Detailed introduction to PHP singleton mode, detailed introduction to PHP mode_PHP tutorial

Detailed introduction to PHP singleton mode, detailed introduction to PHP mode

The concept of singleton mode

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

Reasons and scenarios for using singleton mode

In most PHP applications, 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 large amount 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 pattern implementation

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

<&#63;php
 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();
&#63;>