[PHP] Inheritance problem

[Bernard Chamberland]

Hi,

I would like to post the following question related to an inheritance 
problem with PHP OO programming : 

With an object of a subclass, I call a method of the parentclass in order 
to modify an attribute of the parentclass. It does work correctly but later 
when I call the display method of the parentclass, I receive the previous 
value of the attribute !!!

The code below shows the problem :
The parentclass is "Ressource"
The subclass is "Water"
The attribute of the parentclass is "$volume"
The method to update $volume is "increase"
The method to display the parentclass is "display"

An explanation and a trick to fix the problem would be greatly appreciated.

Thanks !

Bernard


<?php

    define('_MAXX', 10);
    define('_MAXY', 10);
    define('_MAXENERGY', 20);
    define('_MAXRESERVEWATER', 20);
    define('_MAXVOLUMEWATER', 10);
    define('_MAXVOLUMEPLANT', 10);

class Jungle
{
    var $jungleobjects; // composition relation = array of $Jungleobject

    function Jungle()
    {
        // Create eaux
        for ($i=1; $i<=2; $i++) { //>
            $this->jungleobjects[] = new Water($posx = mt_rand(1, _MAXX),
                                               $posy = mt_rand(1, _MAXY),
                                               $volume = mt_rand(1, 
_MAXVOLUMEWATER));
        }
        // Create plantes
        for ($i=1; $i<=1; $i++) { //>
            $this->jungleobjects[] = new Plant($posx = mt_rand(1, _MAXX),
                                               $posy = mt_rand(1, _MAXY),
                                               $volume = mt_rand(1, 
_MAXVOLUMEPLANT));
        }

    }

    function display()
    {
        foreach ($this->jungleobjects as $jungleobject) {
            $jungleobject->display();
        }
    }

    function receiverain($density)
    {
        foreach ($this->jungleobjects as $jungleobject) {
            $jungleobject->receiverain($density);
        }
    }


} // Jungle

class Jungleobject
{
    var $posx;
    var $posy;

    function Jungleobject($posx, $posy)
    {
        $this->posx = $posx;
        $this->posy = $posy;
    }

    function display()
    {
        echo "<br>";
        echo "Class : ".get_class($this)."<br>";
        echo "Posx : ".$this->posx."<br>";
        echo "Posy : ".$this->posy."<br>";
    }

    function receiverain($density) // Abstract method : should be defined 
at sub-class level (not mandatory)
    {
        echo "Class : ".get_class($this)." Nothing to do with rain"."<br>";
    }

    function evoluer() {} // Abstract method : should be defined at 
sub-class level (not mandatory)

} // Jungleobject

class Ressource extends Jungleobject
{
    var $volume;

    function Ressource($posx, $posy, $size)
    {
        $this->Jungleobject($posx, $posy);
        $this->volume = $size;
    }

    function increase($quantity)
    {
        echo "Class : ".get_class($this)." method : increase 
($quantity)"."<br>";
        echo "Actual volume : $this->volume"."<br>";
        $this->volume += $quantity;
        echo "New volume : $this->volume"."<br>";
    }

    function display()
    {
        jungleobject::display();
        echo "Volume (Ressource) : $this->volume"."<br>";
    }

} // Ressource

class Plant extends Ressource
{
    function Plant($posx, $posy, $volume)
    {
        //$this->Ressource($posx, $posy, $volume);
        Ressource::Ressource($posx, $posy, $volume);
    }

} // Plant

class Water extends Ressource
{
    function Water($posx, $posy, $volume)
    {
        $this->Ressource($posx, $posy, $volume);
    }

    function receiverain($density)
    {
        echo "<br>";
        echo "Class : ".get_class($this)." Welcome the rain ($density) 
!"."<br>";
        $this->increase($density);
        //Ressource::increase($density);
    }

} // Water


class Rain
{
    var $jungle;

    function Rain($jungle)
    {
        $this->jungle = $jungle;
    }

    function fall($density)
    {
        $this->jungle->receiverain($density);
    }


} // Rain

// Main

$myjungle = new Jungle();
$myrain = new Rain($myjungle);

$myjungle->display();
$myrain->fall(10);
$myjungle->display();


?>




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