Page 238 - Beginning PHP 5.3

Part II: Learning the Language
Similarly, here ’ s how you make a final method:

class ParentClass {
public $someProperty = 123;
public final function handsOffThisMethod() {
echo “A method”;
}
}

// Generates an error:
// “Cannot override final method ParentClass::handsOffThisMethod()”

class ChildClass extends ParentClass {
public function handsOffThisMethod() {
echo “Trying to override the method”;
}

}
You probably won ’ t need to create final classes or methods that often; usually it ’ s better to allow your
classes to be extended, because it makes your code more flexible.

Using Abstract Classes and Methods
Being able to create new child classes from parent classes is all very well, but things can get out of hand
if a child class has radically different functionality to its parent. Sometimes it ’ s good to be able to lay
down some ground rules about how a child class should behave. Abstract classes and methods let you
do just that.
To illustrate class abstraction, cast your mind back to the Shape class example you created earlier.
Remember that you created a generic Shape parent class that contained some basic functionality, then
extended the Shape class with the Circle and Square child classes.

Now, both Circle and Square contain a getArea() method that calculates the shape ’ s area, regardless
of the type of shape. You can use this fact to your advantage to create a generic ShapeInfo class that
contains a method, showInfo() , that displays the color and area of a given shape:
class ShapeInfo {
private $_shape;

public function setShape( $shape ) {
$this- > _shape = $shape;
}

public function showInfo( ) {
echo “ < p > The shape’s color is “ . $this- > _shape- > getColor();
echo “, and its area is “ . $this- > _shape- > getArea() .”. < /p > ”;
}

}

200

9/21/09 9:03:43 AM
c08.indd 200
c08.indd 200 9/21/09 9:03:43 AM