Java ScriptEngine call function

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

public class Main {
  public static void main(String[] args) {
    ScriptEngineManager manager = new ScriptEngineManager();
    ScriptEngine engine = manager.getEngineByName("JavaScript");

    // Make sure the script engine implements the Invocable interface
    if (!(engine instanceof Invocable)) {
      System.out.println("Invoking procedures is not supported.");
      return;//from  w w  w. j a  va2 s  .  c om
    }

    // Cast the engine reference to the Invocable type
    Invocable inv = (Invocable) engine;
    try {
      String script = "function add(n1, n2) { return n1 + n2; }";

      // Evaluate the script first
      engine.eval(script);

      // Invoke the add function twice
      Object result1 = inv.invokeFunction("add", 30, 40);
      System.out.println("Result1 = " + result1);

      Object result2 = inv.invokeFunction("add", 10, 20);
      System.out.println("Result2 = " + result2);
    } catch (ScriptException | NoSuchMethodException e) {
      e.printStackTrace();
    }
  }
}