Question

Step 3

Develop the following class:

Class

Name: ImprovedQueue<T>

Access Modifier: public

Implements: QueueInterface<T>

Instance variables

Name: front

Access modifier: private

Data type: QueueNode<T>

Constructors:

Name: ImprovedQueue

Access modifier: public

Parameters: none (default constructor)

Task: sets the value of front to null

Methods

Name: isEmpty

Access modifier: public

Parameters: none

Return type: boolean

Task: returns true if the front is equal to null; otherwise return false

Name: dequeue                          

Access modifier: public

Parameters: none

Return type: T (parameterized type)

Task: makes a call to the isEmpty method to see if the queue is empty and if it is return null without changing the queue; otherwise removes the front element from this queue and returns it.

Name: enqueue

Access modifier: public

Parameters: element (data type T, parameterized type)

Return type: void

Task: creates a newNode (data type QueueNode<T>) by passing the element parameter to the constructor of the QueueNode<T> class. Then it makes a call to the isEmpty method to see if the queue is empty; if it is it sets value of front to the value of newNode; otherwise it adds it to the rear of the queue. (Note: The rear of the queue is not kept explicitly by an instance variable but it can be found by finding the last node in the queue.)

Answer 1

• Imporoved class is public and it implemets the interface QueueInterface<T>
• The class will have one instance variable: QueueNode<T> front;
• There will be one constructor:
  • This constructor will be default and sets front to null
• There are three methods:
  • isEmpty(): check if front is null or not
  • dequeue(): sets front = front.link
  • enqueue(): add a QueueNode<T> elements at the end of list.

implentation:

constructor:
public ImprovedQueue(){
       this.front = null;
   }

isEmpty():

public boolean isEmpty(){
       if(this.front==null)
           return true;
       else
           return false;
   }

dequeue():
public T dequeue(){
       if(isEmpty())
           return null;
       QueueNode<T> temp = front;
       front = front.getLink();
       temp.setLink(null);
       return temp.getInfo();
   }

enqueue():
public void enqueue(T element){
       QueueNode<T> newNode = new QueueNode<T>(element);
       if(isEmpty())
           this.front = newNode;
       else{
           QueueNode<T> temp = front;
           while(temp.getLink()!=null)
               temp = temp.getLink();
           temp.setLink(newNode);
       }
   }

The complete class:

public class ImprovedQueue<T> implements QueueInterface<T>{
   private QueueNode<T> front;
   public ImprovedQueue(){
       this.front = null;
   }
   public boolean isEmpty(){
       if(this.front==null)
           return true;
       else
           return false;
   }
   public T dequeue(){
       if(isEmpty())
           return null;
       QueueNode<T> temp = front;
       front = front.getLink();
       temp.setLink(null);
       return temp.getInfo();
   }
   public void enqueue(T element){
       QueueNode<T> newNode = new QueueNode<T>(element);
       if(isEmpty())
           this.front = newNode;
       else{
           QueueNode<T> temp = front;
           while(temp.getLink()!=null)
               temp = temp.getLink();
           temp.setLink(newNode);
       }
   }
}