Project 8: Another calculator

The goal of this project is to put the state pattern to use.

1. Introduction

You will be writing one last calculator program for this class. This time we'll be back to a normal calculator. But this time you will be encorporating what we learned about the state pattern in your design of the calculator.

2. Setup

In this project you will use the same GUI and other starter code as the other calculator projects.

cp -r ~tvandrun/Public/cs245/proj2/* .

3. Calculator details

Now you'll be operating under the following rules:

• No using ifs, switchs, exception handling, or degenerage loops. All decisions must be done using polymorphism, except when dealing with division by zero or screen formatting-- for those you may use either an if or exception handling.

  (What's a "degenerate loop"? Something like this:

  // I want to check is x < 3 but I can't use an if.
  // I'll use a while loop instead. I'm so clever...
  
  while (x < 3) {
      System.out.println("Now I know that x is less than three!!!");
      break;   // ok, break out of this "loop"
  }
  

  Generally, the point of all this is not to find sneaky ways to build the equivalent of ifs but to use polymorphism.)

• Follow the same specification for the operation of the calculator as from project 2 (see below).
• Use the state pattern to govern the behavior of the calculator.

4. Other requirements and helpful information

Here are the requirements from project 2, repeated here verbatim:

Make this program work just like a hand-held four-function calculator. You can find a decent example for reference here. Don't try to implement anything fancy; don't use Ubuntu's built-in calculator as a reference.

ConcreteCalculatorFace has a constructor that takes no parameters (as used in the example above). A window automatically appears. I've worked on the window so that it appears nicely on the machines in the lab. If you work on this project on your own computer, the window's size might not be right (it isn't, for example, on my Macintosh). You can either adjust it by mouse whenever you run the program, or you can play around with the variables WINDOW_Y_POSITION etc at the beginning of the class ConcreteCalculator. Repeat: This is the only reason you would have to modify the file ConcreteCalculator.java.

In this project, you want your program to work like a real-life hand-held calculator. This is actually pretty hard to do. Even the best students rarely get full marks on the first try of this project. (Calculators will be a recurring theme in the projects of this course.)

Specifically, here are some expectations for your calculator:

• After the equals sign is pressed, the user can either build on the result (by pressing an operation key) or start over (by pressing a number key). So, if the user keys in 3 + 5 = + 8 + 2 =, then the displayed result will be 18 (after the first = is pressed, it will display 8; after the third + is pressed, it will display 16). If, on the other hand, the user keys in 3 + 5 = 8 + 2 =, the final displayed result will be 10.
• The clear button C should reset the calculator at any time.
• Your program shoule not crash on division by zero. Either an error message should be displayed or the calculator should reset.
• The screen should not overflow. For example, if the user keys in 1 / 9, the answer should be rounded so that it fits in the calculator's screen.

Hint: Don't try to write this entire project at once. Start implementing the number buttons first, making numbers appear on the screen. Then implement the plus button. When that's working, start doing the other operator buttons.

Important: The "screen" on the calculator is only 15 characters wide. Java displays double numbers using more than 15 characters. Make sure that when you display results that you do not run off the end of the screen. You need to think about how to format your results. There are several ways to do this. One way is to use the DecimalFormat class; it's described in Absolute Java (check the index, pages differ with edition) or the Java API. You also can devise your own formating strategy using String manipulation.

Also, be sure your code is documented according to the specifications given in the style principles.

5. Reminder about setup()

(Largely repeated from project 5)

To clarify one part of the framework for this and other calculator projects, please note that when your submission is graded, your setUpCalculator() method will be called, and it will be given an object implementing the CalculatorFace interface you are given, but it will not be an instance of the ConcreteCalculatorFace class. ConcreteCalculatorFace is given for your own testing purposes. That is why your code should not be dependent on that class, only on the interface. Also, the main method of SetUp will not be called, only the setUpCalculator() method. In short, the contract you need to fulfill is

6. To turn in

Please turn in all the files you wrote or modified (ie, the files you didn't modify don't need to be turned in) to a turn-in directory. To turn in a specific file, do

cp (some file) /cslab.all/ubuntu/cs245/turnin/(your user id)/proj8

DUE: Wednesday, April 29, 5:00 pm. Note that if still have your two late days, then this makes Friday, Dec 12 (the last day of classes) the effective due date. Moreover, this project overlaps with project 9 (which will be a short project); project 9 will be due May 1, and no late days may be applied to project 9.