Java BlockingDeque poll()方法及示例

BlockingDeque 的 poll() 方法返回Deque容器中的前端元素，并将其删除。如果容器是空的，它返回 null 。

语法

public E poll()

参数： 该方法不接受任何参数。

返回： 如果Deque容器不是空的，该方法返回该容器的前部元素，并将其删除。如果容器是空的，它返回null。

注意 ： BlockingDeque 的poll()方法已经从Java中的LinkedBlockingDeque类中继承了。

以下程序说明了BlockingDeque的poll()方法。

程序1 :

// 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<Integer> BD
            = new LinkedBlockingDeque<Integer>();
  
        // 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]

程序2 :

// 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<Integer> BD
            = new LinkedBlockingDeque<Integer>();
  
        // 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://docs.oracle.com/javase/7/docs/api/java/util/concurrent/BlockingDeque.html#poll(long, %20java.util.concurrent.TimeUnit)。