Purposes of this assignment:

• To get you started in creating Graphical User Interfaces (GUIs).
• To give you some experience with the Model-View-Controller design pattern.

Your assignment:

You are to implement a calculator. This calculator has the following features:

• It is integer only (no real numbers).
• It uses the AWT, not Swing.
• It can display (and compute with) numbers in octal, decimal, and hexadecimal.
• It has the standard four functions (add, subtract, multiply, and divide), along with an "=" key.
• It has the standard keys to clear the current entry and to clear everything
• It has three mode buttons, for octal, decimal, and hexadecimal.

I am providing a CalculatorChip class which does all the mathematical operations for you. Your job is to write the GUI for this chip. Download CalculatorChip.java and use it in your project.

Your GUI should include:

• One TextField (for displaying results).
• Sixteen numerical Buttons, labeled 0 through F, for the sixteen hexadecimal digits.
• Buttons for add, subtract, multiply, divide, and equals.
• Buttons to clear the current entry and to clear everything.
• Buttons to set the mode to octal, decimal, or hexadecimal.

These buttons should call appropriate methods in a CalculatorChip object.

In addition, you have the following requirements:

• You should create just one listener to handle all the digit buttons.
• You can provide a separate listener for each of the remaining buttons, or you can use the same listener for more than one button if that simplifies the task.
• Digit buttons that are meaningless in the current base should be made inactive (grayed out). For instance, if the calculator is working in decimal, the buttons A through F should be inactive.
• The text field should be inactive (so the user cannot type into it).

How to get started:

Use BlueJ to create an Applet. You can ignore most of the methods that it creates; the only one of interest in the public void init() method. This is the applet method you will modify to create the GUI. (Of course, you are welcome to create additional methods.) The applet and its init() method provide both the controller (the buttons) and the view (the text field).

In the init() method, create the TextField and the Buttons you will need. Figure out how you will nest containers (Panels), and which layout manager you want to attach to each container. Add all your components (containers included) to the appropriate containers (your Applet, this, is the largest container). You might want to look at RabbitHunt for examples.

Make an instance of the CalculatorChip class. Look at the methods it provides, then attach listeners to your buttons. Each listener should call the appropriate method in the calculator chip, and send the result to the text field. Notice that the calculator chip, which represents the model, does not use your controller or your view; it is completely independent of them.

When you attach one listener to multiple buttons, you need to find out which button caused the listener to be invoked. Remember that the listener gets an ActionEvent object as a parameter, and it contains the information you need.. The ActionEvent class is in the java.awt.event package, and it has two methods, either of which you can use:

• getSource(), inherited from the superclass EventObject, will return the actual object (such as a button) that caused the event. You can compare this object (using ==) with your own buttons.
• getActionCommand() returns the label on the button (as a String).

I strongly recommend that you get the applet working first, then worry about its appearance. Remember that the AWT is fairly primitive. You can choose your layout managers, but you can't tell them what to do. "Not too ugly" may be the best you can achieve. Don't spend a lot of time on appearance and leave "making it work" to the last minute. Functionality is more important than appearance.

Grading:

I expect most students will get 100 on this project. If your applet is particularly nice looking or particularly ugly, you might gain or lose a few points. You can earn some extra credit by adding functionality to the calculator--but do not change its essential nature. It must remain integer only, AWT only, and it must support the given bases.

Red tape:

• This program is due by midnight, Wednesday, November 7.
• Turn in, via Blackboard, a complete ready-to-run BlueJ project.
• Late programs will be penalized 5 points per day and will not be accepted after November 14.
• Extra credit will not be given to any late programs.