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Thepoll() method ofQueue 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 returnsnull instead.Syntax:
E poll()
Returns: This method returns theelement at the front of the container or the head of the Queue. It returnsnull when the Queue is empty.Below programs illustrate poll() method of Queue:Program 1: With the help ofLinkedList.Java
// Java Program Demonstrate poll()// method of Queueimportjava.util.*;publicclassGFG{publicstaticvoidmain(String[]args)throwsIllegalStateException{// create object of QueueQueue<Integer>Q=newLinkedList<Integer>();// Add numbers to end of QueueQ.add(7855642);Q.add(35658786);Q.add(5278367);Q.add(74381793);// print queueSystem.out.println("Queue: "+Q);// print head and deletes the headSystem.out.println("Queue's head: "+Q.poll());// print head and deleted the headSystem.out.println("Queue's head: "+Q.poll());}}
Output:
Queue: [7855642, 35658786, 5278367, 74381793]Queue's head: 7855642Queue's head: 35658786
Program 2: To Demonstrate poll() method of Queue when the Queue becomes emptyJava
// Java Program Demonstrate poll()// method of Queue when the Queue becomes emptyimportjava.util.*;publicclassGFG{publicstaticvoidmain(String[]args)throwsIllegalStateException{// create object of QueueQueue<Integer>Q=newLinkedList<Integer>();// Add numbers to end of QueueQ.add(423);Q.add(3432);// print queueSystem.out.println("Queue: "+Q);// print head and deletes the headSystem.out.println("Queue's head: "+Q.poll());// print head and deleted the headSystem.out.println("Queue's head: "+Q.poll());// print queueSystem.out.println("Queue: "+Q);// print null as Queue is empty nowSystem.out.println("Queue's head: "+Q.poll());}}
Output:
Queue: [423, 3432]Queue's head: 423Queue's head: 3432Queue: []Queue's head: null
Program 3:With the help ofArrayDeque.Java
// Java Program Demonstrate poll()// method of Queueimportjava.util.*;publicclassGFG{publicstaticvoidmain(String[]args)throwsIllegalStateException{// create object of QueueQueue<Integer>Q=newArrayDeque<Integer>();// Add numbers to end of QueueQ.add(7855642);Q.add(35658786);Q.add(5278367);Q.add(74381793);// print queueSystem.out.println("Queue: "+Q);// print head and deletes the headSystem.out.println("Queue's head: "+Q.poll());// print head and deleted the headSystem.out.println("Queue's head: "+Q.poll());}}
Output:
Queue: [7855642, 35658786, 5278367, 74381793]Queue's head: 7855642Queue's head: 35658786
Program 4:With the help ofConcurrentLinkedDeque.Java
// Java Program Demonstrate poll()// method of Queueimportjava.util.*;importjava.util.concurrent.ConcurrentLinkedDeque;publicclassGFG{publicstaticvoidmain(String[]args)throwsIllegalStateException{// create object of QueueQueue<Integer>Q=newConcurrentLinkedDeque<Integer>();// Add numbers to end of QueueQ.add(7855642);Q.add(35658786);Q.add(5278367);Q.add(74381793);// print queueSystem.out.println("Queue: "+Q);// print head and deletes the headSystem.out.println("Queue's head: "+Q.poll());// print head and deleted the headSystem.out.println("Queue's head: "+Q.poll());}}
Output:
Queue: [7855642, 35658786, 5278367, 74381793]Queue's head: 7855642Queue's head: 35658786
Program 5: With the help ofLinkedBlockingDeque.Java
// Java Program Demonstrate poll()// method of Queueimportjava.util.*;importjava.util.concurrent.LinkedBlockingDeque;publicclassGFG{publicstaticvoidmain(String[]args)throwsIllegalStateException{// create object of QueueQueue<Integer>Q=newLinkedBlockingDeque<Integer>();// Add numbers to end of QueueQ.add(7855642);Q.add(35658786);Q.add(5278367);Q.add(74381793);// print queueSystem.out.println("Queue: "+Q);// print head and deletes the headSystem.out.println("Queue's head: "+Q.poll());// print head and deleted the headSystem.out.println("Queue's head: "+Q.poll());}}
Output:
Queue: [7855642, 35658786, 5278367, 74381793]Queue's head: 7855642Queue's head: 35658786
Reference:https://docs.oracle.com/javase/8/docs/api/java/util/Queue.html#poll--

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