Computing a string 'calculations'

[Zein Nunna]

Hi guys,

I was trying to comopute a string, such as "32*45-7", I'm unsure how to go about this.
Do I need to break it down and compute each part...? I tried

Integer.parseInt("45*3")    

but is throws an error.

I think my main problem is preserving the operand..? and its position, alot of the calculations have '((' etc..

Any thoughts on how I can tackle something like thingsRegards
Zein

[Joe Ess]

You have to parse the expression keeping in mind operator precedence.
Here is a programming assignment that gives a pseudocode algorithm along with a discussion.

[Zein Nunna]

Hi there,

Thanks for your reply.

I was just wondering, given this is (from my perspective) a very common opeation, is there an libraries that Java provides to evaluate arithmetic expressions.

My calculations at the most will have +/-* and brackets... i.e. - (((5+65)/5) + (16+26/2)? Any ideas..?

Thanks
Zein

[Joe Ess]

Not to my knowledge. Certainly not in the Java SE/EE APIs.
A quick Google search for "infix calculator" returns lots of academic programming assignments. Maybe you could find a library in those results.
[ November 02, 2007: Message edited by: Joe Ess ]

[bart zagers]

This recent thread seems to be about the same problem.

JEP is a commercial library doing this, but that might be a little overkill.

[Zein Nunna]

Hi guys,

Thank you for your responses.

I searched far and wide for an answer and in the end setteled with JEP. See this link http://www.singsurf.org/djep/html/index.html

It does the job perfetley!!

Regards
Zein

[steve souza]

I am currently adding such capabilities to an open source project of mine. I am using antlr to parse the expressions. The learning curve for antlr is a little steep (There is a book by the creator Terrence Parr that is good though), though pretty easy to work with once you get the hang of it.

It would be nice if this was added as part of the java platform.

Here is a link to the antlr grammar that i use to do the math. http://fdsapi.cvs.sourceforge.net/fdsapi/fdsapi/Code/com/fdsapi/parser/FDSMath.g?revision=1.3&view=markup

Here is some usage.

           
import com.fdsapi.parser.FDSMathParser;
 
....
 
public static void main(String[] args) {
double answer=FDSMathParser.calc("((2*3*4)/(2*3*4)+10*(5+5))*.5");
 
answer=FDSMathParser.calc("1/2*.5");
answer=FDSMathParser.calc(".5*1/2");
answer=FDSMathParser.calc(".5*.5");
answer=FDSMathParser.calc("5*(20%3)");
answer=FDSMathParser.calc("5+(22%5*3)"); //mult has precedence over mod
// note you can register call back code that replaces variable names with numbers.
answer=FDSMathParser.calc("abcd * DEfg * _HIJK * _1234 * (10+12) ");

This code is not part of the current release, so if you download the jar it will not work.
[ November 08, 2007: Message edited by: steve souza ]

[Ulf Dittmer]

If I may toot my own horn, the just-published edition of the JavaRanch Journal contains an article by me about how to create real Java classes from user-defined functions at runtime. That's quite a bit faster than using a library like JEP that basically interprets the function.

There are other libraries that come much closer in speed to compiled code, like JEL.