Introduction to ObjectOriented Programming with PHP 5

1
Chapter 4

• Introduction to Object-Oriented Programming with
  PHP 5

2
Why Create Objects?

• Helps manage complexity within projects.
• Increases code reusability thereby reducing
  maintenance cost.

3
Classes and Objects

• Object can be almost any item or concept such as
  a desk or a customer
• Conceptual objects also exist but usually only in
  software
• Text input area or a file.
• Classes represents a set of objects that might
  vary from individual to individual but have a
  certain amount of attributes and operations in
  common
• Cars and bikes.

4
Attributes and Operations

• OO software is designed and built as a set of
  self-contained objects with both attributes and
  operations
• Attributes are also called member variables or
  properties.
• Operations are also called methods.

5
Encapsulation

• Also known as data hiding.
• Data within the object is available only via the
  objects operations (the interface of the object.
• Encapsulation give the programmer a way to ensure
  that function calls to their object wont
  accidentially change the variable settings of the
  class.

6
Structure of a Class

• class classname
• // member variables
• var attribute1
• var attribute2
• //operations
• function operation1()
• function operation2(param1, param2)

7
UnitCounter Example

• lt?php
• class UnitCounter
• // member variables
• var units 0
• var weightPerUnit 1.0
• // operations
• // Add n to the total number of units,
  default1
• function add(n 1)
• this-gtunits this-gtunits n
• function totalWeight()
• return this-gtunits this-gtweightPerUnit
• ?gt

8
Constructors

• A constructor is a special type of operation.
• A constructor is automatically called when an
  object is created.
• Its function is usually to perform useful
  initialization tasks such as setting attributes
  to sensible starting values or defining ranges
  for attributes.
• Although they are called automatically, you can
  call them using the __contruct(param). This is
  new in PHP5. PHP4 used the convention of the
  constructor having the same name as the object.

9
Instantiating a Class

• After you have created a class, you will want to
  use it. This is called instantiation or creating
  an instance of the class.
• Try it with the following code example

10
Instantiating a Class, Example

• lt?php
• class classname
• function __construct(param)
• echo 'Constructor called with parameter ' .
  param . 'ltbr /gt'
• a new classname(First)
• b new classname(Second)
• c new classname()
• ?gt