how to evaluate and work out(5.0+8.1)*(2.0) in my java program?

Question

I'm creating an arithmetic calculator and need to be able to have it answer a question like (5.0+8.1)x(2.0) so far i have create my subclasses according to each mathematical operation i.e. +,-,x,/. I have got it to work for 2 numbers like 2.0 + 5.0 but i do not understand how i can get it to work for the above expression.

class Addition extends ArithmeticExpression{
    Addition(double value1, double value2){
       result = value1 + value2;
       this.value1 = value1;
       this.value2 = value2;
    }

    public double display() {
       System.out.println("Addition Question Is");
       System.out.println(value1 + " + "+ value2);
       return result;
    }

    public double evaluate(){
       System.out.println("Addition Answer Is");
       System.out.println(result);
       return result;
    }


}

This looks suspiciously like homework. If it is, please tag it as such. — digitaljoel, Nov 17 '11 at 18:55
possible duplicate of [java evaluate string to math expression](http://stackoverflow.com/questions/3422673/java-evaluate-string-to-math-expression) — Ted Hopp, Nov 17 '11 at 18:55
Good approach Dmitry! May not be homework... although it looks a lot like it is. :-) — Costis Aivalis, Nov 17 '11 at 19:14
You're at least the second poster this week to be working on the identical task. The previous questioner's problem was type conversion to int, but it's the same task: write a program in java to evaluate expressions. Coincidental, no? — CPerkins, Nov 17 '11 at 19:46

score 2 · Answer 1 · answered Nov 17 '11 at 18:57

2

This is not as trivial as you might think it is. Forget about the mathematical operations. This is the easy part.

The hard part is to tokenize your input. I suggest reading :

http://www.antlr.org/wiki/display/ANTLR3/Quick+Starter+on+Parser+Grammars+-+No+Past+Experience+Required

http://javadude.com/articles/antlrtut/

answered Nov 17 '11 at 18:57

FailedDev

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I think the difficult part is to understand what are AST-s and how to parse them. It it not only about tokenization, ie lexing. See my answer. – Basile Starynkevitch Nov 17 '11 at 19:01

score 1 · Answer 2 · answered Nov 17 '11 at 19:06

You can find a solution here. This is an article from 1997, so the author uses a Vector. It will give you a deprecation warning when you try to run it. Ignore it first and fix it later.

Here you have a well explained nice C/C++ approach from Siberia. Stick to the description of the solution.

Good luck!

score 0 · Answer 3 · answered Nov 17 '11 at 18:56

0

Create another class for multiplication and then do

 double result = new Multiplication(new Addition(5.0,8.1).evaluate(), 2.0).evaluate();

Is that what you mean?

answered Nov 17 '11 at 18:56

Willem Mulder

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ive got a class for multiplication exactly like the addition class – user1052425 Nov 17 '11 at 19:18

score 0 · Answer 4 · answered Nov 17 '11 at 18:59

0

Learn more about Abstract Syntax Trees (AST), Parsing, Name binding.

answered Nov 17 '11 at 18:59

Basile Starynkevitch

223,805
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score 0 · Answer 5 · answered Nov 17 '11 at 19:07

I'm not going to give code because it's homework, but it might help if you think of it more that every operation operates on two expressions, so in your example (5.0+8.1) your addition operation operates on one constant expression that evaluates to 5.0, and another that has a constant evaluation of 8.1. From there, you can think of your multiplication operation as operating on the (5.0+8.1) expression, and another constant expression that evaluates to 2.0.

how to evaluate and work out(5.0+8.1)*(2.0) in my java program?

5 Answers5