Evaluating 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:

1. "15+9"
2. "50-40"
3. "10*4"

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

Answer 1

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 = "45+3";
    System.out.println(engine.eval(foo));
    } 
}