Below are two faulty programs. Each includes a test case that results in failure.

Answer the following questions (in the next slide) about each program.

(1) Identify the fault.

(2) If possible, identify a test case that does not execute the

fault. (Reachability)

(3) If possible, identify a test case that executes the fault, but

does not result in an error state.

(4) If possible identify a test case that results in an error, but

not a failure

1.

public int findLast (int[] x, int y) {

//Effects: If x==null throw

NullPointerException

// else return the index of the last element

// in x that equals y.

// If no such element exists, return -1

for (int i=x.length-1; i > 0; i--)

{

if (x[i] == y)

{

return i;

}

}

return -1;

}

// test: x=[2, 3, 5]; y = 2

// Expected = 0

(1)it will not check the first element,if only the first is equle to y it will return -1

(2)if y=1 the case: [0 2 1]

(3)if y=1 the case: [0 2 3]

(4)if y=1 the case: [1 2 3]

2.

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

(1)it will show the first zero not the last

(2)case: [0 1 2]

(3)case: [1 2 3]

(4)case: [0 0 0]