Java ConcurrentLinkedQueue poll()方法

ConcurrentLinkedQueue 的 poll() 方法用于移除并返回该ConcurrentLinkedQueue的头部。如果ConcurrentLinkedQueue是空的，那么这个方法将返回null。

语法

public E poll()

返回： 该方法删除并返回该ConcurrentLinkedQueue的头部，如果该队列为空，则返回空。

下面的程序说明了ConcurrentLinkedQueue的poll()方法。

例1 :

// Java Program Demonstrate poll()
// method of ConcurrentLinkedQueue
  
import java.util.concurrent.*;
  
public class GFG {
    public static void main(String[] args)
    {
  
        // create an ConcurrentLinkedQueue
        ConcurrentLinkedQueue<Integer>
            queue = new ConcurrentLinkedQueue<Integer>();
  
        // Add Numbers to queue
        queue.add(4353);
        queue.add(7824);
        queue.add(78249);
        queue.add(8724);
  
        // Displaying the existing ConcurrentLinkedQueue
        System.out.println("ConcurrentLinkedQueue: " + queue);
  
        // apply poll()
        int response1 = queue.poll();
  
        // print after applying poll method
        System.out.println("Head: " + response1);
  
        // Displaying the existing ConcurrentLinkedQueue
        System.out.println("Current ConcurrentLinkedQueue: " + queue);
    }
}

输出。

ConcurrentLinkedQueue: [4353, 7824, 78249, 8724]
Head: 4353
Current ConcurrentLinkedQueue: [7824, 78249, 8724]

例2 :

// Java Program Demonstrate poll()
// method of ConcurrentLinkedQueue
  
import java.util.concurrent.*;
  
public class GFG {
    public static void main(String[] args)
    {
  
        // create an ConcurrentLinkedQueue
        ConcurrentLinkedQueue<String>
            queue = new ConcurrentLinkedQueue<String>();
  
        // Add String to queue
        queue.add("Aman");
        queue.add("Amar");
        queue.add("Sanjeet");
        queue.add("Rabi");
  
        // Displaying the existing ConcurrentLinkedQueue
        System.out.println("ConcurrentLinkedQueue: " + queue);
  
        // apply poll() on queue
        String response1 = queue.poll();
  
        // print after applying poll method
        System.out.println("Head: " + response1);
  
        // Displaying the existing ConcurrentLinkedQueue
        System.out.println("Current ConcurrentLinkedQueue: " + queue);
  
        // apply poll() on queue more than one time
        queue.poll();
        queue.poll();
  
        // Displaying the existing ConcurrentLinkedQueue
        System.out.println("After 2 poll() applied\n"
                           + "ConcurrentLinkedQueue: " + queue);
    }
}

输出。

ConcurrentLinkedQueue: [Aman, Amar, Sanjeet, Rabi]
Head: Aman
Current ConcurrentLinkedQueue: [Amar, Sanjeet, Rabi]
After 2 poll() applied
ConcurrentLinkedQueue: [Rabi]

参考资料: https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ConcurrentLinkedQueue.html#poll-