Question

Create a new Java file, containing this code

public class DataStatsUser {
    public static void main (String[] args) { 
      DataStats d = new DataStats(6); 
      d.append(1.1);
      d.append(2.1);
      d.append(3.1);
      System.out.println("final so far is: " + d.mean()); d.append(4.1);
      d.append(5.1);
      d.append(6.1);
      System.out.println("final mean is: " + d.mean());
    } 
  }

This code depends on a class called DataStats, with the following API:

public class DataStats {
    public DataStats(int N) {
    }
       // set up an array (to accept up to N doubles) and other member variables
    public double mean() {
        return 0;
    }
       //compute and return the mean of the set of numbers added so far
    public void append(double in) {
    }
       //append number to the set; throw error if more than N numbers added
 }

Your job: implement DataStats, so that it correctly works when used by DataStatsUser.

Answer 1

Below is the solution:

import java.util.ArrayList;

public class DataStatsUser {
   public static void main(String[] args) {
       DataStats d = new DataStats(6);
       d.append(1.1);
       d.append(2.1);
       d.append(3.1);
       System.out.println("final so far is: " + d.mean());
       d.append(4.1);
       d.append(5.1);
       d.append(6.1);
       System.out.println("final mean is: " + d.mean());
   }
}

public class DataStats {
   ArrayList<Double> arrlist; //declare arraylist

   public DataStats(int N) {
       arrlist = new ArrayList<Double>(N); //declare the size of arraylist
   }

   // set up an array (to accept up to N doubles) and other member variables
   public double mean() {
       int sum = 0, i;
       for (i = 0; i < arrlist.size(); i++) { //iterate through loop
           sum += arrlist.get(i); //sum of all the arraylist
       }
       double mean = (float)sum / arrlist.size(); //calculate the mean
       return mean;
   }

   // compute and return the mean of the set of numbers added so far
   public void append(double in) {
       arrlist.add(in); //append the arraylist
   }
   // append number to the set; throw error if more than N numbers added
}

sample output:

final so far is: 2.0
final mean is: 3.5