Variables as commands

Question

I want to be able to use a set of variables that can stand in for mathematical operators. I am attempting to create a calculator as a learning exercise. I figure it would not be good to have the calculation occur every time a button is pressed, so how do I change the operators in a question without containing the calculations in an if statement?

Example

string plus = +;
string equals = =;
public void button_clicked(....)
{
    .....
    7 equals 4 plus 3;

It is not a learning exercise if you ask others to do it for you (and to read your mind w.r.t. what you want first). — arne.b, Feb 21 '13 at 17:04
I'm not really sure what you're asking. What do you mean by "change the operators in a question". What is the question? — aglassman, Feb 21 '13 at 17:04
Read this: http://en.wikipedia.org/wiki/Abstract_syntax_tree and this: http://en.wikipedia.org/wiki/Polish_notation — Christophe Roussy, Feb 21 '13 at 17:07
I'd side-step all this by using the `ScriptEngine` to evaluate the result of the formula. — Andrew Thompson, Feb 21 '13 at 17:12

cowls · Answer 1 · 2013-02-21T17:11:53.110

First question. Why would it not be good to calculate when the button is pressed, much simpler.

If you really want you can use a command pattern and store a list of commands to execute when the user clicks equals.

E.g.

public interface Operation {

    public double execute();

}

public class Add implements Operation {

    private double num1;
    private double num2;

    public Add(double num1, double num2) {
        this.num1 = num1;
        this.num2 = num2;
    }

    public double execute() {
        return num1 + num2;
    }

}

Then each time a button is peressed, you create a new operation and store in list. When equals is pressed you execute each operation passing the result from one to the next.

You will obviously need many more operations.

Variables as commands

Example

1 Answers1