Detailed introduction to PHP singleton mode_PHP tutorial

Detailed introduction to PHP singleton mode

This article mainly introduces the detailed introduction of PHP singleton mode. This article explains the concept of singleton mode, the characteristics and usage of singleton mode. The reasons and scenarios of singleton mode and PHP singleton mode code examples, friends in need can refer to it

The concept of singleton pattern

The singleton pattern refers to a design pattern in which a certain class has only one object instance in the entire application. Specifically, as a method of object creation, the singleton pattern ensures that a class has only one instance, instantiates itself and provides this instance globally to the entire system. It does not create a copy of the instance, but returns a reference to the instance stored inside the singleton class.

Characteristics of singleton pattern

The main feature of the singleton model is "three private and one public":

Requires a private static member variable that holds the only instance of the class

The constructor must be declared private to prevent external programs from newing an object and losing the meaning of the singleton

The clone function must be declared private to prevent the object from being cloned

You must provide a public static method (usually named getInstance) to access this instance, thereby returning a reference to the unique instance.

Reasons and scenarios for using singleton mode

In most applications of PHP, there will be a large number of database operations. If the singleton mode is not used, new operations will be required every time, but each new will consume a lot of system resources and memory resources, and every time you open and Closing the database is a great test and waste of the database. Therefore, the singleton pattern is often used in database operation classes.

Similarly, if a class is needed to globally control certain configuration information in the system, it can be easily implemented using the singleton mode.

PHP singleton mode implementation

The following is a framework for implementing database operation classes in PHP singleton mode

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class Db{ const DB_HOST='localhost'; const DB_NAME=''; const DB_USER=''; const DB_PWD=''; private $_db; //保存实例的私有静态变量 private static $_instance; //构造函数和克隆函数都声明为私有的 private function __construct(){ //$this->_db=mysql_connect(); } private function __clone(){ //实现 } //访问实例的公共静态方法 public static function getInstance(){ if(!(self::$_instance instanceof self)){ self::$_instance=new self(); } //或者 if(self::$_instance===null){ self::$_instance=new Db(); } return self::$_instance; } public function fetchAll(){ //实现 } public function fetchRow(){ //实现 } } //类外部获取实例的引用 $db=Db::getInstance(); ?>

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class Db{ const DB_HOST='localhost'; const DB_NAME=''; const DB_USER=''; const DB_PWD=''; private $_db; //Save the private static variables of the instance private static $_instance; //Constructor and clone functions are declared private private function __construct(){ //$this->_db=mysql_connect(); } private function __clone(){ //Implementation } //Public static methods for accessing instances public static function getInstance(){ if(!(self::$_instance instanceof self)){ self::$_instance=new self(); } //or if(self::$_instance===null){ self::$_instance=new Db(); } return self::$_instance; } public function fetchAll(){ //Implementation } public function fetchRow(){ //Implementation } } //Get the instance reference from outside the class $db=Db::getInstance(); ?>

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