How to evaluate a math expression given in string form?

user_256082 0
Viewed 569523

I'm trying to write a Java routine to evaluate math expressions from String values like:

  1. "5+3"
  2. "10-40"
  3. "(1+10)*3"

I want to avoid a lot of if-then-else statements. How can I do this?

math java string
25 Answers

External library like RHINO or NASHORN can be used to run javascript. And javascript can evaluate simple formula without parcing the string. No performance impact as well if code is written well. Below is an example with RHINO - 

public class RhinoApp {
    private String simpleAdd = "(12+13+2-2)*2+(12+13+2-2)*2";

public void runJavaScript() {
    Context jsCx = Context.enter();
    Context.getCurrentContext().setOptimizationLevel(-1);
    ScriptableObject scope = jsCx.initStandardObjects();
    Object result = jsCx.evaluateString(scope, simpleAdd , "formula", 0, null);
    Context.exit();
    System.out.println(result);
}
user_11557580 
import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;

public class test2 {
    public static void main(String[] args) throws ScriptException {
        String s = "10+2";
        ScriptEngineManager mn = new ScriptEngineManager();
        ScriptEngine en = mn.getEngineByName("js");
        Object result = en.eval(s);
        System.out.println(result);
    }
}
user_103671780
Related