C7X8_AltSum.java

//AltSum.java       MrG     2012.0213
public class AltSum
{
    private int dataSize;
    private double[] data;

    public AltSum(int howMany)
    {
        data = new double[howMany];
        dataSize = 0;
    }

    public void add(double num)
    {
        data[dataSize]=num;
        dataSize++;
    }

    public double getAltSum()
    {
        double sum = 0;
        for(int i=0; i<data.length; i++)
        {
             sum += data[i]*Math.pow(-1,i);
        }
        return sum;
    }

    public double getSum()
    {
        double sum = 0;
        for(int i=0; i<data.length; i++)
        {
             sum += data[i];
        }
        return sum;
    }
}