I am reading this book. The author is trying to model a lesson in a college. The goal is to output the Lesson Type (Lecture or Seminar), and the Charges for the lesson depending on whether it is a hourly or fixed price lesson. So the output should be:

lesson charge 20. Charge type: hourly rate. lesson type seminar.
lesson charge 30. Charge type: fixed rate. lesson type lecture.

When the input is as follows:

$lessons[] = new Lesson('hourly rate', 4, 'seminar');
$lessons[] = new Lesson('fixed rate', null, 'lecture');

I wrote this:

class Lesson {
    private $chargeType;
    private $duration;
private $lessonType;

public function __construct($chargeType, $duration, $lessonType) {
    $this->chargeType = $chargeType;
    $this->duration = $duration;
    $this->lessonType = $lessonType;
}

public function getChargeType() {
    return $this->getChargeType;
}

public function getLessonType() {
    return $this->getLessonType;
}

public function cost() {
    if($this->chargeType == 'fixed rate') {
        return "30";
    } else {
        return $this->duration * 5;
    }
}
}

$lessons[] = new Lesson('hourly rate', 4, 'seminar');
$lessons[] = new Lesson('fixed rate', null, 'lecture');

foreach($lessons as $lesson) {
    print "lesson charge {$lesson->cost()}.";
    print " Charge type: {$lesson->getChargeType()}.";
    print " lesson type {$lesson->getLessonType()}.";
    print "<br />";
}

But according to the book, I am wrong (I am pretty sure I am, too). The author gave a large hierarchy of classes as the solution instead. In a previous chapter, the author stated the following 'four signposts' as the time when I should consider changing my class structure:

• Code Duplication
• The Class Who Knew Too Much About His Context
• The Jack of All Trades - Classes that try to do many things
• Conditional Statements

The only problem I can see is Conditional Statements, and that too in a vague manner - so why refactor this? What problems do you think might arise in the future that I have not foreseen?