Description
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)
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)
Existing
code
—-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.”);
}
Existing code
• 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.
• Finally, submit your files to the grading system.
Existing code
