Queue array implementation resize

Question

I was required to create a simple queue array implementation with basic methods as enqueue, dequeue, isEmpty, and stuff like that. My only problem is that Im stuck when it comes to the resize method, because if I want to add more values to my queue (with fixed size because is an array) I do not know how to make it work and keep all the values in place. Everything works just in case you were wondering, the only thing is that doesnt work is my resize (the method wrote in here wasn't the only one I tried). I'm going to put my main method as well if you want to try it, hope you can help, thanks.

Main Method:

  public class MainQueue {
              public static void main(String[] args) {

            int capacity=10;
            Queue<Integer> queue = new Queue<Integer>(capacity);

            queue.enqueue(1);
            queue.enqueue(2);
            queue.enqueue(3);
            queue.enqueue(4);
            queue.enqueue(5);
            queue.enqueue(6);
            queue.enqueue(7);
            queue.enqueue(8);
            queue.enqueue(9);
            queue.enqueue(10);

            System.out.println("Queue: "+ queue);

                            //WORKS SO FAR
                            queue.enqueue(11);
                            //11 is placed at the beginning of the queue  
                            //instead at the end and my last value is null (?)

Class queue:

 import java.util.NoSuchElementException;


 public class Queue <E>{
 private E[] elements;//array in generic
 private int front;//first element or front of the queue
 private int back;//last element or back of the queue
 private int capacity; //capacity of the queue
 private int count; //indicates number of elements currently stored in the queue

        @SuppressWarnings("unchecked")
        public Queue(int size)
        {
            capacity = size;
            count = 0;
            back = size-1;
            front = 0;
            elements =(E []) new Object[size];  //array empty   
        }

    //Returns true if the queue is empty or false
    public boolean isEmpty()
        {
            return count==0;//means its true
        }

    //Add elements to the queue 
    public void enqueue(E item)
        {  
            if(count == capacity) 
            {  
                 resize(capacity*2);
                  // System.out.println("Queue is full");  

             }

            back =(back+1) % capacity;    //example back=(0+1)%10=1
            elements[back]=item;
            //elements[0]=0
            //item=elements[count];
            count++;
            }


    //Public resize
    public void resize(int reSize){
        E[] tmp = (E[]) new Object[reSize];

           int current = front;
           for (int i = 0; i < count; i++)
              {
              tmp[i] = elements[current];
              current = (current + 1) % count;
              }
         elements = tmp;

           }


    //Dequeue method to remove head
    public E dequeue() 
            {
                if(isEmpty())
                    throw new NoSuchElementException("Dequeue: Queue is empty");
                else
                {
                    count--;
                    for(int x = 1; x <= count; x++)
                    {
                        elements[x-1] = elements[x];
                    }
                    capacity--;
                    return (E) elements;
                }
            }

//peek the first element
    public E peek()   
        {
            if(isEmpty())  
               {  
                   throw new NoSuchElementException("Peek: Queue is empty");
               }

               else  
                   return elements[front];
         }


//Print queue as string
     public String toString()    
           {  

           if(isEmpty()) {
               System.out.println("Queue is empty.");
            //throw new NoSuchElementException("Queue is empty");
           }

               String s = "[";  
               for(int i = 0; i <count; i++)  
               {  
                   if(i != 0)  
                       s += ", ";  
                   s = s + elements[i];// [value1,value2,....]  
               }  

               s +="]";  
              return s;  
           }  

       public void delete() {   //Delete everything
           count = 0;
       }
       }

Ups, sorry I wrote queue.enque(11); instead of queue.enqueue(11); — Lilith Deficiency
– Lilith Deficiency, Commented Nov 22, 2013 at 5:15

Hernan Arroyo · Accepted Answer · 2013-11-22 05:39:54Z

1

you forgot to update stuff when resizing: front, capacity and back .

public void resize(int reSize){
    E[] tmp = (E[]) new Object[reSize];

       int current = front;
       for (int i = 0; i < count; i++)
          {
          tmp[i] = elements[current];
          current = (current + 1) % count;
          }
     elements = tmp;
     front = 0;
     back = count-1;
     capacity=reSize;
       }

edited Nov 22, 2013 at 5:39

answered Nov 22, 2013 at 5:34

Hernan Arroyo

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1 Comment

Hernan Arroyo Over a year ago

remember to add amalds bugfix and use capacity on the mod operation :)

amald · Accepted Answer · 2013-11-22 05:32:54Z

1

You have few mistakes in resizing when enqueing item which expand queue.

in resize algorithm current = (current + 1) % count; should be (current + 1) % capacity
You have to change capacity value in resize function capacity = resize;

Why are you changing capacity when dequeing?

answered Nov 22, 2013 at 5:32

amald

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