Question

Define a class of queues that implements the interface QueueInterface, as defined in Listing 7-1 in Chapter 7. Use an instance of the class ArrayList to contain a queues entries. Then write a driver/test program adequately demonstrates your new class. Note that you might have to handle exceptions thrown by methods of ArrayList.

Deliverables:

• EmptyQueueException.java (given in Lab_7_StartUp folder)
• QueueInterface.java (given in Lab_7_StartUp folder)
• ArrayListQueue.java (need to create)
• Lab7.java (need to create)

QueInterface:

@author Frank M. Carrano
@author Timothy M. Henry
@version 5.0
*/
public interface QueueInterface<T>
{
/** Adds a new entry to the back of this queue.
@param newEntry An object to be added. */
public void enqueue(T newEntry);
  
/** Removes and returns the entry at the front of this queue.
@return The object at the front of the queue.
@throws EmptyQueueException if the queue is empty before the operation. */
public T dequeue();
  
/** Retrieves the entry at the front of this queue.
@return The object at the front of the queue.
@throws EmptyQueueException if the queue is empty. */
public T getFront();
  
/** Detects whether this queue is empty.
@return True if the queue is empty, or false otherwise. */
public boolean isEmpty();
  
/** Removes all entries from this queue. */
public void clear();
} // end QueueInterface

EmptyQueueException:

/**
A class of runtime exceptions thrown by methods to
indicate that a queue is empty.
@author Frank M. Carrano
@author Timothy M. Henry
@version 5.0
*/
public class EmptyQueueException extends RuntimeException
{
public EmptyQueueException()
{
this(null);
} // end default constructor

public EmptyQueueException(String message)
{
super(message);
} // end constructor
} // end EmptyQueueException

Answer 1

//QueInterface.java

/**
@author Frank M. Carrano
@author Timothy M. Henry
@version 5.0
*/
public interface QueueInterface<T>
{
/** Adds a new entry to the back of this queue.
@param newEntry An object to be added. */
public void enqueue(T newEntry);
  
/** Removes and returns the entry at the front of this queue.
@return The object at the front of the queue.
@throws EmptyQueueException if the queue is empty before the operation. */
public T dequeue();
  
/** Retrieves the entry at the front of this queue.
@return The object at the front of the queue.
@throws EmptyQueueException if the queue is empty. */
public T getFront();
  
/** Detects whether this queue is empty.
@return True if the queue is empty, or false otherwise. */
public boolean isEmpty();
  
/** Removes all entries from this queue. */
public void clear();
} // end QueueInterface

//EmptyQueueException.java

/**
A class of runtime exceptions thrown by methods to
indicate that a queue is empty.
@author Frank M. Carrano
@author Timothy M. Henry
@version 5.0
*/

public class EmptyQueueException extends RuntimeException
{
public EmptyQueueException()
{
this(null);
} // end default constructor

public EmptyQueueException(String message)
{
super(message);
} // end constructor
} // end EmptyQueueException

//ArrayListQueue.java

import java.util.ArrayList;

public class ArrayListQueue<T> implements QueueInterface<T>
{
   ArrayList<T> arr;
//constructor
public ArrayListQueue()
   {
       arr = new ArrayList<>();
   }
  
   /** Adds a new entry to the back of this queue.
   @param newEntry An object to be added. */
   public void enqueue(T newEntry)
   {
       arr.add(newEntry);
   }
  
   /** Removes and returns the entry at the front of this queue.
   @return The object at the front of the queue.
   @throws EmptyQueueException if the queue is empty before the operation. */
   public T dequeue()
   {
       if(isEmpty())
           throw new EmptyQueueException();
       T entry = arr.get(0);
       arr.remove(0);
       return entry;
   }
  
   /** Retrieves the entry at the front of this queue.
   @return The object at the front of the queue.
   @throws EmptyQueueException if the queue is empty. */
   public T getFront()
   {
       if(isEmpty())
           throw new EmptyQueueException();
       return arr.get(0);
   }
  
   /** Detects whether this queue is empty.
   @return True if the queue is empty, or false otherwise. */
   public boolean isEmpty()
   {
       return arr.size()==0;
   }
  
   /** Removes all entries from this queue. */
   public void clear()
   {
       arr.clear();
   }
}

//Lab7.java

public class Lab7
{
   //main method
   public static void main (String[] args) throws EmptyQueueException
   {
       //create object of ArrayListQueue of integers
       ArrayListQueue<Integer> aq = new ArrayListQueue<>();
       //enqueue 5 items
       for(int i=1; i<=5; i++)
       {
           int x = i*i;
           aq.enqueue(x);
           System.out.println ("Enqueue: " + x);
       }
       //check if queue is empty
       System.out.println ("Is Queue empty? " + aq.isEmpty());
       ///dequeue 3 items
       for(int i=1; i<=3; i++)
       {
           System.out.println ("Dequeue: " + aq.dequeue());
       }
       //check if queue is empty
       System.out.println ("Is Queue empty? " + aq.isEmpty());
       //clear the queue
       System.out.println ("Clear the queue.");
       aq.clear();
       //check if queue is empty
       System.out.println ("Is Queue empty? " + aq.isEmpty());
   }
}

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