How to evaluate a math expression given in string form?

Question

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

• "5+3"
• "10-40"
• "10*3"

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

Answer 1

On JDK1.6, you can try the built-in Javascript algo.

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));

    } 

}