title: Java - calculating the sum of a series of numbers
body: <p>i am trying to calculate the sum of the first 16 elements of the series 1, 3, 9, 27, 81.... The code does so by first CREATING a suitable instance of Geometric that will be of TYPE Seq.</p>
  
  <pre><code>public class Geometric implements Seq {
  
  private double b;
  public Seq s;
  public double sum;
  
  public Geometric(double a) {
  
      this.b = a;
  }
  
  
  public double valAtIndex(int i) {
      // TODO Auto-generated method stub
      return Math.pow(b, i);
  }
  
  public double total() {
  
      s = new Geometric(3.0);
      for (int a = 0; a &lt; 16; a++) {
  
          int c = -1;
          sum = sum + s.valAtIndex(c = c + 1);
          c++;
  
      }
      return sum;
  }
  
  public double getSum() {
  
      return sum;
  }
  
  public static void main(String[] args) {
  
      System.out.println(sum);
  }
  </code></pre>
  
  <p>}</p>
  
  <p>Not sure if i am doing this the long way round? It isnt working yet, eclipse is saying i need to change the modifier of sum to static?</p>