设计模式初探之单例模式

<?php
/**
 * @note 懒汉式单例模式
 */
class Singleton{
    //类实例
    public static $instance;
    public $a;

    public static function getInstance()
    {
        if(!(self::$instance instanceof self)){
            self::$instance = new self();
        }
        return self::$instance;
    }
    /**
     * @note 私有化克隆方法防止克隆
     */
    private function __clone()
    {

    }

}

$first = Singleton::getInstance();
//$first = new Singleton();
$second = Singleton::getInstance();
//$second = new Singleton();

//$first->a = '222222222222222';
//$second->a = 111111111111111;

echo '<pre>';
var_dump($first);
var_dump($second);