How to parse a mathematical expression given as a string and return a number?

java string parsing math expression

90,503

Solution 1

You can pass it to a BeanShell bsh.Interpreter, something like this:

Interpreter interpreter = new Interpreter();
interpreter.eval("result = 5+4*(7-15)");
System.out.println(interpreter.get("result"));

You'll want to ensure the string you evaluate is from a trusted source and the usual precautions but otherwise it'll work straight off.

If you want to go a more complicated (but safer) approach you could use ANTLR (that I suspect has a math grammar as a starting point) and actually compile/interpret the statement yourself.

Solution 2

i recently developed a expression parser and released it under the apache license. you can grab it at http://projects.congrace.de/exp4j/index.html

hope that helped

Solution 3

You can use the ScriptEngine class and evaluate it as a javascript string

ScriptEngineManager manager = new ScriptEngineManager();
ScriptEngine engine = manager.getEngineByName("js");        
Object result = engine.eval("5+4*(7-15)");

Indeed , yu should know that the result of the following instruction in javascript :

   eval('var aa=5+4*(7-15)')
   aa // -27

There may be a better way, but this one works.

Solution 4

Probably not in as straight forward a manner as you are hoping!

But perhaps you could use a javax.script.ScriptEngine and treat the string as a ECMAScript expression, for example?

Take a look at: Scripting for the Java Platform.

Solution 5

There is no builtin way of doing that. But you can use one of the many many open source calculators available.

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90,503

Martijn Courteaux

I'm writing Java, C/C++ and some Objective-C. I started programming in 2007 (when I was 11). Right now, I'm working on my magnum opus: an iOS, Android, OS X, Linux, Windows game to be released soon on all relevant stores. The game is written in C++ using SDL and OpenGL. A couple of seeds for my name (for java.util.Random, radix 26): 4611686047252874006 -9223372008029289706 -4611685989601901802 28825486102

Updated on November 07, 2020

Comments

Martijn Courteaux over 3 years
Is there a way in Java to get the result from this mathematical expression:
```
String code = "5+4*(7-15)";
```
In other hand what's the best way to parse an arithmetic expression?
sleske over 14 years

That is rather dangerous, as it would allow "script injection" (similar to SQL injection). Proceed with caution.
Andy over 14 years

Good point. I suppose it depends on what the source of the expressions is.
sleske over 14 years

Good idea, but problematic with untrusted input, as it would allow "script injection" (see my other comment).
Nick Holt over 14 years

@sleske: yeah, you'd certainly have to be careful with injection attacks if the string is user entered.
PhiLho over 14 years

Can also use built-in JavaScript (Rhino) interpreter now. Although seems more complex to get an eval. And still have a security risk...
Nick Holt over 14 years

@PhiLho: BeanShell was just something I used a few years ago, but I agree that something based on the javax.script API (I think Rhino is) would be better.
matbrgz over 14 years

+1 for beanshell, being part of the JRE
dreeves almost 14 years

What would this return if the expression were "2/3"? Would it return 0 like Java does? You could stick a typecast in front, but then what about "(2/3)+(1/2)"?
marcolopes about 12 years

Trying to use beanshell... How can i guarantee that the result will always be in DOUBLE type?
Kevin Cooper over 11 years

Beautiful, incredibly simple to use and works great for my needs.
FThompson over 11 years

A regex could be used to strip all "non-math" characters from the input string. Would that secure the application from script injection? (Not planning on using this, but just came across it and it made me curious)
Igor about 10 years

I won't be using this, because I actually need to parse one single expression throughout my application (from a configuration file), but if I had more and couldn't workaround the need, I'd certainly use this! I just had a look at this and it looks amazing (even custom functions are supported!). Great work!
Mat over 9 years

This would fail even with the simple example in the question.
Semioniy over 9 years

Works well for me though.
Mat over 9 years

Might work for you, but doesn't answer the question.
Semioniy over 9 years

There´s always a better way of doing smth - there is no Best way for anything. Hope, you´ll find that useful.
shbi over 8 years

Thanks, I prefer not to have to add dependencies when I don't really need to :D
Mohsen_Fatemi over 7 years

this would fail at a+b*c , there is no priority between operators in this code ...
Abdennour TOUMI almost 7 years

@shbi : it is not an external library, it is built-in javax.script.*
shbi almost 7 years

Understood, but since this expression is being read from an external file, JS engine evaluating arbitrary code is not an option.
John over 3 years

I updated the link. The formula4j tool is now open source.