/**
  * @author  monika heiner
  * @version 1.01
  * @date 04.04.2002
  * @class ExceptionDemo4
  */

import java.util.Scanner;
public class ExceptionDemo4 {

	// thrown, but not caught exceptions must be reported in a "throws clause"
	// errors and RuntimeExceptions do not need to be listed
	static void operationEvaluation(int op, int a, int b)
		throws DivideByZeroException, OpException {
		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();
				} else {
					double realB = b;
					System.out.println("result: " + (a / realB));
				} // if
				break;
			case 6 :
				System.exit(0);
			default :
				throw new OpException();
		} // switch
	} // operationEvaluation

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

		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 (true) {
			a = getInt("  a: ");
			b = getInt("  b: ");

			// OpException must be caught or declared to be thrown	
			try {
				operationEvaluation(op, a, b);
			} // try

            catch (OpException e) {
                System.out.println(e.getMessage());
                
            } catch (DivideByZeroException e) {
				System.out.println(
					"operation skipped, because division by zero not defined");
				// System.out.println(e.getMessage());
				
			} catch (Exception e) {
				System.out.println("operation skipped, because <I don't know>");
				
			} finally {
				// optional, generally
				// required if no catch block
			} // catch

			op = getInt("next Operation: ");
		} // while

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


} // ExceptionDemo4

//------------------------ 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

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

class OpException extends Exception {

	public OpException() {
		super("wrong operation code");
	}

} // class OpException