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Object-Oriented Programming with PHP
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Extending your class


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Object-Oriented Programming with PHP

with Jon Peck

Video: Extending your class

In this chapter, I'm going to introduce class hierarchies. First, I'm going to demonstrate how classes can relate to one another. Then I'll show how to create blueprints for classes and methods. We'll make unified interfaces with polymorphic behaviors. I'll demonstrate how to override methods, properties, and even constants. We'll copy and compare objects, then finally explore ways that objects can be manipulated indirectly. Before we go any further, I'd like to teach you a neat way of dealing with large numbers of class files gracefully.
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  1. 4m 10s
    1. Welcome
      39s
    2. Exercise files
      2m 16s
    3. What you should know
      1m 15s
  2. 7m 47s
    1. What is an object?
      2m 6s
    2. What is a class?
      2m 7s
    3. Why should you use object-oriented programming?
      2m 14s
    4. The history of object-oriented PHP
      1m 20s
  3. 16m 40s
    1. Defining a class
      2m 58s
    2. Defining class properties
      3m 26s
    3. Creating a method and exploring object context with $this
      2m 50s
    4. Instantiating an object and accessing its contents
      3m 19s
    5. Specifying the visibility scope
      4m 7s
  4. 15m 51s
    1. What is a magic method, and do I need one?
      2m 23s
    2. Overloading property access
      6m 37s
    3. Customizing object construction
      4m 34s
    4. Standardizing object rendering as a string
      2m 17s
  5. 20m 54s
    1. Using the static keyword
      3m 36s
    2. Leveraging scope resolution operators
      1m 10s
    3. Setting constant values
      2m 47s
    4. Implementing static methods
      5m 43s
    5. Creating a database class
      7m 38s
  6. 26m 19s
    1. Extending your class
      6m 8s
    2. Abstracting classes
      5m 57s
    3. Sharing interfaces using polymorphism
      4m 39s
    4. Overriding methods, properties, and constants
      3m 25s
    5. Cloning and comparing objects
      2m 51s
    6. Referencing objects
      3m 19s
  7. 14m 52s
    1. Leveraging standard class objects
      2m 42s
    2. Retrieving objects from the database
      5m 41s
    3. Error handling with exceptions
      2m 6s
    4. Customizing PHP exceptions
      4m 23s
  8. 8m 2s
    1. Identifying the singleton pattern
      1m 42s
    2. Using the factory method pattern
      1m 51s
    3. Implementing a strategy pattern
      4m 29s
  9. 2m 57s
    1. Looking forward to namespaces
      47s
    2. Next steps
      1m 6s
    3. Goodbye
      1m 4s

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Object-Oriented Programming with PHP
1h 57m Intermediate Sep 26, 2012 Updated Apr 10, 2013

Viewers: in countries Watching now:

Whether you're enhancing or optimizing existing code or just starting from scratch, there's never a better time to start integrating object-oriented design techniques. This course shows how to integrate the principles of object-oriented programming into the build of a PHP-driven web page or application. After an overview of what objects and classes are and why they should be used, author Jon Peck dives into creating and instantiating objects, then defining the class relationships and interactions that will form the basis of your coding arsenal. The course also shows how to leverage PHP objects and implement design patterns, and looks at steps you can take to continue adding to your programming tool belt.

Topics include:
  • Historical overview of object-oriented PHP
  • Defining classes
  • Creating a method/object context with $this
  • Accessing classes without instantiation
  • Creating a database class
  • Extending and abstracting classes
  • Cloning and comparing objects
  • Error handling with exceptions
  • Implementing design patterns, such as the factory and strategy patterns
Subjects:
Developer Programming Languages
Software:
PHP
Author:
Jon Peck

Extending your class

In this chapter, I'm going to introduce class hierarchies. First, I'm going to demonstrate how classes can relate to one another. Then I'll show how to create blueprints for classes and methods. We'll make unified interfaces with polymorphic behaviors. I'll demonstrate how to override methods, properties, and even constants. We'll copy and compare objects, then finally explore ways that objects can be manipulated indirectly. Before we go any further, I'd like to teach you a neat way of dealing with large numbers of class files gracefully.

Currently in the demo file, we're explicitly requiring both the address and the database class. However, as we add more classes with one file per class, things are going to get a bit messy with more requires. Good thing there is another option. As of PHP 5, a new solution was added, known as Autoloading classes. If you define an autoload function, it will automatically be called whenever you try to access a class that hasn't been defined yet, kind of like a failsafe before PHP gives up, and has a fatal error.

I am going to replace the two require statements at the top of the demo with an autoload function definition. function __autoload, which takes one argument. $class_name. include anything that starts with 'class.' and then the class_name.inc. Define autoloader with one parameter string $class_name. Save the file.

Now that we future-proofed the application, let's discuss inheritance. Inheritance is a core object-oriented principle, where relationship between classes can be established. Think of it as a parent and child relationship, where the parent is a class, and a child is a subclass of the parent. The child inherits all of the parent's behaviors and properties, making it an inclusive superset of both the child and the parent. There are a number of characteristics of inheritance that are useful. Both the parent and the child share common functionality, without having to copy and paste code.

The child can have new functionality that the parent does not. Therefore, the child extends the parent, which is also the key word used. The only way that a child can extend a parent is if the parent has been declared. Classes can extend only one class's methods and properties at a time. You can't specify multiple classes to extend. You can, on the other hand, extend a class that extends another class. You just can't extend two classes simultaneously. This is a lot to think about, so let's see it in action.

In the previous chapter, we added a property to the address class to track what type of an address an object was: a residence, business, or park. I want to avoid code duplication, but still be able to add address type specific behavior. Therefore, I'll make address a parent class, and make child classes for the three address types. We'll implement unique behaviors in the next segment. I'm going to switch back to the IDE. In the previous chapter, you added a property to the Address class to track what type of an address an object was: a residence, business or park.

For this exercise, I'm going to assign a different behavior to each address type. You'll implement that behavior in the next video, but to do so, you'll need a place to put it. Start the class definition with the name of the class, followed by the keyword extends, then the name of the class you are extending. PHP label conventions apply to the name of the class, but best practice is to start with the name of the class you are extending. Create a new file in your Exercise folder called class.AddressResidence.inc.

Start the class definition with the name of the class, followed by the keyword extends, then the name of the class you're extending. PHP label conventions apply to the name of the class, but the best practice is to start with the name of the class you're extending. class AddressResidence extends Address. Add quick documentation, and save. That's all that needs to be added for now as different behavior will be defined later.

Next, create a new file for the business address called class.AddressBusiness. The contents will be virtually identical. Save, then create the final file for a park address. class.AddressPark.inc.

And then, class.AddressPark extends Address. Save, and return to the demo file. Following the autoloader, change the title to AddressResidence. Address is new AddressResidence. And, re-factor the remaining code. Add debugging to display the contents of the address_residence variable. echo

 var_export{$address_ residence, TRUE} close pre, close tt.
						
					

Save, then switch to your browser. When you refresh the page, you will see that the class is now address_residence, and that all the functionality that you previously defined in the Address class still works, and is still accessed in the same manner. Also note that the second address, which is just class address, functions as it was before, even as a parent. In the next video, I'll demonstrate how to prevent the use of the parent address, and how to add custom behaviors to the child classes.

Find answers to the most frequently asked questions about Object-Oriented Programming with PHP.


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Q: I'm not seeing warnings or errors in my environment like the video; why not?
A: Your PHP configuration is probably configured not to show them to you. This is often true on commercial web hosts and is often the default. Fortunately, there are multiple ways of resolving this.

The easiest way would be to explicitly enable error reporting at the top of the PHP script you wish to debug.

error_reporting(E_ALL | E_STRICT);
ini_set('display_errors', 1);

Alternatively, if you have access to your php.ini file and you want to always have error reporting on, change error_reporting = to a development friendly value of

error_reporting = E_ALL | E_STRICT

then change display_errors = to

display_errors = On

Finally, if access to the php.ini file is not available, you can add the following directives to your .htaccess or VirtualHost configuration for Apache:

php_value error_reporting 32767
php_value display_errors 1

If you would like a development optimized development environment like the one utilized in this course, see Up and Running with Linux for PHP Developers, here in the lynda.com online training library.

Q: This course was updated on 4/10/2013. What changed?

A: The author rerecorded some of the tutorials to add more background information and better graphics.

 

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