RingBuffer.java

import java.util.*;
import java.lang.RuntimeException;
public class RingBuffer 
{
   private double[] data;          // 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;          // number of items in the buffer
   private int capacity;

   /** create an empty buffer, with given max capacity */
   public RingBuffer(int cap) {
      data = new double[cap];
      capacity = cap; 
      first = 0;
      last = 0;
      size = 0;
   }

   /** return number of items currently in the buffer */
   public int size() {
      return size;
   }

   /** is the buffer empty (size equals zero)? */
   public boolean isEmpty() {
      return(size == 0);
   }

   /** is the buffer full (size equals array capacity)? */
   public boolean isFull() {
      return(first == last && size > 0);
   }

   /** add item x to the end */
   public void enqueue(double x) {
      
      data[last] = x;
      last = (last+1) % data.length;
      size++;
   }

   /** delete and return item from the front */
   public double dequeue() {
      if(size == 0) throw new NoSuchElementException();
      
      double ret = data[first];
      first = ++first % data.length;
      size--;
      return ret;
   }

   /** return (but do not delete) item from the front */
   public double peek() {
      return data[first];
   }

   /** a simple test of the constructor and methods in RingBuffer */
   public static void main(String[] args) {
      int N = 100;
      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());
      
      /*
       * Your program should produce the following output:
       * 
       *  Size after wrap-around is 100
   		5050.0
       */
   }
}