problem with OOP

[drtanz]

Hi I am trying out some object oriented programming but I am stuck on the following problem. As you can see from the code below I have two classes, Bear and PolarBear, which inherits from Bear. Now when I create a new instance of PolarBear I am getting the food and color attributes of Bear in this instance instead of those defined in PolarBear. What am i doing wrong? thanks

 

Hi, my name is Nikolai and I weigh 235 kgs

Nikolai eats honey

Nikolai is brown

Hi, my name is Jon and I weigh 300 kgs

Jon eats honey

Jon is brown

Hi, my name is Maria and I weigh 100 kgs

Maria eats honey

Maria is brown

Hi, my name is Banavage and I weigh 500 kgs

Banavage eats honey

Banavage is brown

 

 

index.php

 

<?php

include 'bear.cls.php';

include 'polarBear.cls.php';

$nikolai = new Bear('Nikolai',235);

  $jon = new Bear('Jon',300);

$maria = new Bear('Maria',100);

$banavage = new PolarBear('Banavage',500);

?>

 

 

polarBear.cls.php

 

<?php

 

class PolarBear extends Bear {

 

public function PolarBear($bearName,$bearWeight) {

parent::Bear($bearName,$bearWeight);

$this->color = 'white';

$this->food = 'fish';

$this->name = $bearName;

// $this->Eat();

//$this->Color();

}

 

/* public function Eat() {

echo $this->name." eats ".$this->food."<br />";

}

 

public function Color() {

echo $this->name." is ".$this->color."<br />";

}

*/

 

}

 

bear.cls.php

 

<?php

 

class Bear {

public $name;

public $weight;

public $age;

public $color;

public $food;

 

public function Bear($bearName,$bearWeight) {

//echo "Hi, my name is ".$name." and I weigh ".$weight." kgs<br />";

$this->name = $bearName;

$this->weight = $bearWeight;

$this->color = 'brown';

$this->food = 'honey';

$this->NameWeight();

$this->Eat();

$this->Color();

}

 

public function Eat() {

echo $this->name." eats ".$this->food."<br />";

}

 

public function Color() {

echo $this->name." is ".$this->color."<br />";

}

 

public function NameWeight() {

echo "Hi, my name is ".$this->name." and I weigh ".$this->weight." kgs<br />";

}

 

}

 

?>

[Aeglos]

You are calling the eat() and color() methods in the Bear constuctor, while those in PolarBear are commented out. Therefore the PolarBear is always Brown and eats Honey since it hasn't set it's color to white or it's food to fish before it's parent's constructor is called. Uncomment the calls in PolarBear and you should see something like:

 

Hi, my name is Banavage and I weigh 500 kgs

Banavage eats honey

Banavage is brown

Banavage eats fish

Banavage is white

[drtanz]

yeah thats also a problem because i want to eliminate the

 

Banavage eats honey

Banavage is brown

 

lines as they belong to Bear while Banavage is a PolarBear

[Aeglos]

Well, remove those calls from the constructor then

 

It's cleaner to do something like:

 

$nikolai = new Bear('Nikolai',235);
$jon = new Bear('Jon',300);
$maria = new Bear('Maria',100);
$banavage = new PolarBear('Banavage',500);

$nikolai->info();
$jon->info();
$maria->info();
$banavage->info();

 

where the info() method is like:

public function info()
{
    $this->NameWeight();
    $this->Eat();
    $this->Color();
}

 

And as a side note, this belongs in the OOP subforum

[drtanz]

hi sorry for posting here missed the other forum, i can see that this is a cleaner way, im just struggling to understand why this way it works and when they were called from the constructor it didnt work, i might be overseeing something obvious but i cant figure it out yet...

[Aeglos]

Just remember that everything inside functions or objects happens sequentially, one thing after the other.

 

The PolarBear constructor goes like this (with the calls uncommented):

 

public function PolarBear($bearName,$bearWeight) 
{
     parent::Bear($bearName,$bearWeight);
     $this->color = 'white';
     $this->food = 'fish';
     $this->name = $bearName;
     $this->Eat();
     $this->Color();
}

 

Notice that BEFORE setting the color to white and food to fish you are calling the parent's (Bear) constructor. So let's do a simple replace to get the equivalent code and see what is going on:

 

public function PolarBear($bearName,$bearWeight) 
{
     /* Begin parent's constructor */
     $this->name = $bearName;
     $this->weight = $bearWeight;
     $this->color = 'brown';
     $this->food = 'honey';
     $this->NameWeight();
     $this->Eat();       //Outputs: Honey
     $this->Color();     //Outputs: Brown
     /* End parent's constructor */

     $this->color = 'white';
     $this->food = 'fish';
     $this->name = $bearName;
     $this->Eat();       //Outputs: Fish
     $this->Color();     //Outputs: White
}

 

You see now? The Bear constructor calls the Eat() and Color() Methods before the PolarBear different properties are defined, thus it can only read the ones that the parent Bear class has set. You can also see that you are setting the same name twice... not really important though.

 

Hope that clears it up some more. Cheers!

[drtanz]

Right thats a great explanation i see what is happenning now, I was just thinking there was some other way of doing it the way I was doing it in the beginning, without having to use the info() function and in some way overriding the Bear's eat and color functions but it seems that wasnt possible. thanks