The goal of this project is to practice using stacks in an algorithm.
Polish mathematician Jan Lukasiewicz invented a notation for arithmetic where the operator comes before the operands, for example + 5 3 instead of 5 + 3. The advantage of this is that the order of operation is always unambiguous without the need for parentheses (or even precedence rules). For example, 5 * 3 - 9 is written - * 5 3 9, whereas 5 * (3 - 9) is written * 5 - 3 9. In honor of its inventor (or his nationality, at any rate), this is referred to as Polish notation. (It is also called prefix notation, in contrast to normal arithmetic notation which is thus infix.)
Reverse Polish notation is similar except that the operator is put after the operands (so it is also postfix notation). The advantage is that all the operands are then known before the operator is read, if we read the string from left to right. This notation is particularly interesting for our purposes, because a stack can be used to evaluate expressions in RPN. Your task is to write a calculator that evaluates expressions entered in RPN.
In this project you will use the same GUI as in the earlier calculator example. After making the directory for this project, checkout the same files as in Project 2:
cp -r ~tvandrun/Public/cs245/proj2/* .
As before, you will need to implement the method
SetUp.setUpCalculator(),
which takes an object of some class that
implements CalculatorFace and
attaches the other parts of your calculator to that face.
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
WhensetUpCalculator()is given an object implementing the interfaceCalculatorFace, it will instantiate and attach action listeners to the given object (and instantiate any other appopriate classes, ie the "brain" or whatever you call it) so that the given object will behave like a (in this case, RPN) calculator.
One difficulty in using RPN, especially on a simulated hand-held calculator, is how to delimit the operands. The string 937+ could mean 9 + 37 or 93 + 7. In a string, this disambiguation would be done using spaces. For your calculator, you should interpret the "." button as indicating the boundary between numbers. Consequently, your calculator needs to work only on integers; division should be integer division. This also means that you don't have to worry about screen overflow or other formatting. I also won't be checking for how you handle division by zero. Additionally, the equals button is useless-- you do not need to do anything when it is pressed.
Generally this is an easier project than the previous calculator project (and easier than the next calculator project...). The emphasis is not on polishing (heh heh) the calculator's extreme cases but on using the stack.
Even though this section of the course is about data structures, you should keep thinking about object-oriented design. You may have heard that later in this course you will be given a project where you have to write a calculator without any ifs. See if you can reduce the number of if statements you need. (That does not mean that you should replace ifs with swtiches, ?: conditionals, degenerate while loops, or exception handling. It means you should try to replace ifs with polymorphism.)
You should also implement the clear button. This should reset the entire calculator. Moreover, if the user presses the operation buttons when there is not enough information in the stack, your calculator should just ignore it. You calculator should not crash in such a situation.
Please turn in all the files you wrote or modified to the turn-in directory for this project:
cp (some file) /cslab.all/ubuntu/cs245/turnin/(your user id)/proj6
DUE: 5:00 pm Friday, Nov 14. (Note that this overlaps with projects 5 and 7.)