设计模式单例示例【PHP】

<?php
class Car {
    private static $instance;
    private function __clone(){}
    private function __construct() {}
    public static function getInstance()
    {
        if ( self::$instance instanceof self ) {
            return self::$instance;
        } else {
            return self::$instance = new self();
        }
    }
    public function getColor()
    {
        return 'red';
    }
}
$car = Car::getInstance();
echo $car->getColor();