20220210 java.util.concurrent.BlockingQueue 方法说明

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方法对比

方法声明

// 添加元素方法
boolean add(E e);
boolean offer(E e);
boolean offer(E e, long timeout, TimeUnit unit) throws InterruptedException;
void put(E e) throws InterruptedException;


// 移除元素方法
boolean remove(Object o);
E remove();
E poll();
E poll(long timeout, TimeUnit unit) throws InterruptedException;
E take() throws InterruptedException;


// 检查元素方法
E element();
E peek();

• 注意方法的参数、返回值和抛出异常
• remove 方法有两个重载方法，一个有入参，返回 boolean ；另一个没有入参，返回队列里的元素
• 方法声明上有抛出 InterruptedException 异常的方法，意思不是指超时后抛出此异常，而是指接收到中断信号后抛出此异常

代码示例

public class BlockingQueueDemo {

    private static BlockingQueue<String> blockingQueue = new ArrayBlockingQueue<>(3);

    public static void main(String[] args) {

        // add、offer、put
        // testAdd();
        // testOffer();
        // testPut();

        // remove、poll、take
        // testRemove();
        // testRemoveNoArg();
        // testPoll();
        // testTake();

        // element、peek
        // testElement();
        // testPeek();

        // 测试中断异常
        testInterruptedException();


        System.out.println(blockingQueue);
    }

    private static void testInterruptedException() {
        Thread thread = new Thread(() -> {
            try {
                blockingQueue.put("a");
                System.out.println("添加成功 a");
                blockingQueue.put("b");
                System.out.println("添加成功 b");
                blockingQueue.put("c");
                System.out.println("添加成功 c");
                blockingQueue.put("d");
                System.out.println("添加成功 d");
            } catch (InterruptedException e) {
                System.out.println("抛出异常");
                System.err.println(e);  // java.lang.InterruptedException
                e.printStackTrace();    // java.lang.InterruptedException
            }
        });
        thread.start();

        try {
            TimeUnit.SECONDS.sleep(5);
            thread.interrupt();
            System.out.println("线程中断");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    private static void testElement() {
        System.out.println(blockingQueue.element());    // a    // 阻塞队列为空时，抛出异常 java.util.NoSuchElementException
        System.out.println(blockingQueue.element());    // a
        System.out.println(blockingQueue.element());    // a
    }

    private static void testPeek() {
        System.out.println(blockingQueue.peek());    // a    // 阻塞队列为空时，返回 null
        System.out.println(blockingQueue.peek());    // a
        System.out.println(blockingQueue.peek());    // a
    }

    private static void testRemove() {
        blockingQueue.remove("a");
        blockingQueue.remove("b");
        System.out.println(blockingQueue.remove("c")); // true
        System.out.println(blockingQueue.remove("d")); // false
    }

    private static void testRemoveNoArg() {
        System.out.println(blockingQueue.remove()); // a
        System.out.println(blockingQueue.remove()); // b
        System.out.println(blockingQueue.remove()); // c
        System.out.println(blockingQueue.remove()); // java.util.NoSuchElementException
    }

    private static void testPoll() {
        System.out.println(blockingQueue.poll());   // a
        System.out.println(blockingQueue.poll());   // b
        System.out.println(blockingQueue.poll()); // c

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

        try {
            System.out.println(blockingQueue.poll(5, TimeUnit.SECONDS)); // null    // 阻塞5s
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    private static void testTake() {
        try {
            System.out.println(blockingQueue.take());
            System.out.println(blockingQueue.take());
            System.out.println(blockingQueue.take());
            System.out.println(blockingQueue.take());   // 线程阻塞
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    private static void testAdd() {
        blockingQueue.add("a");
        blockingQueue.add("b");
        System.out.println(blockingQueue.add("c")); // true
        // System.out.println(blockingQueue.add("d")); // java.lang.IllegalStateException: Queue full
    }

    private static void testOffer() {
        blockingQueue.offer("a");
        blockingQueue.offer("b");
        System.out.println(blockingQueue.offer("c")); // true

        System.out.println(blockingQueue.offer("d")); // false

        try {
            System.out.println(blockingQueue.offer("e", 5, TimeUnit.SECONDS)); // false     // 阻塞5s
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    private static void testPut() {
        try {
            blockingQueue.put("a");
            System.out.println("插入完成 a");
            blockingQueue.put("b");
            System.out.println("插入完成 b");
            blockingQueue.put("c");
            System.out.println("插入完成 c");
            blockingQueue.put("d");     // 线程阻塞
            System.out.println("插入完成 d");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

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