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PriorityQueue poll() Method in Java

  • Difficulty Level : Hard
  • Last Updated : 10 Dec, 2018

The java.util.PriorityQueue.poll() method in Java is used to retrieve or fetch and remove the first element of the Queue or the element present at the head of the Queue. The peek() method only retrieved the element at the head but the poll() also removes the element along with the retrieval. It returns NULL if the queue is empty.

Syntax:

Priority_Queue.poll()

Parameters: The method does not take any parameters.

Return Value: The method returns the element at the head of the Queue else returns NULL if the Queue is empty.

Below programs illustrate the use of java.util.PriorityQueue.poll() method:
Program 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);
    }
}
Output:
Initial PriorityQueue: [For, Geeks, To, Welcome, Geeks]
The element at the head of the queue is: For
Final PriorityQueue: [Geeks, Geeks, To, Welcome]

Program 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);
    }
}
Output:
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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