Junit testing for overflow, how to prevent

[Scott Pike]

I don't know if this is the correct forum, but here is my problem. I'm learning and I'm trying to use a test Junit with my method that takes numbers from a collection and gives me an average. I got it to the point where the numbers are taken from the element of the collection and placed in a double variable and added, but one of the Junit test test to see what will happen with an null value in the element.. I tried doing an if(null == smoething ) test but I can seem to figure out what will work. what does the value have to be in for me to compare it and see if it is a null?


Junit

package CIT310;
 
import static org.junit.Assert.*;
 
import java.util.ArrayList;
 
import org.junit.Test;
 
public class StatisticsTest {
 
@Test
public void testAverage() {
ArrayList<Number> aCollection = new ArrayList<Number>();
aCollection.add(5);
aCollection.add(10);
aCollection.add(-5);
double expected = 10.0/3.0;
Double anAverage = Statistics.getAverage(aCollection);
assertEquals(expected, anAverage.doubleValue());


aCollection.clear();
/*
 * checking handling of overflow condition
 */
aCollection.add(4);
aCollection.add(Double.MAX_VALUE);

anAverage = Statistics.getAverage(aCollection);
assertNull(anAverage);

aCollection.clear();
/*
 * checking that null values in the collection are ignored
 */
aCollection.add(null);
aCollection.add(5);
aCollection.add(10);

anAverage = Statistics.getAverage(aCollection);

assertEquals(7.5, anAverage);
/* ch
* checking that Non
*/
ArrayList aList = new ArrayList();
aList.add(new String("hello"));
aList.add(5);

anAverage = Statistics.getAverage(aList);

assertEquals(5.0, anAverage, 0);




}
 
}

My Program

package CIT310;
 
 
import java.util.Collection;
import java.util.Iterator;
public class Statistics {
 
public static Double getAverage(Collection<Number> collection) {
// TODO Auto-generated method stub
Iterator it=collection.iterator();
double sum = 0.0;

int size;
size = collection.size();

while (it.hasNext())
{
Number aNumber = (Number)it.next();
double spaceAmount = aNumber.doubleValue();
Number nullTest = aNumber;
double spaceLeft = Double.MAX_VALUE - sum;
if (spaceLeft <= spaceAmount)
{
System.out.println("There is an error, a double digit has caused" +
"an overflow");
return null;
}
else if(null == nullTest)
{
System.out.println("There is an error, a null value was entered " +
"into the collection of numbers. ");
}
{


 sum = sum +aNumber.doubleValue();
}


}
sum = sum/size;
return sum;
}
 
}

[ September 20, 2007: Message edited by: Jim Yingst ]

[mohsen fakhari]

Hi scott
I read your question but I'm not sure about your poblem.
At first I should say it's hard to understand your code without indentation.
Your code will cause NullPointerException because you should put
sum = sum +aNumber.doubleValue();
in an 'else' statement.
and your 'size' variable shows a wrong value because it consists 'null' values too.

[Scott Pike]

thanks for the thing about my sum addition, but my thing is supposed to contain a null value. This is a testing phase and I am trying to find a way for the program to test to see if an elemen has a null value and then display a message that there is a null value and stopping th program.

in other words, after it gets a null, I want it to test the variable for a null and then give out an error message and stop the program. but so far I havent figured out how to test it for a null.

[Joanne Neal]

The way you are testing for null is correct. The problem is that you get a NullPointerException before you reach the test.

Number aNumber = (Number)it.next();
double spaceAmount = aNumber.doubleValue();   // If aNumber is null, you get a NPE here
Number nullTest = aNumber;
 .
 .
 .
else if(null == nullTest)

[Jim Yingst]

I added code tags to your code to make it more readable; please use these in the future.

I assume you tried running the code above and got a NullPointerException. The stack trace in this exception should tell you which line is causing the problem. As Joanne points out, you need to test for null before the line that's throwing the NullPointerException.