Java 中的队列轮询()方法

原文:https://www.geeksforgeeks.org/queue-poll-method-in-java/

队列接口 的 poll() 方法返回并移除容器前端的元素。它删除容器中的元素。当队列为空时，该方法不会抛出异常，而是返回 null 。

语法:

E poll()

返回:该方法返回容器前面或队列头部的元素。当队列为空时，它返回空值。

以下程序说明了队列的轮询()方法:

程序一:借助 链接列表 。

// Java Program Demonstrate poll()
// method of Queue

import java.util.*;

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

        // create object of Queue
        Queue<Integer> Q
            = new LinkedList<Integer>();

        // Add numbers to end of Queue
        Q.add(7855642);
        Q.add(35658786);
        Q.add(5278367);
        Q.add(74381793);

        // print queue
        System.out.println("Queue: " + Q);

        // print head and deletes the head
        System.out.println("Queue's head: " + Q.poll());

        // print head and deleted the head
        System.out.println("Queue's head: " + Q.poll());
    }
}

输出:

Queue: [7855642, 35658786, 5278367, 74381793]
Queue's head: 7855642
Queue's head: 35658786

程序 2: 演示队列变空时队列的轮询()方法

// Java Program Demonstrate poll()
// method of Queue when the Queue becomes empty

import java.util.*;

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

        // create object of Queue
        Queue<Integer> Q
            = new LinkedList<Integer>();

        // Add numbers to end of Queue
        Q.add(423);
        Q.add(3432);

        // print queue
        System.out.println("Queue: " + Q);

        // print head and deletes the head
        System.out.println("Queue's head: " + Q.poll());

        // print head and deleted the head
        System.out.println("Queue's head: " + Q.poll());

        // print queue
        System.out.println("Queue: " + Q);

        // print null as Queue is empty now
        System.out.println("Queue's head: " + Q.poll());
    }
}

输出:

Queue: [423, 3432]
Queue's head: 423
Queue's head: 3432
Queue: []
Queue's head: null

节目 3: 借助 ArrayDeque 。

// Java Program Demonstrate poll()
// method of Queue

import java.util.*;

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

        // create object of Queue
        Queue<Integer> Q
            = new ArrayDeque<Integer>();

        // Add numbers to end of Queue
        Q.add(7855642);
        Q.add(35658786);
        Q.add(5278367);
        Q.add(74381793);

        // print queue
        System.out.println("Queue: " + Q);

        // print head and deletes the head
        System.out.println("Queue's head: " + Q.poll());

        // print head and deleted the head
        System.out.println("Queue's head: " + Q.poll());
    }
}

输出:

Queue: [7855642, 35658786, 5278367, 74381793]
Queue's head: 7855642
Queue's head: 35658786

程序 4: 在的配合下。

// Java Program Demonstrate poll()
// method of Queue

import java.util.*;
import java.util.concurrent.ConcurrentLinkedDeque;

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

        // create object of Queue
        Queue<Integer> Q
            = new ConcurrentLinkedDeque<Integer>();

        // Add numbers to end of Queue
        Q.add(7855642);
        Q.add(35658786);
        Q.add(5278367);
        Q.add(74381793);

        // print queue
        System.out.println("Queue: " + Q);

        // print head and deletes the head
        System.out.println("Queue's head: " + Q.poll());

        // print head and deleted the head
        System.out.println("Queue's head: " + Q.poll());
    }
}

输出:

Queue: [7855642, 35658786, 5278367, 74381793]
Queue's head: 7855642
Queue's head: 35658786

项目 5: 在的帮助下，链接锁定了。

// Java Program Demonstrate poll()
// method of Queue

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

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

        // create object of Queue
        Queue<Integer> Q
            = new LinkedBlockingDeque<Integer>();

        // Add numbers to end of Queue
        Q.add(7855642);
        Q.add(35658786);
        Q.add(5278367);
        Q.add(74381793);

        // print queue
        System.out.println("Queue: " + Q);

        // print head and deletes the head
        System.out.println("Queue's head: " + Q.poll());

        // print head and deleted the head
        System.out.println("Queue's head: " + Q.poll());
    }
}

输出:

Queue: [7855642, 35658786, 5278367, 74381793]
Queue's head: 7855642
Queue's head: 35658786

参考:https://docs . Oracle . com/javase/8/docs/API/Java/util/queue . html # poll–

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