Java中的 BlockingDeque poll() 方法及示例

BlockingDeque的poll()方法返回 Deque 容器中的最前面的元素并将其删除。如果容器为空，则返回null 。

句法：

public E poll()

参数：此方法不接受任何参数。

返回：如果容器不为空，则此方法返回 Deque 容器的前元素并将其删除。如果容器为空，则返回null 。

注意： BlockingDeque的 poll() 方法继承自Java中的 LinkedBlockingDeque 类。

下面的程序说明了 BlockingDeque 的 poll() 方法：

方案一：

// Java Program Demonstrate poll()
// method of BlockingDeque
  
import java.util.concurrent.LinkedBlockingDeque;
import java.util.concurrent.BlockingDeque import java.util.*;
  
public class GFG {
    public static void main(String[] args)
  
    {
  
        // create object of BlockingDeque
        BlockingDeque BD
            = new LinkedBlockingDeque();
  
        // Add numbers to end of BlockingDeque
        BD.add(7855642);
        BD.add(35658786);
        BD.add(5278367);
        BD.add(74381793);
  
        // Print the queue
        System.out.println("Blocking Deque: " + BD);
  
        System.out.println("Front element in Deque: " + BD.poll());
  
        // One element is deleted as poll was called
        System.out.println("Blocking Deque: " + BD);
    }
}

输出：

Blocking Deque: [7855642, 35658786, 5278367, 74381793]
Front element in Deque: 7855642
Blocking Deque: [35658786, 5278367, 74381793]

方案二：

// Java Program Demonstrate poll()
// method of BlockingDeque
// when Deque is empty
  
import java.util.concurrent.LinkedBlockingDeque;
import java.util.concurrent.BlockingDeque import java.util.*;
  
public class GFG {
    public static void main(String[] args)
  
    {
  
        // create object of BlockingDeque
        BlockingDeque BD
            = new LinkedBlockingDeque();
  
        // Add numbers to end of BlockingDeque
        BD.add(7855642);
        BD.add(35658786);
        BD.add(5278367);
        BD.add(74381793);
  
        // Print the queue
        System.out.println("Blocking Deque: " + BD);
  
        // empty deque
        BD.clear();
  
        System.out.println("Front element in Deque: " + BD.poll());
    }
}

输出：

Blocking Deque: [7855642, 35658786, 5278367, 74381793]
Front element in Deque: null

参考： https: Java/util/concurrent/BlockingDeque.html#poll(long, %20java.util.concurrent.TimeUnit)