8. Object Oriented Programming with PHP - PHP & MySQL Web Development


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Basic concepts about Object Oreinted Programming with PHP
Telerik Software Academy: http://academy.telerik.com/school-academy/meetings/details/2011/10/11/php-school-academy-meeting
The website and all video materials are in Bulgarian.

This lecture discusses the following topics:

Classes and objects
Methods and properties
Static methods and properties
Abstraction and interfaces
Object Iteration
Object Cloning
Autoloading Classes

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8. Object Oriented Programming with PHP - PHP & MySQL Web Development

  1. 1. Object-Oriented Programming with PHP Methods, Classes, Objects, AbstractionNikolay KostovTechnical Trainerhttp://nikolay.itTelerik Software Academyacademy.telerik.com
  2. 2. Summary Classes and objects Methods and properties Scope Inheritance Static methods and properties Constants Abstraction and interfaces
  3. 3. Summary (2) Overloading Object Iteration Object Cloning Serialization Namespaces Autoloading Classes
  4. 4. Classes and Objects The idea of Object Oriented Programming is to move the architecture of an application closer to real world  Classes are types of entities  Objects are single units of a given class  Example – Dog is a class, your dog Lassie is an object of class Dog  Classes have methods and properties  Classes and objects help to create well- structured application
  5. 5. Classes in PHP Declaring of a class in PHP can be done anywhere in the code class Dog { … // declare methods and properties }  Two special methods: constructor and destructor  Executed when creating or destroying new object of this class  Used to initialize or cleanup properties and etc.
  6. 6. Classes in PHP Classdefinition begins with the class keyword, followed by its name and methods and properties list name class name Method and body class A { function foo () { echo Createhere!"; "foo new object } of class A } $myFirstObject = new A(); $myFirstObject->foo(); // prints out "foo here!"; Execute method of this object  Objects of class (instances) are created with the keyword new
  7. 7. Constructors Each class can have only one constructorclass A { function __construct ($bar) { echo $bar; } function foo () { echo "foo here!"; }}$myFirstObject = new A(test);// print test  All parameters of the creating of the object are passed to the constructor
  8. 8. Properties Class can have unlimited number of properties class A { var $bar; function __construct ($bar) { $this->bar = $bar; } function myPrint () { echo $this->bar; } } $myFirstObject = new A(test); $myFirstObject->myPrint(); The $this variable points to the current object – called execution context
  9. 9. More Properties Class can specify default value for a property class A { var $bar = default value; … Properties can be accessed from the outside world class A { var $bar = default value; … } $obj = new A; echo $obj->bar;
  10. 10. $this Example of what $this is class A { var $bar; function __construct ($bar) { $this->bar = $bar; } function myPrint () { echo $this->bar; } } $myFirstObject = new A(test); $myFirstObject->myPrint(); // prints test $anotherObject = new A(foo); $anotherObject ->myPrint(); // prints foo; Can be used to access methods too
  11. 11. Destructors Each class can have only one destructor  Must be public class A { function __construct ($name) { $this->fp = fopen ($name, r); } function __destruct () { fclose($this->fp); } } $myFirstObject = new A(test);  Destructors are automatically called when script is shutting down
  12. 12. Scope Each method and property has a scope  It defines who can access it  Three levels – public, protected, private  Private can be access only by the object itself  Protected can be accessed by descendant classes (see inheritance)  Public can be accessed from the outside world  Level is added before function keyword or instead of var  var is old style (PHP 4) equivalent to public  Constructors always need to be public
  13. 13. Scope Exampleclass A { private $bar; public function __construct ($bar) { $this->bar = $bar; } public The $bar variable is private so function myPrint () { echo $this->bar; only the object can access it } The myPrint method is} public, so everyone can call it$myFirstObject = new A(test);$myFirstObject->myPrint(); // prints test// this will not work:echo $myFirstObject->bar;
  14. 14. Inheritance A class can inherit (extend) another class  It inherits all its methods and properties class A { public $bar = test; public function example () { … } } class B extends A { … } $obj = new B(); echo $obj->bar; //prints test //calls the A-class function $obj->example();
  15. 15. Protected Scope Method or property, declared as protected can be accessed in classes that inherit it, but cannot be accessed from the outside world class A { protected $bar = test; } class B extends A { public function foo () { // this is allowed $this->bar = I see it; } } $obj = new B(); echo $obj->bar; //not allowed
  16. 16. Overriding When a class inherits another, it can declare methods that override parent class methods  Method names are the same  Parameters may differ class A { public foo() { … } } class B extends A { public foo() { … } }
  17. 17. Overriding Exampleclass A { public foo() { echo called from A; }}class B extends A { public foo() { echo called from B; }}$obj1 = new A();$obj2 = new B();$obj1->foo(); // executes As methods$obj2->foo(); // executes Bs methods
  18. 18. Accessing Parent Class As -> is used to access objects methods and properties, the :: (double colon) is used to change scope  Scope Resolution Operator parent:: can be used to access parents class overridden methods  Example: call parents constructor in the child one
  19. 19. Accessing Parent Class Example of calling parent constructor class A { protected $variable; public __construct() { $this->variable = test; } } class B extends A { public __construct() { parent::__construct(); echo $this->variable; } } $obj1 = new B(); // prints test;
  20. 20. The static Keyword Defining method or property as static makes them accessible without needing an instantiation of a class  Accessed with the double-colon (::) operator instead of the member (->) operator  $this is not available in static methods  Static properties and methods can also have scope defined – public, private or protected
  21. 21. The static Keyword Example of static method and property class A { public static $myVariable; public static function myPrint() { echo self::$myVariable; } } A::$myVariable = test; A::myPrint();  Class can access statics with the self keyword  Outside world accesses statics with the class name
  22. 22. Class Constants Constants in PHP usually are declared with the define function Constants can be defined in class  Differ from normal variables – no need for $ symbol to declare and access  Declared with the const keyword  Value must be supplied with the declaration  Accessed with scope operator (::)  Can be overridden by child classes  Value must be constant expression, not a variable, class member, result of operation or function call
  23. 23. Class Constants Example of a class constant class A { const myConstant = value; public function showConstant() { echo self::myConstant; } } echo A::myConstant; $obj = new A(); $obj->showConstant();
  24. 24. Abstraction Classes, defined as abstract, cannot have instances (cannot create object of this class)  Abstract class must have at least one abstract method  Abstract methods do not have implementation (body) in the class  Only signature  The class must be inherited  The child class must implement all abstract methods  Cannot increase visibility
  25. 25. Abstraction Exampleabstract class AbstractClass { abstract protected function getValue(); abstract public functiongetValue2($prefix); public function printOut () { echo $this->getValue(); }}class Class1 extends AbstractClass { protected function getValue (){ return "Class1"; } public function getValue2($prefix) { return $prefix."NAC1"; }}
  26. 26. Abstraction Example (2)// continue from previous slideclass Class2 extends AbstractClass { protected function getValue (){ return "Class2"; } public function getValue2($prefix) { return $prefix."NAC2"; }}$class1 = new Class1();$class1->printOut(); // "Class1";echo $class1->getValue2(FOO); // FOONAC1$class2 = new Class2();$class2->printOut(); // "Class2";echo $class2->getValue2(FOO); //FOONAC2
  27. 27. Interfaces Object interfaces allow you to specify what methods a child class must implement  Declared with the interface keyword  Similar to abstract class  Interface can have only public methods  No method in interface can have implementation Interfaces are inherited with the implements keyword (instead of extends)  One class may implement multiple interfaces, if they do not have methods with same names
  28. 28. Interface Exampleinterface iTemplate { public function set ($name, $value); public function getHTML($template);}class Template implements iTemplate { private $vars = array(); public function set ($name, $value) { $this->vars[$name] = $value; } public function getHTML($template) { foreach($this->vars as $name=>$value) { $template = str_replace( {.$name.}, $value, $template); } return $template; }}
  29. 29. Overloading Overloading in PHP provides the means to dynamically create members and methods via set of "magical" methods  Invoked with interacting with members or methods that have not been declared or are not visible in the current scope  All of the magic methods must be declared as public  None of the magic functions can be called with arguments, passed by reference
  30. 30. Overloading Methods All overloading methods are invoked when accessing variable or method that is not declared or is inaccessible __set($name, $value) – when writing __get ($name) –when reading __isset ($name) – when calling isset() function __unset ($name) – when calling unset() function
  31. 31. Overloading Methods __call ($name, $arguments) - when calling a method __callStatic ($name, $arguments) – when calling a method in a static context  Added after PHP 5.3  Must always be declared as static PHP "overloading" is a lot different from most languages "overloading"  Usually it means the ability to declare two methods with different sets of parameters but same names
  32. 32. Object Iteration PHP provides a way for object to be iterated trough as a list of items (array)  foreach can be used  By default iterates all visible properties
  33. 33. Object Iteration – Exampleclass A { public $var1 = 1; public $var2 = 2; protected $var3 = 3; private $var4 = 4; function printIteration () { foreach ($this as $key=>$val) echo "$key : $valn"; }}$obj = new A();// this prints only the public propertiesforeach ($obj as $key=>$val) echo "$key : $val n";// this prints protected and private too$obj->printIteration ();
  34. 34. Object Iteration To take object iteration a step further, you can implement one of the PHP interfaces  Provided by the Standard PHP Library  Allows the objects to decide what to show and what not  Some provided interfaces:  Iterator – very long to implement but provides dull features  IteratorAggregate – simple version of Iterator interface  ArrayIterator, DirectoryIterator, etc.
  35. 35. Object Cloning An object can be cloned with the clone keyword $obj1 = new A(); $obj2 = clone $obj1;  This will create new independent object Creating a copy of an object with fully replicated properties is not always the wanted behavior
  36. 36. Object Cloning A class can implement the magic method __clone which is called for the newly created object Called "clone constructor" Allows necessary changes to be done on the newly created object Example: Object holding reference to resource – the new object must have new references, instead of copies Example: Object holding reference to another object that must not be copied
  37. 37. Object Cloning Exampleclass A { private $fileName; private $fp = null; public function open ($file) { $this->fileName = $file; $this->fp = fopen ($file, r); } public function close () { if ($this->fp) { fclose($this->fp); $this->fp = null; } } public function __clone () { // reopen the file for the new object if ($this->fp) $this->fp= fopen($this->file, r); }}
  38. 38. Serializing Objects Serializing is the process of transforming an object into a string, that can be stored  This string can be used to restore the object  Useful for storing objects in session data  Saves only properties values and class names – no methods  PHP provides the serialize and unserialize functions
  39. 39. Serializing Objects serialize ($object) – returns string, representing the object unserialize ($string) – returns new object, that is restored from the serialized string unserialize requires the class to be defined before calling it
  40. 40. Serializing Object – Exampleclass A { public $var; public function myPrint () { echo $this->var; }}$obj = new A;$obj->var = 10;$data = serialize ($obj);// store $data in a filefile_put_contents (data.dat, $data);// …// in a new page:$data = file_get_contents (data.dat);$obj = unserialize ($data);$obj->myPrint (); // prints 10
  41. 41. Serializing Methods Before serializing and after unserializing PHP checks if the class has the magic methods __sleep and __wakeup  __sleep allows the class to commit pending data, cleanup or define what needs to be stored if the object is very large  Should return array with names of properties to be stored  __wakeup allows the class to restore connections or other re-initialization
  42. 42. __sleep and __wakeupclass Connection { protected $link; private $server, $user, $pass, $db; public function __construct($server, $user,$pass, $db) { $this->server = $server; $this->user = $user; $this->pass = $pass; $this->db = $db; $this->connect(); } private function connect () { $this->link = mysql_connect ( $this->server, $this->user, $this->pass); mysql_select_db($this->db, $this->link); } // continues on next slide
  43. 43. __sleep and __wakeup // continues from previous slide public function __sleep () { // skip serializing $link return array (server, user, pass, db); } public function __wakeup () { $this->connect(); }}
  44. 44. Namespaces Namespaces in PHP are designed to resolve scope problems in large PHP libraries  Simplify development in object oriented environment  Clears the code – no long classes names In PHP all classes declarations are global  Namespaces allow to have two classes with same name  Old approach was adding prefixes to class names (Like the mysql_* functions) Available since PHP 5.3
  45. 45. Namespace Definition Namespaces are declared with the namespace keyword  Should be always in the beginning of the file <? namespace Project; class MyTemplate { … } function print_headers () { … } … ?>  Namespace can contain classes, constants, functions but no free code
  46. 46. Namespaces Classes, function and etc. in a namespace are automatically prefixed with the name of the namespace  So in the example we would use Project::MyTemplate to access the class  Constants in namespaces are defined with const keyword, not with define
  47. 47. Namespaces – Example// file Project.phpnamespace Project;// declare base classes and etc.…// file project/db.php;namespace Project::DB;// declare DB interface for work with database…// file project/db/mysql.phpnamespace Project::DB::MySQL;// implement the DB interface for mysql…// file project/db/oracle.phpNamespace Project::DB::Oracle;// implement the DB interface for Oracle…// somewhere in the projectrequire "project/db/mysql.php";$a = new Project::DB::MySQL::Connection();Project::DB::MySQL::connect();
  48. 48. Using Namespaces The use operator allows aliasing namespaces names use Project::DB::MySQL as DBLink; $x = new DBLink::Connection(); DBLink::connect();  If new name is not specified the namespace is imported in the current context (global namespace) use Project::DB::MySQL; $x = new MySQL::Connection(); MySQL::connect(); Even if aliased, every class and function can be accessed at any time by full name
  49. 49. Global Namespace By default PHP works in the global namespace  All the project is executed there  Method from the global namespace can be referred to with empty scope operator namespace Project::Files; // this is the Project::Files::fopen function function fopen (…) { … $f = ::fopen (…); // calls global fopen … }
  50. 50. Autoloading Classes Usually every class is declared in separate file  In big object oriented projects on every page you may have to include dozens of files  You can define __autoload function that is called when trying to access class that is not defined  It can include the necessary file for the class
  51. 51. Autoload Example <? function __autoload ($class_name) { $name = "includes/".$class_name.".inc.php"; if (file_exists ($name)) include $name; else echo Class not found; } ?> Exceptions, thrown in __autoload cannot be caught and result in fatal error
  52. 52. Limitation of self:: Example: class A { public static function whoami () { echo __CLASS__; } public static function test () { self::whoami(); } } class B extends A { public static function whoami () { echo __CLASS__; } } B::test(); // outputs A ?!
  53. 53. Late Static Binding PHP 5.3 introduces the late static binding which allows to reference the called class in context of static  In practice – this adds static:: scope  So if in the above example we use static::whoami() in the test() method body we get output B
  54. 54. Object-Oriented Programming with PHP курсове и уроци по програмиране, уеб дизайн – безплатно BG Coder - онлайн състезателна система - online judge курсове и уроци по програмиране – Телерик академия форум програмиране, форум уеб дизайн уроци по програмиране и уеб дизайн за ученици ASP.NET курс - уеб програмиране, бази данни, C#, .NET, ASP.NET http://academy.telerik.com програмиране за деца – безплатни курсове и уроци ASP.NET MVC курс – HTML, SQL, C#, .NET, ASP.NET MVC безплатен SEO курс - оптимизация за търсачки алго академия – състезателно програмиране, състезаниякурсове и уроци по програмиране, книги – безплатно от Наков курс мобилни приложения с iPhone, Android, WP7, PhoneGap уроци по уеб дизайн, HTML, CSS, JavaScript, Photoshop Дончо Минков - сайт за програмиране free C# book, безплатна книга C#, книга Java, книга C# Николай Костов - блог за програмиране безплатен курс "Качествен програмен код" безплатен курс "Разработка на софтуер в cloud среда" C# курс, програмиране, безплатно
  55. 55. Exercises1. Define class Student that holds information about students: full name, course, specialty, university, email, phone.2. Define constructor for the class Student that takes full name as parameter.3. Add a method in the class Student for displaying all information about the student.4. Create two students and print their information.5. Create an interface IAnimal that represents an animal from the real world. Define the method talk() that prints the specific scream of the animal ("jaff" for dogs, "muaw" for cats, etc.).
  56. 56. Exercises (2)6. Create an abstract class Cat that has Name and implements the interface IAnimal and introduces abstract method printInfo().7. Inherit from the base abstract class Cat and create subclasses Kitten and Tomcat. These classes should fully implement the IAnimal interface and define an implementation for the abstract methods from the class Cat.8. Create class Dog that implements IAnimal.9. Write a class TestAnimals that creates an array of animals: Tomcat, Kitten, Dog and calls their methods through IAnimal interface to ensure the classes are implemented correctly.
  57. 57. Exercises (3)10. We are given a school. In the school there are classes of students. Each class has a set of teachers. Each teacher teaches a set of disciplines. Students have name and unique class number. Classes have unique text identifier. Teachers have name and title. Disciplines have name, number of lectures and number of exercises. Define classes for the school (School, Class, Student, Teacher, Discipline). Keep the member fields private. Add constructors and accessor methods. Write a testing class to construct and print a sample school.
  58. 58. Exercises (4)11. We need to implement a message board where visitor can read all messages, add new messages, edit and delete existing messages. Implement this as a PHP application by following the steps below:  Create a MySQL database Messages and define in it a table messages(id, author, subject, msgDate, msgBody).  Write a class Message which will hold a single message with its id, author, subject, msgDate and msgBody. Put this class in the file message.class.php.
  59. 59. Exercises (5) Write a class DBUtils which will be responsible for database access for the entire application. Put this class in the file db-utils.class.php. Implement the following methods:  dbConnect() – connects to the MySQL database and selects Messages database  getAllMessages() – returns an array of Message objects containing all messages from the database  addMessage($msg) – inserts a message given as Message object to the database  updateMessage($msg) – updates a message given as Message object in the database  deleteMessageById($msg_id)- deletes given message specified by its primary key
  60. 60. Exercises (6) Write a PHP script index.php which displays all messages in a table. Implement a form for adding a message as separate script add-message.php. Implement deleting of a message by clicking a hyperlink in the corresponding row in the table. Implement it as separate script delete.php. Implement editing of a message by clicking on a hyperlink in the corresponding row in a table. Implement it as separate script edit-message.php.
  61. 61. Free Trainings @ Telerik Academy “PHP & MySQL Web Design" course academy.telerik.com/.../php-school- academy-meeting Telerik Software Academy  academy.telerik.com Telerik Academy @ Facebook  facebook.com/TelerikAcademy Telerik Software Academy Forums  forums.academy.telerik.com