PHP. Руководство по PHP. 2005

The BasicsПред.Глава 19. Классы и объекты (PHP 5)След.

The Basics

class

Every class definition begins with the keyword class, followed by a class name, which can be any name that isn't a reserved word in PHP. Followed by a pair of curly braces, of which contains the definition of the classes members and methods. A pseudo-variable, $this is available when a method is called from within an object context. $this is a reference to the calling object (usually the object to which the method belongs, but can be another object, if the method is called statically from the context of a secondary object). This is illustrated in the following example:


<?
class A
{
function foo()
{
if (isset($this)){
echo '$this is defined (';
echo get_class($this);
echo ")\n";
}else{
echo "\$this is not defined.\n";
}}
}
class B
{
function bar()
{
A::foo();
}}
$a = new A();
$a->foo();
A::foo();
$b = new B();
$b->bar();
B::bar();

?>

Результат выполнения данного примера:

$this is defined (a)
$this is not defined.
$this is defined (b)
$this is not defined.

Пример 19-1. Simple Class definition


<?
class SimpleClass
{
//member declaration
public $var = 'a default value';
//method declaration
public function displayVar(){
echo $this->var;
}}

?>

new

To create an instance of an object, a new object must be created and assigned to a variable. An object will always be assigned when creating a new object unless the object has a constructor defined that throws an exception on error.

Пример 19-2. Creating an instance


<?
$instance = new SimpleClass()

?>

When assigning an already created instance of an object to a new variable, the new variable will access the same instance as the object that was assigned. This behaviour is the same when passing instances to a function. A new instance of an already created object can be made by cloning it.

Пример 19-3. Object Assignment


<?
$assigned = $instance;
$reference =& $instance;
$instance->var = '$assigned will have this value';
$instance = null; //$instance and $reference become null
var_dump($instance);
var_dump($reference);
var_dump($assigned);

?>

Результат выполнения данного примера:

NULL
NULL
object(SimpleClass)#1 (1){ ["var"]=> string(30) "$assigned will have this value"
}

extends

A class can inherit methods and members of another class by using the extends keyword in the declaration. It is not possible to extend multiple classes, a class can only inherit one base class.

The inherited methods and members can be overridden, unless the parent class has defined a method as final, by redeclaring them within the same name defined in the parent class. It is possible to access the overrided method or members by referencing them with parent::

Пример 19-4. Simple Class Inherintance


<?
class ExtendClass extends SimpleClass
{
//Redefine the parent method
function displayVar()
{
echo "Extending class\n";
parent::displayVar();
}}
$extended = new ExtendClass();
$extended->displayVar();

?>

Результат выполнения данного примера:

Extending class

a default value

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Классы и объекты (PHP 5)

Уровень выше

Autoloading Objects

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