How to evaluate a math expression given in string form?

Question

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

1. "5+3"
2. "10-4*5"
3. "(1+10)*3"

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

Answer 1

With JDK1.6, you can use the built-in Javascript engine.

import javax.script.ScriptEngineManager;
import javax.script.ScriptEngine;
import javax.script.ScriptException;

public class Test {
  public static void main(String[] args) throws ScriptException {
    ScriptEngineManager mgr = new ScriptEngineManager();
    ScriptEngine engine = mgr.getEngineByName("JavaScript");
    String foo = "40+2";
    System.out.println(engine.eval(foo));
    } 
}