Why is my class worse than the hierarchy of classes in the book (beginner OOP)?
- by aditya menon
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?
