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.
A:
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
B:
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
■ Identify the fault.
A: i should be greater than or equal to 0.
B: x should be searched from ending to beginning.
■ identify a test case, does not execute the fault
A: test: x=null; y=4;
B: test: x=null;
■ identify a test case, executes the fault, but does not result in an error state
A: test: x=[ 3,5,6,7,4,3,2,8]; y=4; It contains a 4 of index 4, not index 0;
B: test: x=[0]; It contains only one 0;
■ identify a test case, results in an error, but not a failure
A: test: x=[ 3,5,6,7,2,3,2,8]; y=4; It doesn’t contain a 4;
B: test: x=[ 3,5,6,7,2,3,2,8]; It doesn’t contain a 0;