Thread: Circular Array

Good day im really struggling to see what is wrong with my code any help would be awesome.

public class RingBuffer {
 
    public double[] rb;          // items in the buffer
    private int first;            // index for the next dequeue or peek
    private int last;             // index for the next enqueue
    private int size;   
    private int Capacity;// number of items in the buffer
 
    // create an empty buffer, with given max capacity
    public RingBuffer(int capacity) {
        rb = new double[capacity];
        for(int k = 0;k < capacity;k++)
        {
        	rb[k] = 0;
        }
        first = 0;
        last = 0;
        size = 0;
        Capacity = capacity;
    }
 
    // return number of items currently in the buffer
    public int size() 
    {  	
    	if((first == last) && (rb[first] ==0))
    	{
    	size = 0;
    	return size;
    	}
 
    		size = (last - first);
 
    			if (size < 0)
    			{
    			size += Capacity;
    			}
    		size++;
    		return size;
    		}
 
 
    // is the buffer empty (size equals zero)?
    public boolean isEmpty()
    {
    	if(size() ==0)
    		return true;
    	else return false;
 
    }
    // is the buffer full (size equals array capacity)?
    public boolean isFull() 
    {
    	if(size() == (Capacity)) return true;
    	else return false;
    }
 
    // add item x to the end
    public void enqueue(double x) {
        if (isFull()) {
            throw new RuntimeException("Ring buffer overflow");
        }
      if(isEmpty())
      {
      rb[0] =x;
      }
      else if(last == Capacity-1)
      {
      last = 0;
      rb[0]=x;
      }
      else
      {
      last++;
      rb[last] =x;
      }
    }
 
    // delete and return item from the front
    public double dequeue() {
        if (isEmpty()) {
            throw new RuntimeException("Ring buffer underflow");
        }
     double temp = rb[first];
     rb[first] = 0;
 
 
     if (first ==( Capacity-1))
     { 
     first =0;
     }
     else
     {
     first++;
     }
     return temp;
    }
 
    // return (but do not delete) item from the front
    public double peek() {
        if (isEmpty()) {
            throw new RuntimeException("Ring buffer underflow");
        }
     return rb[first];
    }
 
    // a simple test of the constructor and methods in RingBuffer
 
 
    public static void main(String[] args) {
        int N = 10;
        RingBuffer buffer = new RingBuffer(N);  
        for (int i = 1; i <= N; i++) {
            buffer.enqueue(i);
        }
        double t = buffer.dequeue();
        buffer.enqueue(t);
        System.out.println("Size after wrap-around is " + buffer.size());
        while (buffer.size() >= 2) {
            double x = buffer.dequeue();
            double y = buffer.dequeue();
            buffer.enqueue(x + y);
        }
        System.out.println(buffer.peek());
    }
//output should be Size after wrap-around is 10
    //    55.0 
 
 
}

Originally Posted by KobusJordaan

...struggling to see what is wrong

//output should be Size after wrap-around is 10
    //    55.0

My suggestion: Instrument your code so that the program can tell you what it is seeing and what it is doing:

        System.out.println("Size after wrap-around is " + buffer.size()); // Where things start to go wrong
        while (buffer.size() >= 2) {
            System.out.println("\nIn loop: size is " + buffer.size()); // Debugging code is verbose enough to give some useful information
            double x = buffer.dequeue();
            System.out.println("Size after one dequeue  is " + buffer.size());
            double y = buffer.dequeue();
            System.out.println("Size after two dequeues is " + buffer.size());
            buffer.enqueue(x + y);
            System.out.println("Size after one enqueue  is " + buffer.size());
        }