Tag Archives: Education

Some Notes on the Object-oriented Model of PHP

PHP 5 introduces interfaces and abstract classes. To become a little clearer, let us see their definitions.

Interfaces

Object interfaces allow you to create code which specifies which methods a class must implement, without having to define how these methods are handled.
Interfaces are defined using the interface keyword, in the same way as a standard class, but without any of the methods having their contents defined.
All methods declared in an interface must be public, this is the nature of an interface.

To implement an interface, the implements operator is used. All methods in the interface must be implemented within a class; failure to do so will result in a fatal error. Classes may implement more than one interface if desired by separating each interface with a comma.

Abstract Classes

PHP 5 introduces abstract classes and methods. Classes defined as abstract may not be instantiated, and any class that contains at least one abstract method must also be abstract. Methods defined as abstract simply declare the method’s signature – they cannot define the implementation.

When inheriting from an abstract class, all methods marked abstract in the parent’s class declaration must be defined by the child; additionally, these methods must be defined with the same (or a less restricted) visibility. For example, if the abstract method is defined as protected, the function implementation must be defined as either protected or public, but not private. Furthermore the signatures of the methods must match, i.e. the type hints and the number of required arguments must be the same. This also applies to constructors as of PHP 5.4. Before 5.4 constructor signatures could differ.

Some Cases

Now let’s do a quick experiment. According to the definition of interfaces we can define an interface and than an abstract class can implement this interface.
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Object Oriented JavaScript: Inheritance

Objects and JavaScript

JavaScript, being a functional language, differs from most of the procedural/object oriented languages we know. The object oriented approach in JavaScript is rather strange. However there is much power in making objects! The syntax is really odd and there are several approaches.

Literal Notation

As many of you may know the most used notation is the JSON (JavaScript Object Notation).

{ 'key1' : 'val1'
, 'key2' : 'val2'
, 'key3' : 'val3'
}

Of course this is the very basic example. You can use as value any JavaScript object – another similar object or a function.

{ 'key1' : 'val1'
, 'key2' : { 'inner_key1' : 'inner_val1' }
, 'key3' : function() {
			return 10 + 5;
		 }
}

The two examples above are showing an anonymous object in JavaScript, but you can assign this code to some variable.

var myObject = 
	{ 'key1' : 'val1'
	, 'key2' : 'val2'
	, 'key3' : 'val3'
	}

or

var myObject =
	{ 'key1' : 'val1'
	, 'key2' : { 'inner_key1' : 'inner_val1' }
	, 'key3' : function() {
				return 10 + 5;
			 }
	}

and then you can call the properties of these objects with the ‘.’ operator:

myObject.key1;
myObject.key2.inner_key1;
myObject.key3();

So far so good – this is the literal object notation in JavaScript. However there is another “objects” in JavaScript.
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Models in Zend Framework – Initialize All Methods with init()

In the Zend Framework’s documentation there are lots of examples how you can initialize all the actions in a given controller – by simply adding the init() public method in the controller’s code:

<?php
 
class IndexController extends Zend_Controller_Action
{
	public function init()
	{
		echo 'foo';	
	}	
 
	public function indexAction()
	{
		// first the 'foo' string will be printed
		echo 'bar';	
	}
}

But did you know that you can do the same thing with any model in ZF? However you can setup a cache for every method or something else, but definitely it will execute for every method:

<?php
 
class MyModel
{
	public function init()
	{
		// prepare the cache setup
	}	
 
	public function readAll()
	{
		// the cache is already setup
		$sql = '...';
		// ...
	}
}

Of course that means that directly calling the readAll() function the init() method is called also – automatically.

Conclusion

There are good and bad parts about this. You’ll have this code executed for every method and if you have twenty of them and the init() method is practically used for only a couple of the member functions – than this will be useless.