Purpose of this assignment

• To get you started using Swing
• To get you started in Eclipse

General idea of the assignment

You have written thest two classes in assignment 7:

• Fraction -- An object of this class represents a fraction. The class contains methods for operating on the fraction.
• FractionTest -- A JUnit test class for the functions defined in Fraction.

Your assignment this time is to write a GUI (Graphical User Interface), using Swing, to create and display a working calculator for fractions.

Details

Name your project FractionCalculator, your package fractionCalculator, and define your class as class FractionCalculator extends JFrame.

In assignment 7 I did not specify the name of a package, so you probably used a name like fraction, or if you put the tests in a separate package, it might be something like fractionTest or testFractions. Whatever those packages are named, copy them from the earlier assignment and paste them into this assignment. If they were in the default package, create a package or packages to put them in; don't put them in the fractionCalculator package. Do not simply link to those classes; they must be included in your new FractionCalculator project.

Write a GUI that looks like a "real" calculator, the kind you can buy in any drugstore. Except, your calculator will deal only with fractions. It should use a JTextField to display the fractions, and a number of JButtons to do the arithmetic. To prevent the user from typing directly into the display, send the text field the message setEnabled(false).

• You should be able to enter fractions, using JButtons with digits and the / character on them.
• You should be able to do arithmetic, using buttons labeled +, -, ×, and ÷.
  • The characters × and ÷ are not on your computer's keyboard; use new JButton(((char)215) + "") and new JButton(((char)247) + ""), respectively, to create buttons with the correct characters on them.
• Have buttons for negating and inverting the displayed fraction.
• Have buttons to backspace ( (char)8592 ), clear the current entry, and clear all (reset everything).
• There is no = button.

"Real" calculators do all sorts of weird things. For example, entering 2 + = will probably result in 4. To avoid dealing with all kinds of special cases, your fraction calculator should follow some different rules.

• The display should always contain either a fraction, represented as an integer or as numerator/denominator, or it should contain the word Error. If it contains the word Error, the user should not be able to do anything more until the "clear" or "clear all" buttons are clicked.
• The calculator should initially display the number zero, and it should initially have zero (a variable of type Fraction) in "memory".
• When the user begins entering a fraction, it immediately replaces the number in the display. The number that was in the display should be saved in memory, to be used later.
• The user may enter a whole number without a /, or a fraction containing a single /. If the user hits a wrong digit, or a slash in the wrong place, it can be backspaced over.
• "Clear" clears only the display to zero, not the fraction saved in memory, while "clear all" sets both to zero.
• The "invert" and "negate" apply only to the number in the display.
• The four arithmetic buttons, +, -, ×, and ÷, take the number that was saved, apply the operation to that and the number in the display, and put the result in the display. The result should also be saved away in memory.
  • Example: Assume the display is initially 0. If the user enters, 1 / 2 +, then 1/2 is added to 0, and 1/2 is displayed. If the user then enters 1 / 1 0 -, then 1/10 is subtracted from 1/2, and 2/5 is displayed.
  • You do not need to prevent the user from hitting two or three operation keys (+, -, etc.) in a row. If you follow the above rules, the result will be sensible.
• The word Error should be displayed when the user attempts to divide by zero, or tries to use a syntactically incorrect "fraction". Neither of these should affect the number in memory, which must be a legal Fraction at all times.

If you have a question about how the calculator should work, and you don't think it is answered by the above rules, post on Piazza.

Good comments and good style are required, as always. Also, remember you can use SwingExamples.jar for examples of how to do various GUI things.

Due date

Turn in your one zip file to Canvas by 6am Wednesday, November 4.

Notes on submitting your work:

• Please put your name as a comment at the beginning of your program.
• Please do not use non-ASCII characters in your program or in the name of your program or in the name of the folder containing your program.
• Zip your entire project. Do not also zip files within your project. Double-zipping is always a bad idea.