Activity: Exception Handling Solution

Goals:

By the end of this project you should be able to do the following:

    • Handle exceptions that can occur in your program using a try-catch statement

    • Throw exceptions in your program

Directions:

Don’t forget to add your Javadoc comments for your classes, constructor, and methods in this activity.

For this assignment, you will be creating two classes: Division and DivisionDriver

Division: methods

    • Division has two public static methods:

    o intDivide: takes two int parameters (a numerator and denominator), performs integer division, and returns the int result of dividing the numerator by the

denominator.

        o decimalDivide: takes two int parameters (a numerator and denominator), performs floating point division (you'll have to use casting), and returns the result of dividing the numerator by the denominator.

    • Test your methods in the Interactions pane:

Division.intDivide(10, 3)


3
Division.decimalDivide(10, 3)

3.3333333333333335



DivisionDriver

    • DivisionDriver contains a main method only. The program will get a numerator and denominator from the user and print the integer division and decimal division result.

    • Create a dialog box that will get the numerator and denominator as a String (you'll have to import the JOptionPane class in the javax.swing package):










    • Convert each to an integer value using the static parseInt method in the Integer class:







Page 1 of 5
Activity: Exception Handling    Page 2 of 5


    • Create a String object to hold the result of the division:







    • Print the result in a dialog box:






    • Test your method by running the driver program with numerator 19 and denominator 5:






















    • Now try entering an invalid number in the dialogs (five and ten):











Your program should generate a run-time error in the form of a NumberFormatException exception:
----jGRASP exec: java DivisionDriver


Exception in thread "main" java.lang.NumberFormatException: For input string: "five" at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65) at java.lang.Integer.parseInt(Integer.java:580)
at java.lang.Integer.parseInt(Integer.java:615)
at DivisionDriver.main(DivisionDriver.java:9)

----jGRASP wedge: exit code for process is 1.

----jGRASP: operation complete.



Page 2 of 5
Activity: Exception Handling    Page 3 of 5


    • The exception occurs when the parseInt method tries to convert the String "five" to an integer. The Java API listing for parseInt lists the exception that it might throw.

    • Use a try-catch statement to catch the exception and tell the user what went wrong without creating a run-time error:


Existing

code
















    • Try entering invalid values five and ten once more for numerator and denominator once more. You should now get the following error:









Exception Throwing

    • Try the following in the interactions pane:

Division.intDivide(10, 0)


java.lang.ArithmeticException: / by zero


    • Try to run your driver program with the numerator 10 and denominator 0:












----jGRASP exec: java DivisionDriver


Exception in thread "main" java.lang.ArithmeticException: / by zero at Division.intDivide(Division.java:7)

at DivisionDriver.main(DivisionDriver.java:12)


Page 3 of 5
Activity: Exception Handling
Page 4 of 5







----jGRASP wedge: exit code for process is 1.


----jGRASP: operation complete.





    • The exception is generated in the intDivide method and not caught/handled, so it is propagated to main where it is also not caught/handled. Next we want to catch the exception in the intDivide method so that it will not be propagated to the main method.

    • In your intDivide method, add code that will return 0 if an ArithmeticException occurs and the division result otherwise:

Existing code











Run DivisionDriver with inputs 10 and 0. The result should be 0 for integer division:













    • Suppose that you do not want users to be able to divide by 0 in your decimalDivide method.

Division.decimalDivide(10, 0)


Infinity


The IllegalArgumentException in the Java API can be thrown if a particular argument

(parameter) to a method is not allowed:

http://download.oracle.com/javase/6/docs/api/java/lang/IllegalArgumentException.html

    • In your decimalDivide method, throw an IllegalArgumentException if the denominator is zero:

if (denom == 0) {

throw new IllegalArgumentException("The denominator "

+ "cannot be zero.");

}



Page 4 of 5
Activity: Exception Handling    Page 5 of 5


    • Test your method again in interactions. You should now see the exception:

Division.decimalDivide(10, 0)


java.lang.IllegalArgumentException: The denominator cannot be zero.


    • In your main method, add another catch statement to catch the exception that is thrown by the decimalDivide method. This time, print the exception text itself (stored by variable errorMessage):









Existing code



    • Now try dividing by 0 in your program. You will get the following error message instead of a run-time error:





















    • Run Checkstyle on each of your files and make any necessary corrections indicated by audit errors.

    • Finally, submit your files to the grading system.












Page 5 of 5