Object Oriented Programming in PHP5

An overview of some of the basics for developing object oriented code in PHP5.

Transcript

1. OBJECT ORIENTED PROGRAMMING IN PHP 5 Introduction to Web Dev Connect | February 7th, 2012
2. Before We Get Started What is Object Oriented Programming? How Does PHP Implement these Concepts? Encapsulation Encapsulation Visibility Inheritance Polymorphism Abstraction Magic Methods Common Design Patterns
3. What is Object Oriented Programming? Objects are instances of classes. Classes define how their instances (objects) will instances (objects) will operate. Objects can contain “private” information and methods. Classes can inherit from other classes
4. Encapsulation class A { }
5. Encapsulation classA { const C = 5; var $aVariable; function __construct() function __construct() { } function __destruct() { } function doSomething() { } }
6. Visibility class A { const C = 5; protected $aVariable; public $bVariable; private $cVariable; private $cVariable; protected function __construct() { } private function __destruct() { } public function doSomething() { } }
7. Inheritance class A { const C = 5; protected $aVariable; public $bVariable; private $cVariable; protected function __construct() { } private function __destruct() { } public function doSomething() { } } class B extends A { public function doSomething() { parent::doSomething(); } }
8. Polymorphism “ “Polymorphism describes a pattern in Polymorphism describes a pattern in object oriented programming in which object oriented programming in which object oriented programming in which object oriented programming in which classes have different functionality classes have different functionality while sharing a common interface.” while sharing a common interface.”
9. Polymorphism Interfaces interface MyInterface { public function doSomething(); } // All classes implementing the “MyInterface” interface must contain a public doSomething() method classA implements MyInterface classA implements MyInterface { public function doSomething() { } } class InvalidClass implements MyInterface { protected function doSomething() { } }
10. Polymorphism Abstract Classes abstract class MyAbstractClass { abstract public function doSomething(); protected function _echo($a) { echo $a; } } // All classes extending the “MyAbstractClass” class must implement the doSomething() method classA extends MyAbstractClass { public function doSomething() { $this->_echo(“We did something.”); } }
11. Magic Methods PHP supports several “magic” methods These methods are optional PHP will look for them in your classes at key moments moments We’ll be talking about just a couple: __construct __destruct __get __set
12. Magic Methods __construct() This method will be called when an object is This method will be called when an object is first being instantiated. This is where you would commonly put all your initialization logic.
13. Magic Methods __construct() class X extends DatabaseClass { public function __construct() { { parent::_initDb(); } }
14. Magic Methods __destruct() This is the counterpoint to the __construct This is the counterpoint to the __construct method. It is called when your object is destroyed by PHP.
15. Magic Methods __destroy() class X extends DatabaseClass { public function __construct() { parent::_initDb(); parent::_initDb(); } public function __destroy() { parent::_closeDbConnection(); } }
16. Magic Methods __get() This magic method allows you to “overload” a property. By using __get() you can have your object return data when a requested property doesn’t really exist. This is can be used to simulate read-only access to public attributes.
17. Magic Methods __get() classA { protected $_vars = array(“foo” => “bar”); public function __get($name) public function __get($name) { return $this->_vars[$name]; } } $MyA = new A; echo $MyA->foo; // echos: “bar” $MyA->foo = “foobar”; // Error, property “foo” is not defined
18. Magic Methods __set() This is the counterpoint to __get() Using this method you can simulate setting an object’s public property that doesn’t really exist.
19. Magic Methods __set() class A { protected $_vars = array(“foo” => “bar”); public function __get($name) { return $this->_vars[$name]; return $this->_vars[$name]; } public function __set($name, $value) { $this->_vars[$name] = $value; } } $MyA = new A; echo $MyA->foo; // echos: “bar” $MyA->foo = “foobar”; echo $MyA->foo; // echos: “foobar”
20. Magic Methods Beware when implementing __get() and __set() methods. These methods should be used sparingly as they can make debugging a nightmare.
21. Common Design Patterns Singleton “Singleton” classes are classes that can only be instantiated once. Examples might be a database handler or a session handling class.
22. Common Design Patterns Singleton class SingletonClass { static protected $_instance; protected function __construct() { } public function getInstance() { if (self::$_instance instanceof SingletonClass){ if (self::$_instance instanceof SingletonClass){ return self::$_instance; } self::$_instance = new SingletonClass(); return self::$_instance; } } $Invalid = new SingletonClass(); // Error, cannot access the protected __construct method $Valid = SingletonClass::getInstance();
23. Common Design Patterns Factory The “Factory” design pattern allows you to easily create new instances of related classes. Examples might be a factory for different types of system users.
24. Common Design Patterns Factory classAnimal { static public function factory ($name) { $className = “Animal_” . $name; return new $className; } } } classAnimal_Cat extends Animal { } classAnimal_Dog extends Animal { } $MyDog = Animal::factory(“Dog”); $MyCat = Animal::factory(“Cat”);
25. QUESTIONS?
26. Further Reading Polymorphism http://net.tutsplus.com/tutorials/php/understanding-and-applying- polymorphism-in-php/ Magic Methods http://net.tutsplus.com/tutorials/php/deciphering-magic-methods-in-php/