COMP1213 - Activity - Exception Handling - Solved

Goals:

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

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

Ø  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:

 
•       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. 

 
•       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:

 

 

•       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) 
 

 ----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:

 

        

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."); 

}

 

•       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):

 

•       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