PACS – 10/19/131 Object-Oriented Programming “Object-oriented programming opens the door to...

PACS – 10/19/13 1

Object-Oriented Programming

“Object-oriented programming opens the door to cleaner designs, easier maintenance, and greater code reuseability.” – Opening of Chapter 6, “Programming PHP” from O’Reilly.A different way of coding. Your code won’t run faster, be more accurate, have prettier output, etc.Although the concept dates from the 1950’s, Simula from 1967 is probably the first language.

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Smalltalk from 1972 was the first OOP language in widespread use.In the mid 1990’s, OOP formed the basis for C++, Java, C#, VB.NET, Python and others.Other languages have had OOP extensions added: Visual Basic, Fortran, Perl, Cobol, etc.And PHP starting in v4. OOP support was much improved in v5.

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Non-OOP is called procedural or modular coding.First code was one big glob.Next came separation of code into functional units using subroutines or functions.OOP further separates the data and code into ‘objects’. This makes it easier to debug because only the associated code works with the data.Objects won’t touch another’s data.

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As with anything else new, OOP comes with its own terminology and we need to learn some of these terms before we can write our own code or can use someone else’s code library.A class is a template for building objects.An object is an instance or occurrence of a class.An object will have user data with attached code to work with that data.

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The data associated with an object are called its properties.The functions associated with an object are called its methods.When you define a class, you define the names of its properties and give the code for its methods.Encapsulation is the idea that a class’s methods deals with the class properties and no other method does.

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Inheritance is a way of defining a new class by extending an existing class with new or changed properties and methods.The original class is called the parent, super, or base class.

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We’ll look at some basic syntax.Create an object:

$object = new class;

Access a property:$object->propertyname

Access a method:$object->methodname([arg,…])

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Methods act just like functions, so they can take arguments and return a value.You can specify which methods and properties are publicly accessible to provide encapsulation.Declaring a class:

class classname [extends baseclass] {

[var $propertyname [ = value];]

[function methodname(args) { code }] }

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Within a method, the $this variable is a reference to the object on which the method was called.Declaring a method:

class Person {

public $name; // optional but good practice

public function get_name(){ return $this->name;}

public function set_name($new_name) { $this->name = $new_name;}

}

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Advanced – When declaring properties, you can use the following access modifiers instead of var to provide encapsulation:

public $data1 [=3]; // global

protected $data2 [=4]; // within subclasses

private $data3 [=5]; // within class

Advanced – You can also define static properties on variables on an object class. No object necessary to reference these.

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Like global constants assigned with the define() function, you can assign constants within a class:

class PaymentMethod{

Const TYPE_CREDITCARD = 0;

Const TYPE_CASH = 1; }

It’s common practice to define class constants in upper case.

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To inherit properties and methods from another class, use the extends keyword:

class Person {

public $name, $address, $age;

}

class Employee extends Person {

public $position, $salary;

}

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If a derived class has a property or method with the same name as in its parent class, the one in the derived class takes precedence.Advanced - Constructor functions are called when an object is instantiated.Advanced – Destructor functions are called when the last reference to an object is removed or the script ends.

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Advanced – Introspection allows examining an object’s characteristics (for debugging).

class_exists(classname)

get_declared_classes()

get_class_methods(classname)

get_class_vars(classname)

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Advanced – Serialization allows an object to be converted to a bytestream representation that can be stored in a file.

serialize(something)

unserialize(something)

This is commonly used with sessions to provide persistence.Now let’s look at some concrete examples.

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