PHP作用域限定符双冒号::的用法

    
<?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();
?>

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();
?>

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();
?>

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"!
?>

show color