Regular Expressions in Java - Calculating value to Integer form

Question

I have a string something like : String str="(2+(3*4))+(1+2)"; Somehow I want calculate its value in Integer format. i.e. I should be able to get 2+12+3=17. What matters for me is the End Result.

I used : str.replaceAll("$(.*?)$", "$1"), which doesn't work properly and even I am not able to get the answer as Integer.

Can anyone Help me? Thanks in advance :)

[In computing, a **regular expression** (abbreviated **regex** or **regexp**) is a sequence of characters that forms a search pattern, mainly for use in pattern matching with strings, or string matching, i.e. "find and replace"-like operations.](http://en.wikipedia.org/wiki/Regular_expression) — devnull, Sep 20 '13 at 12:16
This question appears to be off-topic because it is about using regular expressions to perform mathematical tasks. — devnull, Sep 20 '13 at 12:17
possible duplicate of [Evaluating a math expression given in string form](http://stackoverflow.com/questions/3422673/evaluating-a-math-expression-given-in-string-form) — Joe Elleson, Sep 20 '13 at 12:39

Sajal Dutta · Answer 1 · 2013-09-20T12:53:31.123

Shunting-yard algorithm is good for that. Here's a java applet with sourcecode using this algorithm.

For expression evaluations, you can see these libraries-

Janino - This one is really amazing!

Jep Java

Mvel

Using builtin Javascript engine:

import javax.script.ScriptEngineManager;
import javax.script.ScriptEngine;

public class ExpressionEvaluation {

    public static void main(String... args) {

        final ScriptEngineManager mgr = new ScriptEngineManager();
        final ScriptEngine engine = mgr.getEngineByName("JavaScript");

        String expr = "(2+(3*4))+(1+2)";

        try {
            System.out.println(engine.eval(expr)); // prints out 17
        } catch(Exception ex){
            //TODO:  handle the exception
            ex.printStackTrace();
        }

    }
}

Wow, there's a few nice suggestions there - thank you for this answer, Sajal. — vikingsteve, Sep 20 '13 at 12:49

score 3 · Answer 2 · edited May 23 '17 at 12:05

3

Maybe you can use the ScripEngine class in Java and invoke the eval() function to evaluate the expression.

I think this link can help you.

++

edited May 23 '17 at 12:05

Community

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answered Sep 20 '13 at 12:17

Jordan Montel

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score 0 · Answer 3 · edited May 23 '17 at 12:11

0

Check out Jeval

And this question

edited May 23 '17 at 12:11

Community

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answered Sep 20 '13 at 12:20

Aydin

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score 0 · Answer 4 · answered Sep 20 '13 at 12:26

0

Regex is not a good idea for that. You should parse the string and use a stack.

See here for the explanation of the algorithm (the third one): http://www.smccd.net/accounts/hasson/C++2Notes/ArithmeticParsing.html

answered Sep 20 '13 at 12:26

Beleg

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Regular Expressions in Java - Calculating value to Integer form

4 Answers4