Tutorial 4 : implementing an Abstract Class

   In this way you can define a set of object that must all follow the same format,and therefore be inter-operable. Any number of classes can extend the original. The only requirements are that each child class must declare all abstract functions,and that they must declared at the same (or a less restrictive) visibility level. Beyond that,the new class may define as many other methods and properties as you want.

Saved as testing.php

<?php

//Define an abstract class for animals

abstract class animal{

//Declare variables(properties)

public $name;

//Make a constructor to be shared that requires a name

public function __construct($namesake){

$this->name=$namesake;

}

//Declare abstract methods that each animal must implement.

abstract public function makeSound();

abstract public function eat($what);

}

//Define a cat class

class cat extends animal{

public function makeSound(){

echo "Meow\n";

}

public function eat($what){

switch ($what){

case 'kibble':

case 'cat food':

case 'mouse':

case 'bird':

echo "The cat says yum!\n";

break;

case 'grass':

case 'tinsel':

case 'hair':

echo "The cat purrs contentedly.\n";

break;

default:

echo "The cat Raises its head haughtily and walks off .\n";

}

}

}

//Define a cow class

class cow extends animal{

public function makeSound(){

echo"Moooooo!\n";

}

public function eat($what){

switch($what){

case 'grass':

case'hay':

case 'salt':

echo "The cow chews its cud.\n";

break;

default:

echo "The cow walks off ignoring it.\n";

}

}

}

//Declare a cat & a cow.

$my_cat=new cat('Mimi-ow');

$my_cow=new cow('Getrude');

echo'<pre>';

//The cat says:Meow

$my_cat->makeSound();

//The cow says:Moo

$my_cow->makeSound();

//What do they each do when they eat grass?

$my_cat->eat('grass');

$my_cow->eat('grass');

echo '</pre>';

?>

output:

Meow
Moooooo!
The cat purrs contentedly.
The cow chews its cud.

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