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

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.

? If possible, identify a test case that does not execute the fault. (Reachability)

? If possible, identify a test case that executes the fault, but does not result in an error state.

? If possible identify a test case that results in an error, but not a failure. 

1、(1) Fault：The loop condition should be i>=0 not i>0
(2) x=[ ]; Expected: NullPointerException; Actual: NullPointerException
(3) x=[1,2,3]; y=2; Expected: 1 Actual: 1
(4) x=[1,2,3]; y=4; Expected: -1; Actual: -1

2、(1)Fault：The loop condition should be for (int i=x.length-1; i > 0; i--) not for (int i = 0; i < x.length; i++)
(2)x=null Expected = NullPointerException Actual = NullPointerException
(3)x=[1,2,3]; Expected: -1; Actual: -1
(4)x=[0]; Expected: 0; Actual: 0

第二次作业