Question

Please answer in Java code

Specify the list-based implementation for a enqueue() and dequeue() method of the Queue ADT.

Answer 1

Here i have created 3 java classes. One is interface(Queue.java), and other two are java Classes. LinkedListQueue.java is architecture of queue, and LinkedQueueDemo.java used for perform operation on queue.

/*************************** Queue.java Starts here ********************************/

package com.test.test2;

public interface Queue <Item> extends Iterable <Item>

{

Item dequeue(); // removes an item from the front of the queue

void enqueue(Item item); // adds an item to the rear end of the queue

boolean isEmpty(); // returns true if queue is empty, false otherwise

int size(); // returns the number of items in the queue right now

}

/*************************** Queue.java Ends here ********************************/

/*************************** LinkedQueue.java Starts here ********************************/

package com.test.test2;

import java.lang.Iterable;

import java.util.*;

class LinkedQueue <Item> implements Queue <Item>

{

private Node front, rear; //begin and end nodes

private int size; // number of items

private class Node

{

Item item;

Node next;

}

public LinkedQueue()

{

front = null;

rear = null;

size = 0;

}

public boolean isEmpty()

{

return (size == 0);

}

public Item dequeue()

{

Item item = front.item;

front = front.next;

if (isEmpty())

{

rear = null;

}

size--;

return item;

}

public void enqueue(Item item)

{

Node oldRear = rear;

rear = new Node();

rear.item = item;

rear.next = null;

if (isEmpty())

{

front = rear;

}

else

{

oldRear.next = rear;

}

size++;

}

public int size()

{

return size;

}

public Iterator<Item> iterator()

{

return new LinkedQueueIterator();

}

private class LinkedQueueIterator implements Iterator <Item>

{

private int i = size;

private Node first = front; //the first node

public boolean hasNext()

{

return (i > 0);

}

public Item next()

{

Item item = first.item;

first = first.next;

i--;

return item;

}

public void remove()

{

// not needed

}

}

}

/*************************** LinkedQueue.java Ends here ********************************/

/***************************  LinkedQueueDemo.java Starts here ********************************/

package com.test.test2;

public class LinkedQueueDemo

{

public static void main (String a[])

{

Queue <Integer> q = new LinkedQueue<Integer>();

  

System.out.println("Inserting Items in queue : ");

  

q.enqueue(11);

q.enqueue(22);

q.enqueue(33);

q.enqueue(44);

q.enqueue(55);

q.enqueue(55);

  

System.out.println("Queue after inserting items : ");

for (Integer i : q) {

System.out.println(i);

}

System.out.println("\nDelete an item from queue: " + q.dequeue());   

System.out.println("\nTotal Size of the queue: " + q.size());

System.out.println("\nNow the queue is:");

for (Integer i : q)

System.out.println(i);  

}

}

/***************************  LinkedQueueDemo.java Ends here ********************************/

OUTPUT >>>>>>>>>

Inserting Items in queue :
Queue after inserting items :
11
22
33
44
55
55

Delete an item from queue: 11

Total Size of the queue: 5

Now the queue is:
22
33
44
55
55