### oefneing 4 ###

public void onClick(View v) {
    try {

        num1 = Double.parseDouble(firstNumber.getText().toString());
        num2 = Double.parseDouble(secondNumber.getText().toString());
        div = num1 / num2;

        if (num2 == 0) {
            throw new ArithmeticException();
        } else {
            addResult.setText(Double.toString(div));
        }

    } catch (Exception e) {
        if (e instanceof NumberFormatException) {
            addResult.setText("Geen tekst a.u.b.");
        } else if (e instanceof ArithmeticException){
            addResult.setText("Delen door 0 niet toegestaan!");
        } else {
            addResult.setText(e.getMessage());
        }
    }
}