Consider a new kind of queue that allows only a single copy of an object in the

Question

Consider a new kind of queue that allows only a single copy of an object in the queue. If an object is added to the queue, but it is already there, leave the queue unchanged. This queue has another operation moveToBack that takes an object in the queue and moves it to the back. If an object is not in the queue, the operation adds it at the back of the queue.

Create an interface NoDuplicatesQueueInterface that extends QueueInterface and save as NoDuplicatesQueueInterfaceYourLastName.java. Then write an array-based implementation of NoDuplicatesQueue and save as NoDuplicatesQueueYourLastName.java. Finally, write a program that adequately demonstrates your new class and save asDriverYourLastName.java.

Here is the QueueInterface.java file:

Explanation / Answer

import java.util.*;

public interface NoDupQueueInterface<T> extends QueueInterface<T>
{

private T[] queue = new T[DEFAULT_CAPACITY];
private int front = 0;
private int back = 0;
private static final int DEFAULT_CAPACITY = 20;
  
   public NoDupQueueInterface()
       {
       this(DEFAULT_CAPACITY);
       }
  
   public NoDupQueueInterface(int initialCapacity)
       {
       @SuppressWarnings("unchecked")
       T[] tempQueue = (T[]) new Object[initialCapacity + 1];
       queue = tempQueue;
       front = 0;
       back = initialCapacity;
       }
  
   public boolean duplicateTest(T newEntry)
       {
       if (size == queue.length)
       throw new IllegalStateException();
       else
           {
           for(int i=0; i<queue.length; i++)
               {
               if(queue[i] == newEntry)
                   {
                   System.out.println("Im not doing anything, youre already in line " + newEntry + "!");
                   return true;
                   }//end if
               else  
                   {
                   System.out.println("Youre not in line yet...I will add you at the back!");
                   return false;   
                   }//end else
               }//end for
           }//end else
       }//end duplicateTest
  
   public void enqueue(T nonDupEntry)
       {
       boolean dupTest = duplicateTest(nonDupEntry);
           if(dupTest==true)
               {
               // Add to rear
               size ++;
               queue[back] = nonDupEntry;
               back ++;
               // If at end of array, wrap around
               if (back == queue.length)
               back = 0;
               }//end if
           else
               System.out.println("Sorry that number is already in line");      
       }//end enqueue
}//end class

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