Queue | Java Collections Framework Part -8

Queue is First In First Out (FIFO). First comes first out.

Queue two type
-PriorityQueue
-DeQueue

Methods of Queue Interface
-add(object) or offer(object) - add the elements
-remove() or poll() - remove the elements
-element() or peek() -  it will retrive the top element
-size() - number of elements of queue


Example of Queue Java code.. 

import java.util.Iterator;
import java.util.PriorityQueue;
import java.util.Queue;

public class QueueExample {

    public static void main(String[] args) {

        Queue preQueue = new PriorityQueue();

        preQueue.add("A");
        preQueue.add("B");
        preQueue.add("C");
        preQueue.add("D");
        preQueue.add("E");

        System.out.println("Head: "+preQueue.element());
        System.out.println("Head: "+preQueue.peek());

        Iterator i1 = preQueue.iterator();

        while(i1.hasNext()){
            System.out.println(i1.next());
        }
        System.out.println();

        preQueue.remove();
        preQueue.poll();

        Iterator i2 = preQueue.iterator();

        System.out.println("Aftering removing elements: ");
        while(i2.hasNext()){
            System.out.println(i2.next());
        }
    }

}

Exmple of Deque Java code..

import java.util.*;

public class DeQueueExample {

    public static void main(String[] args) {

        Deque deQueue = new ArrayDeque();

        deQueue.add("A");
        deQueue.add("B");
        deQueue.add("C");
        deQueue.add("D");
        deQueue.add("E");

        System.out.println("Initial size of Deque: "+deQueue.size());

        //get value and does not remove the elements form Deque
        System.out.println("Deque peek: "+deQueue.peek());

        //get first value and remove that object form Deque
        System.out.println("Deque poll: "+deQueue.poll());

        System.out.println("Final size of Deque: "+deQueue.size());

    }

}