/**
  * @author  monika heiner
  * @version 1.01
  * @date 14.05.2012
  * @class ExceptionDemo3
  */

// Standard runtime exceptions werden abgefangen und behandelt
// zusaetzlicher Einsatz von nutzer-definierten Exceptions

import java.util.Scanner;
public class ExceptionDemo3 {

	public static void main(String[] argv) {
		int a, b, op;
		double realB;

		System.out.println("willkommen zur wiederholung der grundrechenarten");
		op = getInt("Operationsauswahl: \n"
			+ "  1 -->> add\n"
			+ "  2 -->> sub\n"
			+ "  3 -->> mul\n"
			+ "  4 -->> div\n"
			+ "  5 -->> real div\n"
			+ "  6 -->> exit\n"
			+ "Operation: ");

		while ((op > 0) && (op < 6)) {
			a = getInt("  a: ");
			b = getInt("  b: ");

			try {
				switch (op) {
					case 1 :
						System.out.println("  result: " + (a + b));
						break;
					case 2 :
						System.out.println("  result: " + (a - b));
						break;
					case 3 :
						System.out.println("  result: " + (a * b));
						break;
					case 4 :
						if (b == 0) {
							throw new DivideByZeroException();
						} else {
							System.out.println("  result: " + (a / b));
						} // if
						break;
					case 5 :
						if (b == 0) {
							throw new DivideByZeroException("zero division in real div op");
						} else {
							realB = b;
							System.out.println("result: " + (a / realB));
						} // if
						break;
				} // switch
			} // try
			
			catch (DivideByZeroException e) {
				System.out.println(e + " -> operation skipped");	
			} // catch
			
			catch (Exception e) {
				System.out.println("operation skipped, because <I don't know>");
			} // catch
			
			// finally { <last will> }

			op = getInt("next Operation: ");

		} // while
		System.out.println("auf wiedersehen!");

	} // main
	
	
// Vereinfachung der Eingabe
static int getInt(String message) {
	Scanner in = new Scanner(System.in);
	System.out.print(message);
	return in.nextInt();
} // getInt

} // ExceptionDemo3

//------------------------ cut here into separate files --------------------------------

// definition of a 'throwable object'
// -> any class derived from class Throwable, e.g. Exception or Error
class DivideByZeroException extends ArithmeticException {

	public DivideByZeroException() {
		super("division by zero attempted");
		// string is passed to system's exception system 
		// so that it is available for printing
	}

	public DivideByZeroException(String s) {
		super(s);
	}

} // class DivideByZeroException