Extended classes and undefined Variables - PHP [duplicate] - php

Question

This question already has answers here:
PHP - Private class variables giving error: undefined variable
(4 answers)
Closed 4 years ago.
Square and Rectangle are classes that extends abstract class ShapesClass, defining their own Area methods.
abstract class ShapesClass
{
// Force Extending class to define this method
abstract public function Area();
}
class Square extends ShapesClass
{
private $side = 0;
function __construct($n)
{
$side = $n;
}
function Area()
{
echo $side * $side;
}
}
class Rectangle extends ShapesClass
{
var $length = 0;
var $width = 0;
function __construct($a,$b)
{
$length = $a;
$width = $b;
}
function Area()
{
echo $length * $width;
}
}
$listShapes = array();
$listShapes[0] = new Square(3);
$listShapes[1] = new Rectangle(3,4);
$listShapes[0]->Area();
$listShapes[1]->Area();
I get undefined variable errors on side, length and width.
Doesn't these three variables have default values and are also set by the constructor.

Answer 1

You actually want to refer to them as $this->foo
function __construct($a,$b)
{
$this->length = $a;
$this->width = $b;
}
Basically $foo acts like a local, variable, scoped to current method. $this->foo acts like a instance variable, which is available anywhere in the class.

Answer 2

In your code whenever we create variables for any class we can call them inside methods with the class reference only i.e. $this
Also, in php we can define the variables with var there are public, protected and private keywords to define any variable.
So, you can update your code with the below code
abstract class ShapesClass
{
// Force Extending class to define this method
abstract public function Area();
}
class Square extends ShapesClass
{
private $side = 0;
function __construct($n)
{
$this->side = $n;
}
function Area()
{
echo $this->side * $this->side;
}
}
class Rectangle extends ShapesClass {
private $length = 0;
private $width = 0;
function __construct($a,$b)
{
$this->length = $a;
$this->width = $b;
}
function Area()
{
echo $this->length * $this->width;
}
}
$listShapes = array();
$listShapes[0] = new Square(3);
$listShapes[1] = new Rectangle(3,4);
$listShapes[0]->Area();
$listShapes[1]->Area();