Queue

Queue is a data structure that supports first in first out (FIFO). Elements that are inserted first are extracted last.

Couple of important method for queue are
1. Enqueue: Add element to queue
2. Dequeue: Remove element from queue.

package queue;

import java.util.ArrayList;

public class Queue {

private ArrayList<Object> queue=new ArrayList<>();

public Queue() {

super();

}

/**

 * Add object to the queue

 * @param o

 */

public void enqueue(Object o){

queue.add(o);

System.out.println("Object added "+o);

}

/**

 * remove object from the queue. 

 * remove only if element is there is queue.

 */

public void dequeue(){

//check the size of the queue before removing element from queue

if(queue.size()>0){

System.out.println("Element removed "+queue.get(0));

queue.remove(0);

}

else{

System.out.println("Queue is empty");

}

}

}

Test Program

package queue;

public class MyQueue {

public static void main(String[] args) {

Queue queue=new Queue();

queue.dequeue();

queue.enqueue("A");

queue.enqueue("B");

queue.enqueue("C");

queue.dequeue();

queue.enqueue("D");

queue.enqueue("E");

queue.dequeue();

queue.dequeue();

queue.dequeue();

queue.dequeue();

queue.dequeue();

}

} 

Result

Queue is empty
Object added A
Object added B
Object added C
Element removed A
Object added D
Object added E
Element removed B
Element removed C
Element removed D
Element removed E
Queue is empty