BlockingQueue阻塞队列的使用

1. BlockingQueue是阻塞队列。它是一个接口，主要的实现类有

2. add方法，队列添加满时抛出异常

   public class BlockingQueueTest {
       public static void main(String[] args) {
           test1();
       }
       
       //抛出异常的方法
       public static void test1(){
           BlockingQueue blockingQueue = new ArrayBlockingQueue(3);
           System.out.println(blockingQueue.add(1));
           System.out.println(blockingQueue.add(2));
           System.out.println(blockingQueue.add(3));
   
           System.out.println(blockingQueue.add(4));   //抛出异常
       }
   }
   

   添加第4个时 抛出异常

3. remove方法，队列为空时，继续移除元素抛出异常

   public class BlockingQueueTest {
       public static void main(String[] args) {
           test1();
       }
       
       //抛出异常的方法
       public static void test1(){
           BlockingQueue blockingQueue = new ArrayBlockingQueue(3);
           System.out.println(blockingQueue.add(1));
           System.out.println(blockingQueue.add(2));
           System.out.println(blockingQueue.add(3));
   
           System.out.println("=====================================");
   
           System.out.println(blockingQueue.remove());
           System.out.println(blockingQueue.remove());
           System.out.println(blockingQueue.remove());
   
           System.out.println(blockingQueue.remove());    //抛出异常
   
       }
   }
   

   上面只添加了3个元素，下面移除4个元素。当移除第4个元素时，抛出异常

   

4. offer和poll方法，有返回值，不抛出异常

   public class BlockingQueueTest {
       public static void main(String[] args) {
           test2();
       }
       
       //有返回值 不抛出异常
       public static void test2(){
           BlockingQueue blockingQueue = new ArrayBlockingQueue(3);
           System.out.println(blockingQueue.offer(1));
           System.out.println(blockingQueue.offer(2));
           System.out.println(blockingQueue.offer(3));
           System.out.println(blockingQueue.offer(4));         //不抛出异常 返回false
   
           System.out.println("=====================================");
   
           System.out.println(blockingQueue.poll());
           System.out.println(blockingQueue.poll());
           System.out.println(blockingQueue.poll());
   
           System.out.println(blockingQueue.poll());           //不抛出异常   返回null
   
       }
   }
   

   执行结果

   

5. 返回队首元素

   blockingQueue.element();	//返回队首元素 如果队列为null 抛出异常
   blockingQueue.peek()		//返回队首元素 如果队列为null 则返回null 不抛出异常
   

6. put方法，队列满时阻塞，直到队列有空位为止

   public class BlockingQueueTest {
       public static void main(String[] args) throws InterruptedException {
           test3();
       }
       public static void test3() throws InterruptedException {
           BlockingQueue blockingQueue = new ArrayBlockingQueue(3);
           blockingQueue.put(1);
           blockingQueue.put(2);
           blockingQueue.put(3);
           blockingQueue.put(4);       //程序在这里阻塞住
       }
   }
   

7. task方法，队列为空时阻塞，直到队列有元素为止

   public class BlockingQueueTest {
       public static void main(String[] args) throws InterruptedException {
           test3();
       }
       public static void test3() throws InterruptedException {
           BlockingQueue blockingQueue = new ArrayBlockingQueue(3);
           blockingQueue.put(1);
           blockingQueue.put(2);
           blockingQueue.put(3);
          // blockingQueue.put(4);       //程序在这里阻塞住
   
           System.out.println("======================");
   
           System.out.println(blockingQueue.take());
           System.out.println(blockingQueue.take());
           System.out.println(blockingQueue.take());
           System.out.println(blockingQueue.take());     //程序在这里阻塞住
       }
   }
   

8. 超时等待

   public class BlockingQueueTest {
       public static void main(String[] args) throws InterruptedException {
           test4();
       }
       public static void test4() throws InterruptedException {
           BlockingQueue blockingQueue = new ArrayBlockingQueue(3);
           System.out.println(blockingQueue.offer(1));
           System.out.println(blockingQueue.offer(2));
           System.out.println(blockingQueue.offer(3));
           System.out.println(blockingQueue.offer(4, 2, TimeUnit.SECONDS));   //等待2秒 如果加入成功返回true,否则返回false
   
           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2秒 如果有值可以取就返回值，否则返回null
       }
   }
   
   

9. 总结上面4组API

   方法	抛出异常	不抛异常，返回值	阻塞	超时阻塞
   添加	add	offer	put	offer(obj,v,t)
   移除	remove	poll	task	poll(v,t)
   查看队首	element	peek	—	—