Calculator Hausaufgabe Projekt - Alpha

public class Calculator {

        public Calculator(){}

        private double r1 = 0;

        public double getR1() {
            return r1;
        }

        public void setR1(double r1) {
            this.r1 = r1;
        }

        private double r2 = 0;

        public double getR2() {
            return r2;
        }

        public void setR2(double r2) {
            this.r2 = r2;
        }

        public void setRegisters(double r1, double r2){
            this.r1 = r1;
            this.r2 = r2;
        }

        public void calculate(int operator){
            calculate(Operator.values()[operator]);
        }

        public void calculate(Operator operator){
            switch(operator){
                case ADD:
                    r1 = r1 + r2;
                    break;
                case SUBSTRACT:
                    r1 = r1 - r2;
                    break;
                case MULTIPlY:
                    r1 = r1 * r2;
                    break;
                case DIVIDE:
                    r1 = r1 / r2;
                    break;
                case SQRT:
                    r1 = Math.sqrt(r1);
                    break;
                case SQRT_N:
                    r1 = Math.pow(r1, 1/r2);
                    break;
                case POW:
                    r1 = Math.pow(r1, r2);
                    break;
                case PERCENT:
                    r1 = r1 * (r2/100);
                    break;
                case CLEAR:
                    r1 = 0;
                    r2 = 0;
                    break;
            }
        }

}


public enum Operator{
    ADD(0),
    SUBSTRACT(1),
    MULTIPlY(2),
    DIVIDE(3),
    SQRT(4),
    SQRT_N(5),
    POW(6),
    PERCENT(7),
    CLEAR(8);

    private int value;
    private Operator(int value){
        this.value = value;
    }
    public int getValue(){
        return this.value;
    }

}

import java.io.*;
class Keyboard{

  public static String readLine(){
      try {
          BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
          return (in.readLine());
      } catch(Exception e) {
          return ("");
      }
  }

  public static double readDouble(){
      double enter = Double.parseDouble(readLine());
      return (enter);
  }

  public static int readInteger(){
      int enter = Integer.parseInt(readLine());
      return (enter);
}

  public static char readChar(){
      char ch =  readLine().charAt(0);
      return (ch);
  }

  public static void writeLine(String value){
      System.out.println(value);
  }

  public static void writeLine(Double value){
      System.out.println(value);
  }

  public static void writeLine(int value){
      System.out.println(value);
  }

  public static void writeLine(float value){
      System.out.println(value);
  }

  public static void writeLine(Object value){
      System.out.println(value);
  }

  public static void writeLine(char[] value){
      System.out.println(value);
  }

  public static void writeLine(boolean value){
      System.out.println(value);
  }

  public static void writeF(String format, Object args){
      System.out.printf(format,args);
  }


}


public class Main {

    public static void main(String[] args) {

        Calculator calc = new Calculator();

        boolean exit = false;

        while (!exit){
            Keyboard.writeLine("");
            Keyboard.writeLine("- OPERATION -");
            for (Operator op : Operator.values()) {
                Keyboard.writeLine(op.getValue() + ". " + op.name());
            }
            Keyboard.writeLine("");
            Keyboard.writeLine("- PARAMETERS -");
            Keyboard.writeLine(Operator.values().length + ". Change the 1st number (VALUE: " + calc.getR1() + ")");
            Keyboard.writeLine((Operator.values().length + 1) + ". Change the 2nd number (VALUE: " + calc.getR2() + ")");
            Keyboard.writeLine("");
            Keyboard.writeLine("- COMMANDS -");
            Keyboard.writeLine((Operator.values().length + 2) + ". Close program");
            Keyboard.writeLine("");
            Keyboard.writeLine("Please, enter the command you wish to execute: ");
            try{
                int selection = Keyboard.readInteger();
                if (selection < Operator.values().length && selection >= 0){
                    calc.calculate(selection);
                }
                else{
                    selection = selection - Operator.values().length;
                    switch (selection){
                        case 0:
                            Keyboard.writeLine("Please, enter a new value for the 1st number:");
                            double value1 = Keyboard.readDouble();
                            calc.setR1(value1);
                            break;
                        case 1:
                            Keyboard.writeLine("Please, enter a new value for the 2nd number:");
                            double value2 = Keyboard.readDouble();
                            calc.setR2(value2);
                            break;
                        case 2:
                            Keyboard.writeLine("Bye! Bye!");
                            exit = true;
                            break;
                        default:
                            Keyboard.writeLine("Command not found");
                            break;
                    }
                }
            }
            catch (Exception e){
                Keyboard.writeLine("Error: " + e.toString());
            }
        }

    }

}