為啥這樣寫(xiě)
?private?static?$_object?=?null;
????public?static?function?getInstance()?{
????????//empty?檢查變量是否為空
????????if?(empty(self::$_object))?{
????????????self::$_object?=?new?Car22();?//內(nèi)部方法可以調(diào)用私有方法，因此這里可以創(chuàng)建對(duì)象
????????}
????????return?self::$_object;
????}
}私有方法給賦值不為空 ，那下面打印?$_object?的值不出來(lái)?
