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

java string parsing math expression
Martijn Courteaux picture Martijn Courteaux · Sep 16, 2009 · Viewed 85.9k times · Source

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?

Answer

Nick Holt picture Nick Holt · Sep 16, 2009

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.

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