Assignment 4

Due date: Monday 4/12/04 by 4:00pm

Hand in electronically: POSCalculator.java, questions.txt

Hand in printed copies: POSCalculator.java

This assignment requires you to write a class that reads from a file, does calculations, and writes output to another file, handling exceptions along the way. It’s much smaller than A3, but it uses a lot of new ideas, so again, you can’t leave it to the last couple of days and expect to finish. Here are some things to remember:

1) The POSCalculator class must be instantiable. The main method may do the console I/O required to get filenames from the user, but then it must create a POSCalculator object that does the actual translating from one file to another. So you will need a constructor, some data members, and a couple instance methods.

2) Since you now know how to handle exceptions, your program should be unbreakable. Any exception that could occur should be caught, and something reasonable should be done with it. The program may have to print an apology and exit, but it should never crash.

3) Remember the correct Javadoc commenting style. You don’t have to turn in a separate design for this one, but it would be a good idea to start the same way that you had to for A3, with a comment skeleton.

4) This hint will only make sense after you’ve read the assignment. Suppose you have a file that looks like this:

1.0

+

2.5

=

You’ll be processing one line at a time. When you read “1.0”, you don’t do anything right away, because there’s

no calculation yet. But you’ll have to store the number 1.0 to use later. When you read “+”, you know what

operation you have to do later, so you’ll have to store that knowledge. When you read “2.5”, you finally have a

full operation, and you can use the things you’ve stored along with the 2.5 to make the calculation. When you

read “=” you can print the result of that calculation out.

Here’s the hint: remember that data members are where you store the “state” of an object—information that

you’ll use later. This should give you an idea of some of the data members you’ll need.