Java中的 BlockingDeque pollFirst() 方法及示例

BlockingDeque的pollFirst()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 pollFirst()

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 容器中的前元素并删除该元素。如果容器为空，则返回null 。

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

下面的程序说明了 BlockingDeque 的 pollFirst() 方法：

方案一：

// Java Program Demonstrate pollFirst()
// 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.addFirst(7855642);
        BD.addFirst(35658786);
        BD.addFirst(5278367);
        BD.addFirst(74381793);
  
        // Print the queue
        System.out.println("Blocking Deque: " + BD);
  
        // prints and deletes
        System.out.println("Front element in Deque: " + BD.pollFirst());
  
        // Deque after deletion of front element
        System.out.println("Blocking Deque: " + BD);
    }
}

输出：

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

方案二：

// Java Program Demonstrate pollFirst()
// 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 LinkedBlockingDeque
        LinkedBlockingDeque 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.pollFirst());
    }
}

输出：

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

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