Java: Parse a mathematical expression given as a string and return a number

Question

Is there a way in Java to get the result from this mathematical expression:

String code = "5+4*(7-15)";

Ie, what's the best way to parse an arithmetic expression?

Answer 1

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

Answer 2

This may be of help: Parsing an Algebraic Expression

Answer 3

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.

Answer 4

There is no direct support in the Java SDK for doing this.

You will either have to implement it yourself (possibly using a parser generator such as JavaCC), or use an existing library.

One option would be JEP (commercial), another JEval (free software).

Answer 5

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.

Answer 6

You could use Jython's interpreter for that.