Java中的BlockingDeque pollFirst()方法及其示例

BlockingDeque 的 pollFirst() 方法会返回Deque容器中的第一个元素，并将其删除。如果容器为空，则返回 null 。

语法:

public E pollFirst()

参数: 该方法不接受任何参数。

返回值: 如果容器不为空，则此方法返回Deque容器中的第一个元素并将其删除。如果容器为空，则返回null。

Note : Java中的 BlockingDeque 的pollFirst()方法已从LinkedBlockingDeque类继承而来。

下面的程序示例说明了 BlockingDeque 的pollFirst()方法:

Program 1:

//Java程序演示BlockingDeque的pollFirst()方法

import java.util.concurrent.LinkedBlockingDeque;
import java.util.concurrent.BlockingDeque;
import java.util.*;

public class GFG {
    public static void main(String[] args)

    {

        // 创建BlockingDeque对象
        BlockingDeque BD
            = new LinkedBlockingDeque();

        // 在BlockingDeque的末尾添加数字
        BD.addFirst(7855642);
        BD.addFirst(35658786);
        BD.addFirst(5278367);
        BD.addFirst(74381793);

        // 打印队列
        System.out.println("Blocking Deque: " + BD);

        // 打印并删除
        System.out.println("Front element in Deque: " + BD.pollFirst());

        // 删除前一个元素后的BlockingDeque
        System.out.println("Blocking Deque: " + BD);
    }
}

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

Program 2:

//Java程序演示BlockingDeque的pollFirst()方法
//当Deque为空时

import java.util.concurrent.LinkedBlockingDeque;
import java.util.concurrent.BlockingDeque;
import java.util.*;

public class GFG {
    public static void main(String[] args)

    {

        // 创建LinkedBlockingDeque对象
        LinkedBlockingDeque BD
            = new LinkedBlockingDeque();

        // 在BlockingDeque的末尾添加数字
        BD.add(7855642);
        BD.add(35658786);
        BD.add(5278367);
        BD.add(74381793);

        // 打印队列
        System.out.println("Blocking Deque: " + BD);

        //清空
        BD.clear();

        System.out.println("Front element in Deque: " + BD.pollFirst());
    }
}

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

Reference: https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/BlockingDeque.html#pollFirst(long,%20java.util.concurrent.TimeUnit)