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

Answer 1

There's an open-source tool called formula4j that does that job.

To take your example expression, it would be evaluated like this using formula4j:

Formula formula = new Formula("5+4*(7-15)");

Decimal answer = formula.getAnswer(); //-27

Answer 2

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 3

You coul use that project

How to use:

double result = 0;
String code = "5+4*(7-15)";
try {
    Expr expr = Parser.parse(code);
    result = expr.value();
} catch (SyntaxException e) {
    e.printStackTrace();
}
System.out.println(String.format("Result: %.04f", result));

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).