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    Java中的java.util.PriorityQueue.poll()方法用于检索或获取和删除队列的第一个元素或队列头部的元素。peek()方法只检索的元件在头部但poll() 也与检索移除element。如果队列为空,则返回NULL。

    句法:

    Priority_Queue.poll()

    参数:该方法不接受任何参数。

    返回值:该方法返回队列头部的元素,如果队列为空,则返回NULL。

    下面的程序说明了java.util.PriorityQueue.poll()方法的使用

    程序1:

    // Java code to illustrate poll()
    import java.util.*;
    
    public class PriorityQueueDemo {
        public static void main(String args[])
        {
            // Creating an empty PriorityQueue
            PriorityQueue<String> queue = new PriorityQueue<String>();
    
            // Use add() method to add elements into the Queue
            queue.add("Welcome");
            queue.add("To");
            queue.add("Geeks");
            queue.add("For");
            queue.add("Geeks");
    
            // Displaying the PriorityQueue
            System.out.println("Initial PriorityQueue: " + queue);
    
            // Fetching and removing the element at the head of the queue
            System.out.println("The element at the head of the"
                               + " queue is: " + queue.poll());
    
            // Displaying the Queue after the Operation
            System.out.println("Final PriorityQueue: " + queue);
        }
    }
    

    输出:

    Initial PriorityQueue: [For, Geeks, To, Welcome, Geeks]
    The element at the head of the queue is: For
    Final PriorityQueue: [Geeks, Geeks, To, Welcome]

    程序2:

    // Java code to illustrate poll()
    import java.util.*;
    
    public class PriorityQueueDemo {
        public static void main(String args[])
        {
            // Creating an empty PriorityQueue
            PriorityQueue<Integer> queue = new PriorityQueue<Integer>();
    
            // Use add() method to add elements into the Queue
            queue.add(10);
            queue.add(15);
            queue.add(30);
            queue.add(20);
            queue.add(5);
    
            // Displaying the PriorityQueue
            System.out.println("Initial PriorityQueue: " + queue);
    
            // Fetching the element at the head of the queue
            System.out.println("The element at the head of the"
                               + " queue is: " + queue.poll());
    
            // Displaying the Queue after the Operation
            System.out.println("Final PriorityQueue: " + queue);
        }
    }
    

    输出:

    Initial PriorityQueue: [5, 10, 30, 20, 15]
    The element at the head of the queue is: 5
    Final PriorityQueue: [10, 15, 30, 20]

     
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