Java中的 ConcurrentLinkedQueue poll() 方法

ConcurrentLinkedQueue的poll()方法用于移除并返回这个 ConcurrentLinkedQueue 的头部。如果 ConcurrentLinkedQueue 为空，则此方法将返回 null。

句法：

public E poll()

返回：此方法移除并返回此 ConcurrentLinkedQueue 的头部，如果此队列为空，则返回null 。

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

示例 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
            queue = new ConcurrentLinkedQueue();
  
        // 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]

示例 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
            queue = new ConcurrentLinkedQueue();
  
        // 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： https: Java/util/concurrent/ConcurrentLinkedQueue.html#poll–