PHP设计模式之：单例模式

<?php
class Danli {

//保存类实例的静态成员变量
private static $_instance;

//private标记的构造方法
private function __construct(){
echo 'This is a Constructed method;';
}

//创建__clone方法防止对象被复制克隆
public function __clone(){
trigger_error('Clone is not allow!',E_USER_ERROR);
}

//单例方法,用于访问实例的公共的静态方法
public static function getInstance(){
if(!(self::$_instance instanceof self)){
self::$_instance = new self;
}
return self::$_instance;
}

public function test(){
echo '调用方法成功';
}

}

//用new实例化private标记构造函数的类会报错
//$danli = new Danli();

//正确方法,用双冒号::操作符访问静态方法获取实例
$danli = Danli::getInstance();
$danli->test();

//复制(克隆)对象将导致一个E_USER_ERROR
//$danli_clone = clone $danli;