Question

1. Using the following code identify the fault.

2. Using the following code indentify a test case that results in an error, but not a failure.

public static int lastZero (int[] x) {

//Effects: if x == null throw NullPointerException

//else return the index of the last 0 in x.

//Return -1 if 0 does not occur in x

for (int i = 0; i < x.length; i++)

{

if (x[i] == 0)

{

return i;

}

}

return -1;

}

//test: x = [0, 1, 0]

// Expected = 2

Answer 1

Here is code:

public static int lastZero (int[] x) {
//Effects: if x == null throw NullPointerException
//else return the index of the last 0 in x.
//Return -1 if 0 does not occur in x
if(x == null)
throw new NullPointerException("The x is null");
else
{
//loops from last index to 0th index
for (int i = x.length - 1; i >= 0; i--)
{
if (x[i] == 0)
{
return i;
}
}
return -1;
}
}

Sample test case to run:

public class testCase {
public static void main(String []args){
int[] a = {0,1,0};
System.out.println(lastZero(a));
}
public static int lastZero (int[] x) {
//Effects: if x == null throw NullPointerException
//else return the index of the last 0 in x.
//Return -1 if 0 does not occur in x
if(x == null)
throw new NullPointerException("The x is null");
else
{
//loops from last index to 0th index
for (int i = x.length - 1; i >= 0; i--)
{
if (x[i] == 0)
{
return i;
}
}
return -1;
}
}
}

Output:

2