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                ## 單例模式 #### 特點: 三私一公:私有的靜態變量(存放實例),私有的構造方法(防止創建實例),私有的克隆方法(防止克隆對象),公有的靜態方法(對外界提供實例) 應用場景: 程序應用中,涉及到數據庫操作時,如果每次操作的時候連接數據庫,會帶來大量的資源消耗。可以通過單例模式,創建唯一的數據庫連接對象。 ``` <?php class Singleton { private static $_instance; private function __construct(){} private function __clone(){} public static function getInstance() { if(self::$_instance instanceof Singleton){//instanceof 判斷一個實例是否是某個類的對象 self::$_instance = new Singleton(); } return self::$_instance; } } ```
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