Object Oriented Programming with PHP

1. Object Oriented Programming with PHP XU Yinqing, Charles SEEM PHD YEAR 2

2. Outline(1) • What is OOP • What is an Object • What is a class • Commenting code • Inheritance (Extending a class) • Visibility (public, private, protected) • Final • Abstract Classes • Static Methods and properties • Interfaces

3. Outline(2) • PHP Class Functions • get_declared_interaces() • get_class() • class_exists() • get_declared_classes() • Autoload • Overloading • Class Constants

4. What is OOP • There is no hard and fast definition of what Object Oriented Programming (OOP) is • ObjectOriented Programming (OOP) is a programming concept that treats functions and data as objects • This tutorial we will see how data and functions can be represented as re-usable objects

5. What is an Object • An object is a bunch of variables and functions all lumped into a single entity • The object can then be called rather than calling the variables or functions themselves • Within an object there are methods and properties • The methods are functions that manipulate data within the object. • The properties are variables that hold information about the object.

6. What is a Class • A class is the blueprint for your object. • The class contains the methods and properties, or the characteristics of the object. • It defines the object. • Use a vehicle object as an example

7. Vehicle Object Example • All vehicles share similar characteristics, e.g.: number of doors, they are painted some color, they each have a price.  • All vehicles do similar things also, drive, turn left, turn right, stop etc. These can be described as functions, or in OOP parlance, methods. • So, the class holds the definition, and the object holds the value • You declare class in PHP by using the class keyword.

8. Vehicle Object Example

9. Vehicle Object Example • With this simple class definition we can now create one, or many, vehicle objects. • To create a new object from the class definition we use the new keyword

10. Commenting code

11. Inheritance (Extending a class) • the greatest feature of the PHP OOP model is Inheritance • Inheritance is the ability of php to extend classes (child classes) that inherit the characteristics of the parent class. • The resulting object of an extend class has all the characteristics of the parent class, plus whatever is in the new child, or extended class. • In this instance we will extend the vehicle class and add a motorcycle. A motorcycle is still a vehicle and shares many of the same attributes such as price, drive etc. But a motorcycle has some unique features that a car does not.

12. Inheritance

13. Inheritance • You see in the motorcycle class that we have used the keyword extends to extend our vehicle class. • We can then proceed to set vars in the both the parent class and the child class.  • The child class has inherited all the characteristics of the parent vehicle class.

14. Visibility (public, private, protected) • The visibility of class members, (properties, methods), relates to how that member may be manipulated within, or from outside the class. • Three levels of visibility exist for class members • Public • Private • Protected • Public class members (properties and methods) are available through-out the script and may be accessed from outside the class • By default, all class members are public.

15. Public

16. Protected • private methods and properties in a parent class are not visible to child classes and cannot be accessed. • To access a parent method or property from a child class you need to use the protected keyword. • Like the private keyword, protected methods and properties are available only to the class that created them. • But unlike private, protected methods and properties are visible from a parent class.

17. Private • Having our properties (variables) visible, or accessible from any part of our script can work against us. • A could arise if we lost track of our values and changed the value of $num.

18. Final • As we saw in the previous section there are ways to protect your code from being used in an improper manner. • Another way of protecting yourself is the Finalkeyword. • Any method or class that is declared as Final cannot be overridden or inherited by another class. ERROR!

19. Abstract Classes • An abstract class is a class that cannot be instantiated on its own. • You cannot create a new object from it. ERROR!

20. Abstract class • You can inherit from an abstract class • Any class that extends an abstract parent class must create an interface of the parent abstract methods. If this is not done a fatal error is generated.

21. Static Methods and Properties • The use of the static keyword allows class members (methods and properties) to be used without needing to instantiate a new instance of the class. • The static declaration must come after the visibility declaration, eg:public static myClass{ • Because there is no object created when using a static call, the keyword $this and the arrow operator, -> are not available. • Static variables belong to the class itself and not to any object of that class. • To access within the class itself you need to use the self keyword along with the :: scope resolution operator.

22. Static Methods and Properties • The above snippet will echo Bar

23. Static Methods and Properties • Static properties are often used as counters. Here we will use a basic counter class.

24. Interfaces • Interfaces in PHP allow you to define a common structure for your classes. • An interface cannot be instantiated on its own.  • One of the goals of OOP is re-use of code. • The interface methods have no internal logic, they are simply a "mapping" or constraint of what the class, or classes, should implement.

25. PHP Class functions • PHP has available several class functions to help you through the OOP mine field • get_declared_interfaces() • class_exists() • get_class() • get_declared_classes() • Each of these is shown here beginning with the get_declared_interfaces().

26. get_declared_interfaces() • This helper function provides an array of all the available declared interfaces.

27. Other functions $foo is from the fax class 1 0 -> stdClass 1 -> Exception 2->… 3->… … 106 -> fax 107 -> printer

28. Autoload • The class definition must be included in every call to an object • This is commonly achieved with the include() or require() functions such as below

29. Autoload • The solution to this sort of mess is __autoload() • The __autoload() function will internally search out the class and load its definition.

30. Overloading • Overloading in PHP has caused much confusion for no real reason • PHP Overloading can be broken down into two basic components • Method overloading • Property overloading • Method Overloading is achieved by a special function named __call() • It is available as a sort of method wildcard for calls to undefined methods within a class. This special function is only called when the original method name does not exist. • The __call() will only work when the class method you are trying to access does not exist

31. Overloading:_call() • Of course the above snippet of code will produce an error such asFatal error: Call to undefined method my_class::bar() in /www/overload.php on line 12. because we have called the bar() class method that does not exist. • Enter __call(). With the __call() function in place, PHP will try to create the function and you have any code within the _call() method that you like.  • The __call() method takes two arguments, the method name, and the arguments. • Your call to the undefined method may have many arguments and these are returned in an array.

32. Overloading:_call() • The above code will print the followingbarArray ( [0] => arg1 [1] => arg2 ) • The __call() method has returned the method name that we called along with the array of args passed to it.

33. Overloading • The second part of overloading refers to properties and the ability to be able to dynamically get and set object properties. • The __get() function is called when reading the value of an undefined property, and __set() is called when trying to change that properties value.

34. Overloading:_set() • The result from above will be:The value of bar is Blue Smarties • We have described a class named candy which contains a public property named $type •  It has a simple method and our __set() method. After the class our user code creates a new instance of the candy class. • Then we try to set a variable that does not exist in the class. Here the __set method takes control and assigns it for us. We then see in our __set method that it echoes the name of the variable, plus its intended value. The __set() method takes two arguments, the name of the non-existantvariable, and its intended value.

35. Overloading:_get() • From the above code we get the resultRetrieving element of $choctype property with index of milkThe value of the following element property is 0

36. Class Constants • You have more than likely seen the use standard constants in PHP. To define a standard constant we use this code:

37. Class Constants • To define a class constant we use the const keyword.

38. Class Constants • Each of the above methods would output the same lineAn Error has occurred!

39. End • Thank you!