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class

ÿ��Ķ��嶼�Թؼ�� class ��ͷ��һ�Ի��ţ��뷽��Ķ��塣

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һ��԰��Լ��Ϊ"��"��Լ��Ϊ"��"��

Example #1 �򵥵��ඨ��


<?php
class SimpleClass
{
    // ��������
    public $var = 'a default value';

    // ��������
    public function displayVar() {
        echo $this->var;
    }
}
?>

��һ��ඨ��ڲ��ʱ��һ��õ�α�� $this��$this ��һ��ж��ã�ͨ��Ǹ÷��Ķ��󣬵��Ǵӵڶ��̬��ʱҲ��һ��󣩡�

Example #2 $this α��ʾ��

We're assuming that error_reporting is disabled for this example; otherwise the following code would trigger deprecated and strict notices, respectively, depending on the PHP version.


<?php
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();
?>

Output of the above example in PHP 5:

$this is defined (A)
$this is not defined.
$this is defined (B)
$this is not defined.

Output of the above example in PHP 7:

$this is defined (A)
$this is not defined.
$this is not defined.
$this is not defined.

new

Ҫ��һ��ʵ��ʹ�� new �ؼ��֡��¶��ʱ�ö��Ǳ��ֵ��Ǹö��캯��ڳ��ʱ�׳��һ��쳣��Ӧ�ڱ�ʵ��֮ǰ��壨ĳЩ��

�� new ֮��ŵ��һ��ַ�� string��һ��ʵ��һ��ռ䣬��ʹ��ơ�

Example #3 ��ʵ��


<?php
$instance = new SimpleClass();

// Ҳ������������
$className = 'Foo';
$instance = new $className(); // Foo()
?>

��ඨ��ڲ�� new self �� new parent ��¶��

��һ��Ѿ��ʵ��һ��±��ʱ��±��ͬһ��ʵ��ͺ��øö��ֵһ��Ϊ�͸��ʵ��ʱһ��¡��һ��Ѵ��Ķ��һ��ʵ��

Example #4 ��ֵ


<?php

$instance = new SimpleClass();

$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);
?>

��̻��

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

PHP 5.3.0 ��·��һ��ʵ��

Example #5 ��¶��


<?php
class Test
{
    static public function getNew()
    {
        return new static;
    }
}

class Child extends Test
{}

$obj1 = new Test();
$obj2 = new $obj1;
var_dump($obj1 !== $obj2);

$obj3 = Test::getNew();
var_dump($obj3 instanceof Test);

$obj4 = Child::getNew();
var_dump($obj4 instanceof Child);
?>

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bool(true)
bool(true)
bool(true)

PHP 5.4.0 �𣬿��ͨ��һ��ʽ��´��ĳ�Ա��

Example #6 ��´��ĳ�Ա


<?php
echo (new DateTime())->format('Y');
?>

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Properties and methods

Class properties and methods live in separate "namespaces", so it is possible to have a property and a method with the same name. Referring to both a property and a method has the same notation, and whether a property will be accessed or a method will be called, solely depends on the context, i.e. whether the usage is a variable access or a function call.

Example #7 Property access vs. method call


<?php
class Foo
{
    public $bar = 'property';
    
    public function bar() {
        return 'method';
    }
}

$obj = new Foo();
echo $obj->bar, PHP_EOL, $obj->bar(), PHP_EOL;

��̻��

property
method

That means that calling an anonymous function which has been assigned to a property is not directly possible. Instead the property has to be assigned to a variable first, for instance. As of PHP 7.0.0 it is possible to call such a property directly by enclosing it in parentheses.

Example #8 Calling an anonymous function stored in a property


<?php
class Foo
{
    public $bar;
    
    public function __construct() {
        $this->bar = function() {
            return 42;
        };
    }
}

$obj = new Foo();

// as of PHP 5.3.0:
$func = $obj->bar;
echo $func(), PHP_EOL;

// alternatively, as of PHP 7.0.0:
echo ($obj->bar)(), PHP_EOL;

��̻��

extends

һ�� extends �ؼ��ּ̳��һ��ķ��ԡ�PHP��֧�ֶ��ؼ̳У�һ��ֻ�ܼ̳�һ��ࡣ

��̳еķ��Կ��ͨ��ͬ��ǡ��ඨ�巽��ʱʹ�� final��÷��ɱ��ǡ��ͨ�� parent:: ��ʱ��ǵķ��ԡ�

��Ƿ��ʱ��뱣��һ�·�� PHP �� E_STRICT ��Ĵ��Ϣ��캯��⣬��캯��ڱ��ʱʹ�ò�ͬ�Ĳ��

Example #9 �򵥵��̳�


<?php
class ExtendClass extends SimpleClass
{
    // Redefine the parent method
    function displayVar()
    {
        echo "Extending class\n";
        parent::displayVar();
    }
}

$extended = new ExtendClass();
$extended->displayVar();
?>

��̻��

Extending class
a default value

::class

�� PHP 5.5 �𣬹ؼ�� class Ҳ��Ľ��ʹ�� ClassName::class ��Ի�ȡһ��ַ�� ClassName ��ȫ�޶��ơ��ʹ�� ռ� ��á�

Example #10 ��Ľ��


<?php
namespace NS {
    class ClassName {
    }
    
    echo ClassName::class;
}
?>

��̻��

NS\ClassName

Note:
The class name resolution using ::class is a compile time transformation. That means at the time the class name string is created no autoloading has happened yet. As a consequence, class names are expanded even if the class does not exist. No error is issued in that case.

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class

new

Properties and methods

extends

::class

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