PHP: Object-Oriented Prorgamming

Overview

Object-oriented programming (OOP) is a method of programming that involves the following:

• Programs are organized around "objects" and data, not just the process. Objects represent real-world things. Objects have "attributes" and "behaviors".
• A "class" is a definition of objects of the same kind. It is a blueprint, template, or prototype that defines and describes the static attributes and behaviors common to all objects of the same kind.
  • person class: attributes (name, height, weight, gender, age); behaviors (speak, walk, sleep). In other words, attributes are the "data", behavior is "functions".
  • Many languages use the terms properties" to describe "attributes" and "methods" to describe "behaviors".
  • Classes describe things in "abstract" terms. Class is just the description, not the actual person or persons name.
  • Inheritance − When a class is defined by inheriting existing function of a parent class then it is called inheritance. Here child class will inherit all or few member functions and variables of a parent class.
  • Parent class − A class that is inherited from by another class. Also known as base class or super class.
  • Child Class − A class that inherits from another class. Also known as subclass or derived class.
• An "instance" is a realization of a particular item of a class. An instance is an instantiation of a class. All the instances of a class have similar properties, as described in the class definition.
  • For example, you can define a class called "Employee" and create three instances of the class "Employee" for "Mark Smith" and "Mary Jones".
  • The term "object" usually refers to instance. An object, or multiple objectis, are created from a class.
• Relationships can be created between objects, e.g. one object can inherit characteristics from another object.
• Encapsuation - classes are self-contained units that reprepsent both the data and the code that works on that data: the properties and methods (bundling data and methods).
• Benefits:
  1. Modularity
  2. Information-hiding
  3. Code re-use ("Don't Repeat Yourself" - DRY)
  4. Pluggability and debugging ease
  5. Easy to maintain code.

	<?php
	  class Car 
	  {
		  // Member variables
		  var $price;
		  
		  // Member functions 
		  function setModel($par){
			 $this->model = $par;
		  }
		  
		  function getModel(){
			 echo "<p>Model: " . $this->model . "</p>";
		  }

		  function setPrice($par){
			 $this->price = $par;
		  }
		  
		  function getPrice(){
			 echo "<p>Price: $" . $this->price . ".</p>";
		  }	  
	  }
	  
	  // Create objects
	  $grandcher2018 = new Car;

	  // Call member functions
	  $grandcher2018->setModel( "Jeep Grand Cherokee" );
	  $grandcher2018->setPrice( 30695 );
	  
	  $grandcher2018->getModel();
	  $grandcher2018->getPrice();

	?>