In this final installment of the series I'm going to show you how to develop an expandable PHP mechanism for validating different types of incoming data. This will demonstrate how this important pillar of object-oriented programming can be used with a plethora of applications.

They show how to create a simple DataValidator class to act as a base to build from. On top of this, they create classes to validate if the value is:

• empty
• an integer
• if it's numeric
• if it's in a certain range
• if it's alphanumeric
• if it's alphabetic
• or if it's a valid email address

In short, Polymorphism is a feature exposed by certain objects that belong to the same family, which eventually can behave differently, even when they're using identical methods. Or more clearly, an object can be considered polymorphic when it's capable of performing different actions by utilizing the same method.

This time they focus on web page development that uses this object-oriented practice. The create a WebPageElement that you can ID and class attributes on and use it to create HTML widgets and extend them to create Div and Link element.

I'll be explaining how to implement Polymorphism to achieve a high level of abstraction when accessing different database systems. Subsequent articles will cover the use of polymorphic objects to build dynamic web documents and validate user-supplied input.

They start out with a bad example of a database link in a PHP script, a database handler that, based on what type of database you tell it you're using, handles the requests appropriately. This is good, but poor design - their alternative is using objects (created from classes of one type for each kind of database). These are pulled together in a factory class and the correct one is built - out into a generic database object that's smart enough to know what it's supposed to do.

Last week, we continued our discussion of the object-oriented features of PHP 5 by taking a first look at design patterns. This week, we will continue looking at design patterns, and examine polymorphism. This article, the third of four parts, is excerpted from chapter two of the book Advanced PHP Programming, written by George Schlossnagle.

They cover some of the more handy features OOP in PHP5, including interfaces, type hinting, the factory pattern and the singleton pattern.

In "Part 1: Definition" we took a look at defining objects and classes in PHP. In "Part 2: Relationships" we looked at linking our objects and classes together. In part 3 I'm going to add to those relationships by looking at visibility, polymorphism and the scope resolution operator.

He starts off with a look at access modifiers (private, public, protected) on both attributes and methods. Next is a look at polymorphism with an example of using a getHTML function in both a base formElement class and the child class of textarea. He then talks about the scope resolution operator (::) and its use in parent/child relationships and in PHP5's scope.

If you are working with classes in PHP, you will sooner or later encounter inheritance, polymorphism, and serialization. The ability to use these three will help speed up your code writing. This article covers how to use them, and more.

First off, they look at inheritance and working with child classes before moving on to polymorphism (similar functionality, different objects), calling functions statically, and serializing objects to make passing them around much easier.

This article explains what polymorphism is and how it applies to object oriented design in particular. It also explains the pros and cons of polymorphism when working with certain versions of PHP.

They start with a definition on the topic that doesn't seem to help much: "The occurrence of different forms, stages, or types in individual organisms or in organisms of the same species, independent of sexual variations." They do, however, follow that with what it means to programming: "...an interface or base class without regard to an object's concrete class." They also include a simple example (no code, that's later).

With that concept in place, they move to the next step - working with the example to create code that can be used as a reference point. They talk about using a switch to make the script respond differently to different inputs and the lack of "late binding" support in PHP5.]]> Tue, 07 Mar 2006 07:19:08 -0600