out.println(blockingQueue.remove());  //报异常：NoSuchElementException
    }

示例2：（有返回值，不会抛出异常）

 public static void test2(){
        //队列大小
        ArrayBlockingQueue blockingQueue = new ArrayBlockingQueue<>(3);

        System.out.println(blockingQueue.offer("a"));
        System.out.println(blockingQueue.offer("b"));
        System.out.println(blockingQueue.offer("c"));
        System.out.println(blockingQueue.offer("d")); //false   不抛出异常

        System.out.println(blockingQueue.peek()); //查看队首元素

        System.out.println("============================");

        System.out.println(blockingQueue.poll());
        System.out.println(blockingQueue.poll());
        System.out.println(blockingQueue.poll());
        System.out.println(blockingQueue.poll());  //null
    }

返回值：

true
true
true
false
============================
a
b
c
null

示例3：等待，阻塞（一直阻塞）

 public static void test3() throws InterruptedException {
        //队列大小
        ArrayBlockingQueue blockingQueue = new ArrayBlockingQueue<>(3);

        blockingQueue.put("a");
        blockingQueue.put("b");
        blockingQueue.put("c");
        //blockingQueue.put("d"); //队列没有位置了，会一直阻塞

        System.out.println(blockingQueue.take());
        System.out.println(blockingQueue.take());
        System.out.println(blockingQueue.take());
        System.out.println(blockingQueue.take());  //没有元素了，也会一直等待（阻塞）

    }

示例3：等待，阻塞（等待超时）

public static void test4() throws InterruptedException {
        //队列大小
        ArrayBlockingQueue blockingQueue = new ArrayBlockingQueue<>(3);

        System.out.println(blockingQueue.offer("a"));
        System.out.println(blockingQueue.offer("b"));
        System.out.println(blockingQueue.offer("c"));
        System.out.println(blockingQueue.offer("d",2, TimeUnit.SECONDS));  //等待超过2秒钟就退出

        System.out.println("==============================");

        System.out.println(blockingQueue.poll());
        System.out.println(blockingQueue.poll());
        System.out.println(blockingQueue.poll());
        System.out.println(blockingQueue.poll(2,TimeUnit.SECONDS));//等待超过2秒钟就退出
    }

SynchronousQueue 同步队列

没有容量，进去一个元素必须等待取出来后才能往里面放一个元素。（put、take）

package com.company.blockingqueue;

import java.util.concurrent.BlockingDeque;
import java.util.concurrent.SynchronousQueue;
import java.util.concurrent.TimeUnit;

/**
 *同步队列
 */
public class TestSynchronizedQueue {

    public static void main(String[] args) {
        SynchronousQueue<String> synchronousQueue = new SynchronousQueue<>();

        new Thread(()->{
            try {
                System.out.println(Thread.currentThread().getName()+" put 1");
                synchronousQueue.put("1");
                System.out.println(Thread.currentThread().getName()+" put 2");
                synchronousQueue.put("2");
                System.out.println(Thread.currentThread().getName()+" put 3");
                synchronousQueue.put("3");
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        },"T1").start();

        new Thread(()->{
            try {
                TimeUnit.SECONDS.sleep(3);
                System.out.println(Thread.currentThread().getName()+" take "+synchronousQueue.take());
                TimeUnit.SECONDS.sleep(3);
                System.out.println(Thread.currentThread().getName()+" take "+synchronousQueue.take());
                TimeUnit.SECONDS.sleep(3);
                System.out.println(Thread.currentThread().getName()+" take "+synchronousQueue.take());
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        },"T2").start();
    }

}

结果：

T1 put 1
T2 take 1
T1 put 2
T2 take 2
T1 put 3
T2 take 3