题目：
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.
public intfindLast(int[] x, inty) {
//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 (inti=x.length-1; i> 0; i--)
{
if (x[i] == y)
{
return i;
}
}
return -1;
}
// test: x=[2, 3, 5]; y = 2
// Expected = 0
2.
public static intlastZero(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 (inti= 0; i< x.length; i++)
{
if (x[i] == 0)
{
return i;
}
} return -1;
}
// test: x=[0, 1, 0]
// Expected = 2
(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.
解答：
1.(1)故障为：循环中i的取值应当为i>=0
(2)x=[2,3,5] y=5
(3)x=[2,3,5] y=1
(4)x=[2,3,5] y=2
2.(1)故障为：应当从后往前进行循环，应改为for(int i=x.length-1;i>=0;i--)
(2)x=[1,2,3]
(3)x=[1,0,2]
(4)x=[0,1,0]