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。
<?php
class Fruit {
const CONST_VALUE = 'Fruit Color';
}
$classname = 'Fruit';
echo $classname::CONST_VALUE; // As of PHP 5.3.0
echo Fruit::CONST_VALUE;
?>
<?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：
Fruit Color Red
<?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：
Fruit::showColor() Apple::showColor()
<?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：
Banana is yellow
<?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：
show color
