Homework 2

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

Identity the fault.

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

If possible, identity a test case that does not execute the fault.

x=[ ]; y=2

Expected=-1

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

x=[2,3,5]; y=5

Expected=2

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

x=[2,3,5]; y=1

Expected=-1

---

 

 

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

Identity the fault.

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

If possible, identity a test case that does not execute the fault.

x=[ ]

Expected=-1

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

x=[2]

Expected=-1

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

x=[1,1,1]

Expected=-1