Queue poll() method in Java
Last Updated :
20 Oct, 2021
Improve
The poll() method of Queue Interface returns and removes the element at the front end of the container. It deletes the element in the container. The method does not throws an exception when the Queue is empty, it returns null instead.
Syntax:
Java
Java
Java
Java
Java
E poll()Returns: This method returns the element at the front of the container or the head of the Queue. It returns null when the Queue is empty. Below programs illustrate poll() method of Queue: Program 1: With the help of LinkedList.
// 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());
}
}
Output:
Program 2: To Demonstrate poll() method of Queue when the Queue becomes empty
Queue: [7855642, 35658786, 5278367, 74381793] Queue's head: 7855642 Queue's head: 35658786
// 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());
}
}
Output:
Program 3: With the help of ArrayDeque.
Queue: [423, 3432] Queue's head: 423 Queue's head: 3432 Queue: [] Queue's head: null
// 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());
}
}
Output:
Program 4: With the help of ConcurrentLinkedDeque.
Queue: [7855642, 35658786, 5278367, 74381793] Queue's head: 7855642 Queue's head: 35658786
// 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());
}
}
Output:
Program 5: With the help of LinkedBlockingDeque.
Queue: [7855642, 35658786, 5278367, 74381793] Queue's head: 7855642 Queue's head: 35658786
// 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());
}
}
Output:
Reference: https://docs.oracle.com/javase/8/docs/api/java/util/Queue.html#poll--
Queue: [7855642, 35658786, 5278367, 74381793] Queue's head: 7855642 Queue's head: 35658786
