[Java] Expression Evaluation (With Parens)

import java.util.Stack;
import java.util.Scanner;

/* * * * * * * * * * * * * * * * * * * * * * * * * *
 *
 * Description: Evaluation Expression (with parens)
 * Author     : Marco 'RootkitNeo' C.
 * License    : GNU/GPL V.3
 * * * * * * * * * * * * * * * * * * * * * * * * * *
 */


class EvaluateExpression {

  private EvaluateExpression() {}

  // Verifica se il token passato e' un numero
  // @return  true if it's a number; false otherwise
  // (work with negative number)
  // --------------------------------------------------------------------------------
  private static boolean isNumeric(String str)
  {
    return str.matches("-?\\d+(\\.\\d+)?");
  }
  // --------------------------------------------------------------------------------


  // Verifica la priorita' degli operatori
  // @return  true if token1 has a higher priority than token2
  // --------------------------------------------------------------------------------
  private static boolean isHightPriority(String token1, String token2)
  {
    switch(token2)
    {
      case "^":
        if(!token1.equals("^")) return true;
        else return false;
      case "*":
      case "/":
        if(token1.equals("+") || token1.equals("-")) return true;
        else return false;
      case "+":
      case "-":
        return false;
    }

    return false;
  }
  // ---------------------------------------------------------------------------------


  // Parsing Infix Expression
  // @return Postfix Expression
  // ---------------------------------------------------------------------------------
  private static String evaluate(String exp)
  {
    Stack<String> stack = new Stack<String>();
    StringBuilder sb = new StringBuilder();

    Scanner scanner = new Scanner(exp);
    scanner.useDelimiter(" ");

    while(scanner.hasNext())
    {
      String token = scanner.next();

      if(isNumeric(token))
      {
        sb.append(token);
        sb.append(" ");
      }
      else if(!token.equals("(") && !token.equals(")"))
      {
        if(!stack.isEmpty() && isHightPriority(token,stack.peek()))
        {
          sb.append(stack.pop());
          sb.append(" ");
        }
        stack.push(token);
      }
      else if(token.equals("("))
      {
        stack.push(token);
      }
      else if(token.equals(")"))
      {
        String e;

        while(!(e = stack.pop()).equals("("))
        {
          sb.append(e);
          sb.append(" ");
        }
      }
    }

    while(!stack.isEmpty()) sb.append(stack.pop());

    return sb.toString().trim();
  }
  // -----------------------------------------------------------------------------------


  // Parsing Postfix expression
  // @return  number (result)
  // -----------------------------------------------------------------------------------
  public static double calculate(String exp)
  {
    Stack<Double> stack = new Stack<Double>();
    Scanner scanner = new Scanner(evaluate(exp));
    scanner.useDelimiter(" ");

    while(scanner.hasNext())
    {
      String item = scanner.next();

      switch(item)
      {
        case "*":
          stack.push(stack.pop()*stack.pop());
          break;
        case "/":
          stack.push(stack.pop()/stack.pop());
          break;
        case "+":
          stack.push(stack.pop()+stack.pop());
          break;
        case "-":
          stack.push(stack.pop()-stack.pop());
          break;
        case "^": // Non funziona proprio correttamente in alcuni casi, ma l'ho aggiunta comunque
          double f = stack.pop();
          double s = stack.pop();
          stack.push(Math.pow(s,f));
          break;
        default:
          stack.push(Double.parseDouble(item));
      }
    }

    return stack.pop();
  }
  // -------------------------------------------------------------------------------------


}

class TestExp {
  public static void main(String[] args) {
    // This is the correct format of the input string
    System.out.println(EvaluateExpression.calculate("( 1 + 3 * ( 4 ^ 2 ) + ( ( 2 + 3 + 5 ) * 2 + 2 * 4 ) * 2 ) ^ 2"));
  }
}