El método poll() de Queue Interface devuelve y elimina el elemento en la parte frontal del contenedor. Elimina el elemento en el contenedor. El método no arroja una excepción cuando la Cola está vacía, sino que devuelve un valor nulo .
Sintaxis:
E poll()
Devoluciones: este método devuelve el elemento al frente del contenedor o al principio de la cola. Devuelve nulo cuando la cola está vacía.
Los siguientes programas ilustran el método poll() de Queue:
Programa 1: Con la ayuda de 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());
}
}
Producción:
Queue: [7855642, 35658786, 5278367, 74381793] Queue's head: 7855642 Queue's head: 35658786
Programa 2: para demostrar el método poll() de la cola cuando la cola se vacía
// 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());
}
}
Producción:
Queue: [423, 3432] Queue's head: 423 Queue's head: 3432 Queue: [] Queue's head: null
Programa 3: Con la ayuda de 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());
}
}
Producción:
Queue: [7855642, 35658786, 5278367, 74381793] Queue's head: 7855642 Queue's head: 35658786
Programa 4: Con la ayuda de ConcurrentLinkedDeque .
// 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());
}
}
Producción:
Queue: [7855642, 35658786, 5278367, 74381793] Queue's head: 7855642 Queue's head: 35658786
Programa 5: Con la ayuda de LinkedBlockingDeque .
// 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());
}
}
Producción:
Queue: [7855642, 35658786, 5278367, 74381793] Queue's head: 7855642 Queue's head: 35658786
Referencia: https://docs.oracle.com/javase/8/docs/api/java/util/Queue.html#poll–