Question

Step 1 Develop the following interface: Interface Name: Queue Interface<T> Access Modifier: public Methods Name: isEmpty Access modifier: public Parameters: none Return type: boolean Name: dequeue Access modifier: public Parameters: none Return type: T (parameterized type) Name: enqueue Access modifier: public Parameters: element (data type T, parameterized type) Return type: void

Answer 1

// QueueInterface.java

public interface QueueInterface<T>
{
public boolean isEmpty();
public T dequeue();
public void enqueue(T element);
}

//end of QueueInterface.java

// QueueNode.java

public class QueueNode<T>
{
   private T info;
   private QueueNode<T> link;
  
   // constructor to set the info to the passed value and link to null
   public QueueNode(T info)
   {
       this.info = info;
       link = null;
   }
  
   // method to set the info
   public void setInfo(T info)
   {
       this.info = info;
   }
  
   // method to return the info
   public T getInfo()
   {
       return info;
   }
  
   // method to set the link
   public void setLink(QueueNode<T> link)
   {
       this.link = link;
   }
  
   // method to return the link
   public QueueNode<T> getLink()
   {
       return link;
   }
}

//end of QueueNode.java

// ImprovedQueue.java

public class ImprovedQueue<T> implements QueueInterface<T>
{
private QueueNode<T> front; // first node of the queue
  
// constructor to create an empty queue
public ImprovedQueue()
{
front = null; // set front to null
}
  
// method that returns true if front is null else false
public boolean isEmpty()
{
return(front == null);
}
  
// method that removes and returns the front element of the queue if queue is not empty, else return null
public T dequeue()
{
if(isEmpty())
return null;
  
T element = front.getInfo(); // get the element stored in front
// set front to node next to this node, thus removing the front element
front = front.getLink();
  
return element;
}
  
  
// method to insert the element at the end of queue
public void enqueue(T element)
{
// create a new node with data as element and next as null
QueueNode<T> newNode = new QueueNode<T>(element);
  
// is the queue is empty, set front to newNode
if(isEmpty())
front = newNode;
else
{
// non-empty queue
// create currNode to front node of the queue
QueueNode<T> currNode = front;
  
// loop to get the last node of queue
while(currNode.getLink() != null)
currNode = currNode.getLink();
  
// set next of last node to newNode to insert element at the end of queue   
currNode.setLink(newNode);   
}
}
  
}
//end of ImprovedQueue.java

// QueueDemo.java

public class QueueDemo {

   public static void main(String[] args) {

       // create a reference of QueueInterface and refer it to the new object of ImprovedQueue
       QueueInterface<String> myQueue = new ImprovedQueue<String>();
      
       // enqueue elements into the queue
       myQueue.enqueue("A");
       myQueue.enqueue("B");
       myQueue.enqueue("C");
       myQueue.enqueue("D");
      
       // remove and set discard to the front element of queue
       String discard = myQueue.dequeue(); // discard contain "A"
      
       // loop that continues till myQueue is not empty
       while(!myQueue.isEmpty())
       {
           String front = myQueue.dequeue(); // remove and get the front element of myQueue
           System.out.println(front); // display the front element returned
       }
      
   }

}

//end of QueueDemo.java

Output:

B с D