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 |
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class Fruit { |
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const CONST_VALUE = 'Fruit Color'; |
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} |
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$classname = 'Fruit'; |
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echo $classname::CONST_VALUE; // As of PHP 5.3.0 |
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echo Fruit::CONST_VALUE; |
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?> |
Program List：在类定义外部使用::
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<?php |
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class Fruit { |
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const CONST_VALUE = 'Fruit Color'; |
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} |
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class Apple extends Fruit |
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{ |
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public static $color = 'Red'; |
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public static function doubleColon() { |
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echo parent::CONST_VALUE . "\n"; |
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echo self::$color . "\n"; |
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} |
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} |
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Apple::doubleColon(); |
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?> |
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 |
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class Fruit |
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{ |
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protected function showColor() { |
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echo "Fruit::showColor()\n"; |
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} |
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} |
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class Apple extends Fruit |
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{ |
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// Override parent's definition |
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public function showColor() |
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{ |
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// But still call the parent function |
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parent::showColor(); |
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echo "Apple::showColor()\n"; |
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} |
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} |
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$apple = new Apple(); |
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$apple->showColor(); |
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?> |
程序运行结果：
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Fruit::showColor() |
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Apple::showColor() |
Program List：使用作用域限定符
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<?php |
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class Apple |
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{ |
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public function showColor() |
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{ |
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return $this->color; |
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} |
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} |
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class Banana |
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{ |
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public $color; |
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public function __construct() |
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{ |
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$this->color = "Banana is yellow"; |
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} |
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public function GetColor() |
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{ |
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return Apple::showColor(); |
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} |
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} |
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$banana = new Banana; |
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echo $banana->GetColor(); |
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?> |
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 |
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class Fruit |
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{ |
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static function color() |
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{ |
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return "color"; |
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} |
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static function showColor() |
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{ |
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echo "show " . self::color(); |
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} |
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} |
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class Apple extends Fruit |
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{ |
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static function color() |
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{ |
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return "red"; |
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} |
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} |
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Apple::showColor(); |
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// output is "show color"! |
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?> |
程序运行结果：
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show color |
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