This goal of this project is to practice handling exceptions. In the first part, you will be writing exception-handling code; in the second part, you will be using exceptions in the context of writing methods.
Clone the repository for this week's lab:
hg clone /cslab/class/csci235/lab7
Bozo the programmer is trying out what he thinks are super efficient or compact versions of methods similar to what we've done before. However, nothing seems to be working. Use exception handling to save the day. For each of the four sections (1-3), uncomment the next part of the main method, find out what exceptions are being thrown, and use that to determine what to catch.
Bozo is particularly excited about his method for summing all the elements in an array. Take a look at it. The method takes a shortcut and skips the loop if it's working on an empty array, and all the adding happens in just one line. He particularly likes how the loop header hardly takes up any space. You try to tell him that this will result in an infinite loop, but he insists that when he has tested it, the loop finishes. Sure, the program crashes, but at least the loop does finish.
Fix sum(int[] array) so that it works correctly,
but do not change or remove any of the lines of code that are already
there (in particular, make sure Bozo's favorite line is untouched).
Instead, just add something around Bozo's favorite line.
Bozo has also written a recursive Fibonacci function. He knows that this recursive version is inefficient, but he doesn't care—it fits all on one line!
Now Bozo is curious... "I wonder what the negative first Fibonacci number is."
When he tries to call fib(-1), something goes
wrong, be he can't tell what because the error message fills the entire screen.
To figure out what the problem is (if you can't guess on your own),
try starting a script file and running the program.
Then exit the script and look at the file using your editor or the command less.
(Typing less filename will display to the screen the contents of
the file called filename; you can scroll through it using the
arrow keys. Use 'q' to quit.)
This time, do not make any changes to the method fib.
Instead, wrap the line that calls fib(-1) with a try and catch.
Bozo has also written an interesting method which he calls rangify.
It takes an array and an integer n and returns the ratio of the value in the
array at n positions before the midpoint to the value in the array at
n positions after the midpoint.
However, he has tried it on several arrays, and it always causes the program
to crash-- in fact, it seems to crash for different reasons every time.
Bozo wants the method fixed so that when it is passed bad parameters it will print a message explaining what is wrong and return the value 0. "But don't use any ifs," Bozo insists.
The three examples in part I are rather odd. Now we'll try using exceptions in a more typical situation of writing the methods of a class.
Look at ArrayOps.java. You need to complete the
missing parts, paying particular attention to throwing and catching
appropriate exceptions. You will be provided with a printed copy of
this code, too.
You have been provided with definitions of several exceptions for your use. The exception classes ArrayStartIndexException, ArrayEndIndexException, ArrayEmptyException, and ArrayNullException are all subclasses of ArrayException.
Script your program's execution. Turn in the typescript and your
source file as lab7.