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I am trying to write a program that reads a sequence of integers into an array and that computes the alternating sum of all elements in the array. For example, if the program is executed with the input data

1 4 9 16 9 7 4 9 11
then it computes

1 - 4 + 9 - 16 + 9 - 7 + 4 - 9 + 11 = - 2

I have below code so far:

```import java.util.Arrays;

/**
This class computes the alternating sum
of a set of data values.
*/
public class DataSet
{
private double[] data;
private int dataSize;

/**
Constructs an empty data set.
*/
public DataSet()
{
final int DATA_LENGTH = 100;
data = new double[DATA_LENGTH];
dataSize = 0;
}

/**
Adds a data value to the data set.
@param x a data value
*/
{
if (dataSize == data.length)
data = Arrays.copyOf(data, 2 * data.length);
data[dataSize] = x;
dataSize++;
}

/**
Gets the alternating sum of the added data.
@return sum the sum of the alternating data or 0 if no data has been added
*/
public double alternatingSum()
{
. . .
}
}

I have to use the following class as the tester class:

/**
This program calculates an alternating sum.
*/
public class AlternatingSumTester
{
public static void main(String[] args)
{
DataSet data = new DataSet();

double sum = data.alternatingSum();
System.out.println("Alternating Sum: " + sum);
System.out.println("Expected: -2.0");
}
}```
Posted 6-Apr-12 19:04pm
Updated 6-Apr-12 22:00pm
JF201555.4K
v3

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## Solution 1

We do not do your homework: it is set for a reason. It is there so that you think about what you have been told, and try to understand it. It is also there so that your tutor can identify areas where you are weak, and focus more attention on remedial action.

Try it yourself, you may find it is not as difficult as you think!

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