CS 3340 OOP

CS 3340 OOP

Exercise 4: Stack: Exceptions
Chapter Readings: TIJ [9]

Goal: To learn how to handle error situations with a modern technique call Exceptions.

Tutorial

Consider this C program and its old style of reporting errors via return code or call-by-reference parameter: except.c

Here is a modern object-oriented way of reporting errors via the Exception class: API: Exception.java

and the corresponding C program written in Java using Exceptions: Except.java

and also a tutorial.

The two key points are:

An area of code might detect an error, but cannot handle the error - maybe it cannot talk to the user at this level - so it delivers the Exception to a higher level. This higher level may handle the error or pass it along to an even higher area of code,
The code starts to look better, without having to worrying about errors at each call. Just make the normal calls inline and, if an error does arise, there is a special block (the "catch") to process the error.

A UML hierarchy of Exception inheritance: ex4a.pdf

That is, programmers can develop their own Exceptions, just like those for SQL or AWT. These exceptions can be thrown and caught at various points in the code.

Here is a design for an example program:

method	action	catch	throw
main(args[0])	call a(i)	ArrayIndexOutOfBoundsException
		NumberFormatException
a(i)	call b(i)	MySubException
		MyException
b(i)	call c(i)	MyOtherException	MyException
c(i)	i=0		MyException
	i=1		MySubException
	i=99		MyOtherException
	default		return i*i

and the program itself: Except1.java

The above is tested with this demo

Assignment

For the first part, you are given this UML hiearchy of Exception inheritance: ex4b.pdf

and the following design:

method	action	catch	throw
main(args[0])		ArrayIndexOutOfBoundsException
		NumberFormatException
	call x(i)	E2
		E1
x(i)	i=1..10	OK
	i=11..20		E1
	default: call y(i)	E3	E1
y(i)	i=21..30	OK
	i=31..40		E2
	default		E3

Code E.java, only class E needs to be public, the Exceptions can just be included in the source.

Put a testing main in E.java similar to the one in Except1.java.

The output should look like demo1

Note the messages printed by demo1 follow these rules:

Each "throw" should state the reason, but not actually print.
Each "catch" should print location: and then a getMessage() from the throw.
OK data just does a println().
Be sure your demo1 runs exactly the same as specified.

Now you're ready for the second part of the assignment.

Copy your Stack.java from Ex1: cp ../ex1/Stack.java .

Recall the Person class from Ex1: Person.java

Modify your Stack.java to handle the error situations where:
1. push() is performed on a full stack
2. pop() is performed on an empty stack

Create your own type of Exception, and be sure to test the pop().

Turn-In: E.java, including commented-out listing of the resultant output. Stack.java, also with output.