java eclipse calculator

finished product from lesson 8, Do-It-Yourself Java Games, by Annette Godtland.

https://drive.google.com/file/d/0B3jCoMOxti9fdmlsWDMtRDdkZ1U/view?usp=sharing


or

package nellie.tobey.calculator;
import com.godtsoft.diyjava.DIYWindow;
public class Calculator extends DIYWindow {
 public Calculator() {
  print("Do some math?");
  String s = input();
  while (s.startsWith("Y")|| s.startsWith("y")) {
  double a = promptForDouble("Enter a number:");
  String operation = promptForString("Enter an operator: * - + / ?");
  double b = promptForDouble("Enter another number:");
  double c = 0;
  switch(operation) {
  case "+":
   c = a + b;
   print(a + "+" + b + "="+ c);
   break;
  case "*":
   c = a * b;
   print(a + "*" + b + "="+ c);
   break;
  case "/":
   try {
   c = a / b;
   print(a + "/" + b + "="+ c);}
   catch (ArithmeticException e) {
    print("can not divide by zero.");
   }
      
   break;
  case "-":
   c = a - b;
   print(a + "-" + b + "="+ c);
   break;
   default:
    print("that is not a valid operator. Try again.");
  
   
  }

  s = promptForString("Do some math?");
  }}
 private double promptForDouble(String prompt) {
  double i = 0;
  print(prompt);
  String s = input();
  try {
   i = Double.parseDouble(s);
  }
  catch (NumberFormatException e) {
   print(s + " is not a valid number. Try again.");
   i = promptForDouble(prompt);
  }
  return i;}
 private String promptForString(String prompt) {
  print(prompt);
  String s = input();
  return s;}

 public static void main(String[] args) {
  new Calculator();
 }
}