[Resolved] OOP is new to me...Extract Question

[Kudose]

Hello all. I am finally getting around to coding in OOP design and have a few questions. I have done a little reading on google and codewalkers and have devised a rather crappy first project.

Here I have an untested script. Here are my questions.

1. Do the variables name and grade have to be called as var $name; and var $grade; at the beginning of my class to be used in the manner I have coded below?

2. Why or why not?

3. How would I pull the data from all 3 entries?

4. Am I going about this all wrong from the beginning?

Thanks!

<?php
class Grades {
	var $name;
	var $grade;

function StudentGrades($name, $grade){
	$this->name = $name;
	$this->grade = $grade;
}

function ReportCard($name){
	return $this->name." ".$this->grade."<br />";
}
}

$myBook = new Grades;
$myBook->StudentGrades("Travis", "99%");
$myBook->StudentGrades("Kayla", "98%");
$myBook->StudentGrades("Timmy", "50%");

//um...how do I display these?
//use a foreach and then use ReportCard()?

?>

[Shrike]

Your going along the right lines. First up, you should do initialisation in the constructor. Not a rule, but a principle. Secondly, $names and $grades should be declared before use. With regard to having multiple records, perhaps the variables could be arrays, then you could store all the results in there. Not very OOP though. So perhaps you should make a class ReportCard and a class ReportCards.

class ReportCard
(
  var $name;
  var $grade;
  function reportCard($name, $grade)
  {
    $this->name = $name;
    $this->grade = $grade;
  }
}

class ReportCards
{
  var $reportcards = array();
  function addCard($reportcard)
  {
    $this->reportcards[] = $reportcard
  }
}

$r = new ReportCards;
$r->addCard(new ReportCard("Travis", "99%"));

So everything is an object, and so can be treated as such in the greater scheme of things. So now we need some display methods

class ReportCard 
{ 
  var $name; 
  var $grade; 
  function reportCard($name, $grade) 
  { 
    $this->name = $name; 
    $this->grade = $grade; 
  } 

  function display() 
  { 
    echo $this->name . ": " . $this->grade . "<br>"; 
  } 
} 

class ReportCards 
{ 
  var $reportcards = array(); 
  function addCard($reportcard) 
  { 
    $this->reportcards[] = $reportcard;
  } 

  function displayReportCards() 
  { 
    foreach($this->reportcards as $reportcard) 
    { 
      $reportcard->display(); 
    } 
  } 
} 

$r = new ReportCards; 
$r->addCard(new ReportCard("Travis", "99%")); 
$r->addCard(new ReportCard("Foobar", "0%")); 
$r->displayReportCards();

In PHP 5 you can tighten things up alot, by making use of private variables, and type hinting. But that's another story 😉

[Kudose]

I think my problem in learning OOP is that I tend to get lost in the classes and the -> things while trying to visualize the script working in my head...

That is a great example and I am sure it will help me out in understanding the basics about OOP.

Thanks.

🙂

[Kudose]

One quick question...

You called display() in the class ReportCards when display() is created in ReportCard.

I thought that methods had to be contained within thier own scope.

Unless I am off, becuase they are all public within the public scope otherwise set to private or protected?

Forgive me if I am way off...still learning.

[Kudose]

One more thing...sorry.

IN this block of code

$r = new ReportCards; 
$r->addCard(new ReportCard("Travis", "99%")); 
$r->addCard(new ReportCard("Foobar", "0%")); 
$r->displayReportCards();

I notice how you create a new ReportCard and just enter the data in the new class. Which you can do becuase the function and class name are the same. I read somewhere that PHP looks first for the function with the same name as the class to execute first.

My question is, can you modify your code above to show how to add a new ReportCard when the function name within the class is different.

i.e. Class = studentData
Function = ReportCard

Thanks.

🙂

EDIT

Using the following code, I get no output. Any guess as to why? No errors...if I uncomment the lines that are commented out, I get the expected results...

<?php
class studentData {
	var $name;
	var $grade;

function studentData($name, $grade) {
	$this->name = $name;
	$this->grade = $grade;
}

function displayGrade(){
	return $this->name.": ".$this->grade."<br />";
}
}

class reportCards {
	var $cards = array();

function addCard($AddGrade) {
	$this->cards[] = $AddGrade;
}

function showCards() {
	foreach($this->cards as $card){
		$card->displayGrade();
		//echo $card."<br />";
	}
}
}

$grade = new reportCards;
$grade->addCard(new studentData("Travis", "100%"));
$grade->addCard(new studentData("Foobar", "0%"));
$grade->showCards();
?>

Thanks!

/EDIT

[Shrike]

I assume that you know the difference between a class and an object. First of all the class reportCards is really just a container for studentData objects.

Your right in thinking that a classes methods are self contained. But when the showCards() method is called, it just iterates through the array of studentData objects, calling the displayGrade() method for each. This principle is called polymorphism, that is, different types of object can be used in the same way, provided they have a common method. In our case there is only one type of object, but you can see the benefit if you were to create a second type.

It's generally good to put initialisation routines in the constructor (the method that is 'automatically' called), and use normal methods to do operations on the data. That reduces coding effort and keeps things clean and clear for other users. It's up to you in the end though. To have a normal method which does the initialisation, you would have to first create the studentGrade object, then call the method to add the data, then add the object to the container.

Lastly you are returning the result of the displayGrade() method. So you would need to say

echo $card->displayGrade();

[Kudose]

Works now. Now that I finally got something working, maybe I can tackle bigger and more enlightening tasks.

Thanks.

🙂