class test{
    static private $_instance;

    public static function getInstance()
    {
        if(empty(self::$_instance))
        {
            self::$_instance =new test();
        }

        return self::$_instance;
    }
    public function my()
    {
        echo ‘mymy‘;
    }
}
//$obj1,$obj2,$obj3相等
$obj1=test::getInstance();
$obj2=test::getInstance();
$obj3=test::getInstance();

//输出mymy
echo $obj3->my();