Singleton(单例模式):单例模式是最常见的模式之一，在Web应用的开发中，常常用于允许在运行时为某个特定的类创建仅有一个可访问的实例。
<?php/** * Singleton class[单例模式] * @author ITYangs<ityangs@163.com> */final class Mysql{ ???/** ????* ????* @var self[该属性用来保存实例] ????*/ ???private static $instance; ???/** ????* ????* @var mixed ????*/ ???public $mix; ???/** ????* Return self instance[创建一个用来实例化对象的方法] ????* ????* @return self ????*/ ???public static function getInstance() ???{ ???????if (! (self::$instance instanceof self)) { ???????????self::$instance = new self(); ???????} ???????return self::$instance; ???} ???/** ????* 构造函数为private,防止创建对象 ????*/ ???private function __construct() ???{} ???/** ????* 防止对象被复制 ????*/ ???private function __clone() ???{ ???????trigger_error(‘Clone is not allowed !‘); ???}}// @test$firstMysql = Mysql::getInstance();$secondMysql = Mysql::getInstance();$firstMysql->mix = ‘ityangs_one‘;$secondMysql->mix = ‘ityangs_two‘;print_r($firstMysql->mix);// 输出： ityangs_twoprint_r($secondMysql->mix);// 输出： ityangs_two在很多情况下，需要为系统中的多个类创建单例的构造方式，这样，可以建立一个通用的抽象父工厂方法：
<?php/** * Singleton class[单例模式:多个类创建单例的构造方式] * @author ITYangs<ityangs@163.com> */abstract class FactoryAbstract { ???protected static $instances = array(); ???public static function getInstance() { ???????$className = self::getClassName(); ???????if (!(self::$instances[$className] instanceof $className)) { ???????????self::$instances[$className] = new $className(); ???????} ???????return self::$instances[$className]; ???} ???public static function removeInstance() { ???????$className = self::getClassName(); ???????if (array_key_exists($className, self::$instances)) { ???????????unset(self::$instances[$className]); ???????} ???} ???final protected static function getClassName() { ???????return get_called_class(); ???} ???protected function __construct() { } ???final protected function __clone() { }}abstract class Factory extends FactoryAbstract { ???final public static function getInstance() { ???????return parent::getInstance(); ???} ???final public static function removeInstance() { ???????parent::removeInstance(); ???}}// @testclass FirstProduct extends Factory { ???public $a = [];}class SecondProduct extends FirstProduct {}FirstProduct::getInstance()->a[] = 1;SecondProduct::getInstance()->a[] = 2;FirstProduct::getInstance()->a[] = 11;SecondProduct::getInstance()->a[] = 22;print_r(FirstProduct::getInstance()->a);// Array ( [0] => 1 [1] => 11 )print_r(SecondProduct::getInstance()->a);// Array ( [0] => 2 [1] => 22 )PHP设计模式 - 单例模式
原文地址：https://www.cnblogs.com/taozi32/p/9226441.html