双冒号操作符即作用域限定操作符Scope Resolution Operator可以访问静态、const和类中重写的属性与方法。
在类定义外使用的话,使用类名调用。在PHP 5.3.0,可以使用变量代替类名。
Program List:用变量在类定义外部访问
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<?php class Fruit {
const CONST_VALUE = 'Fruit Color' ;
} $classname = 'Fruit' ;
echo $classname ::CONST_VALUE; // As of PHP 5.3.0
echo Fruit::CONST_VALUE;
?> |
Program List:在类定义外部使用::
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<?php class Fruit {
const CONST_VALUE = 'Fruit Color' ;
} class Apple extends Fruit
{ public static $color = 'Red' ;
public static function doubleColon() {
echo parent::CONST_VALUE . "\n" ;
echo self:: $color . "\n" ;
}
} Apple::doubleColon(); ?> |
程序运行结果:
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Fruit Color Red |
Program List:调用parent方法
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<?php class Fruit
{ protected function showColor() {
echo "Fruit::showColor()\n" ;
}
} class Apple extends Fruit
{ // Override parent's definition
public function showColor()
{
// But still call the parent function
parent::showColor();
echo "Apple::showColor()\n" ;
}
} $apple = new Apple();
$apple ->showColor();
?> |
程序运行结果:
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Fruit::showColor() Apple::showColor() |
Program List:使用作用域限定符
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<?php class Apple
{
public function showColor()
{
return $this ->color;
}
}
class Banana
{
public $color ;
public function __construct()
{
$this ->color = "Banana is yellow" ;
}
public function GetColor()
{
return Apple::showColor();
}
}
$banana = new Banana;
echo $banana ->GetColor();
?> |
程序运行结果:
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Banana is yellow |
Program List:调用基类的方法
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<?php class Fruit
{ static function color()
{
return "color" ;
}
static function showColor()
{
echo "show " . self::color();
}
} class Apple extends Fruit
{ static function color()
{
return "red" ;
}
} Apple::showColor(); // output is "show color"! ?> |
程序运行结果:
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show color |