BlockingQueue 常用API

複習看下錶即可

Level.	放入		取出
1	add	隊列滿？異常：return true	remove	隊列空？異常：return head
2	offer	隊列滿？return false：return true	poll	隊列空？return null：return head
3	put	隊列滿？阻塞：return [void]	take	隊列空？阻塞：return head

add、offer、put

BlockingQueue 的put、offer、add區別，看註釋：

BlockingQueue<Object> taskQueue = new LinkedBlockingQueue<Object>(queueSize);
taskQueue.put(task);    // 隊列滿？阻塞:return void
taskQueue.offer(task);  // 隊列滿？return false:return true
taskQueue.add(task);    // 隊列滿? 報異常：return true;

測試程序：

public static void main(String[] args) {
   int queueSize = 2;
    BlockingQueue<Object> taskQueue1 = new LinkedBlockingQueue<Object>(queueSize);
    BlockingQueue<Object> taskQueue2 = new LinkedBlockingQueue<Object>(queueSize);
    BlockingQueue<Object> taskQueue3 = new LinkedBlockingQueue<Object>(queueSize);

    for (int i = 0; i < queueSize + 1; i++) {
        System.out.println("================for " + (i + 1));
        Object o = new Object();
        try {
            System.out.println("add:" + taskQueue1.add(o));
        } catch (Exception e) {
            e.printStackTrace();
        }
        System.out.println("offer:" + taskQueue2.offer(o));
        try {
            System.out.println("taskQueue3 size:" + taskQueue3.size());
            taskQueue3.put(o);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

輸出：

================for 1
add:true
offer:true
befor put ,taskQueue3 size:0
after put ,taskQueue3 size:1
================for 2
add:true
offer:true
befor put ,taskQueue3 size:1
after put ,taskQueue3 size:2
================for 3
java.lang.IllegalStateException: Queue full
	at java.util.AbstractQueue.add(AbstractQueue.java:98)
	at com.yh.stu.concurrent.dp.threadpool.dmjuc.DMThreadPool.main(DMThreadPool.java:47)
offer:false
befor put ,taskQueue3 size:2

輸出最後一行缺少了after put ,taskQueue3 size:3, 因爲taskQueue3 滿了，taskQueue3.put(o) 阻塞等待

2、remove、poll、take

看註釋：

taskQueue3.remove();	// 隊列空？異常:return head;
taskQueue3.poll();  	// 隊列空？return null:return head;
taskQueue3.take(); 		// 隊列空？阻塞:return head;

測試程序：

public static void main(String[] args) {
    int queueSize = 2;
    BlockingQueue<Object> taskQueue1 = new LinkedBlockingQueue<Object>(queueSize);
    BlockingQueue<Object> taskQueue2 = new LinkedBlockingQueue<Object>(queueSize);
    BlockingQueue<Object> taskQueue3 = new LinkedBlockingQueue<Object>(queueSize);
    new Thread(new Runnable() {
        @Override
        public void run() {
            ThreadUtils.sleep(1000);
            try {
                taskQueue3.take(); // 隊列空？阻塞:return head;
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }).start();
    for (int i = 0; i < queueSize + 1; i++) {
        System.out.println("================for " + (i + 1));
        Object o = new Object();
        try {
            System.out.println("add:" + taskQueue1.add(o));
        } catch (Exception e) {
            e.printStackTrace();
        }
        System.out.println("offer:" + taskQueue2.offer(o));
        try {
            System.out.println("befor put ,taskQueue3 size:" + taskQueue3.size());
            taskQueue3.put(o);
            System.out.println("after put ,taskQueue3 size:" + taskQueue3.size());
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

3、總結

Level.	放入		取出
1	add	隊列滿？異常：return true	remove	隊列空？異常：return head
2	offer	隊列滿？return false：return true	poll	隊列空？return null：return head
3	put	隊列滿？阻塞：return [void]	take	隊列空？阻塞：return head