@Override
    protected List<String> getValidationErrors() {
        final List<String> errors = super.getValidationErrors();
        if (!ValidationHelper.isPositiveInteger(widthTextField.getText()))
            errors.add("Width should be positive integer number");
        if (!ValidationHelper.isPositiveInteger(heightTextField.getText()))
            errors.add("Height should be positive integer number");
        return errors;
    }