Memo pattern is a behavioral pattern that captures the internal state of an object and saves this state outside the object without destroying encapsulation. This allows you to later restore the object's state to its previously saved state.
Main role
Memento role: Stores the internal state of the originator object, and the originator decides which internal states of the originator are stored in the memento as needed. A memento can protect its contents from being read by any object other than the originator object.
Originator role: Create a memo object containing the current internal state, and use the memo object to store its internal state.
Caretaker role: Responsible for saving the memo object and not checking the contents of the memo object.
Applicable Property
Must save the (partial) state of an object at a certain moment so that it can be restored to its previous state when needed later.
If an interface is used to allow other objects to directly obtain these states, it will expose the implementation details of the object and destroy the encapsulation of the object.
Class diagram
Instances
<?php class Originator { // 发起人(Originator)角色 private $_state; public function __construct() { $this->_state = ''; } public function createMemento() { // 创建备忘录 return new Memento($this->_state); } public function restoreMemento(Memento $memento) { // 将发起人恢复到备忘录对象记录的状态上 $this->_state = $memento->getState(); } public function setState($state) { $this->_state = $state; } public function getState() { return $this->_state; } public function showState() {} } class Memento { // 备忘录(Memento)角色 private $_state; public function __construct($state) { $this->setState($state); } public function getState() { return $this->_state; } public function setState($state) { $this->_state = $state;} } class Caretaker { // 负责人(Caretaker)角色 private $_memento; public function getMemento() { return $this->_memento; } public function setMemento(Memento $memento) { $this->_memento = $memento; } } // client /* 创建目标对象 */ $org = new Originator(); $org->setState('open'); $org->showState(); /* 创建备忘 */ $memento = $org->createMemento(); /* 通过Caretaker保存此备忘 */ $caretaker = new Caretaker(); $caretaker->setMemento($memento); /* 改变目标对象的状态 */ $org->setState('close'); $org->showState(); /* 还原操作 */ $org->restoreMemento($caretaker->getMemento()); $org->showState(); ?>
Advantages and disadvantages
Advantages
Sometimes some internal information of the initiator object must be saved outside the initiator object, but it must be read by the initiator object itself.
Simplified the Originator class. The Originator no longer needs to manage and save versions of its internal states. Clients can manage the versions of these states they need by themselves
When the status of the Originator role changes, it is possible that the status is invalid. At this time, you can use the temporarily stored memo to restore the status.
Disadvantages
If the status of the initiator role needs to be completely stored in the memo object, the memo object will be very expensive in terms of resource consumption.
When the person in charge stores a memo, the person in charge may not know how much storage space this status will occupy, and thus cannot remind the user whether an operation will be expensive.
When the status of the initiator role changes, the status may be invalid.

php把负数转为正整数的方法:1、使用abs()函数将负数转为正数,使用intval()函数对正数取整,转为正整数,语法“intval(abs($number))”;2、利用“~”位运算符将负数取反加一,语法“~$number + 1”。

实现方法:1、使用“sleep(延迟秒数)”语句,可延迟执行函数若干秒;2、使用“time_nanosleep(延迟秒数,延迟纳秒数)”语句,可延迟执行函数若干秒和纳秒;3、使用“time_sleep_until(time()+7)”语句。

php除以100保留两位小数的方法:1、利用“/”运算符进行除法运算,语法“数值 / 100”;2、使用“number_format(除法结果, 2)”或“sprintf("%.2f",除法结果)”语句进行四舍五入的处理值,并保留两位小数。

判断方法:1、使用“strtotime("年-月-日")”语句将给定的年月日转换为时间戳格式;2、用“date("z",时间戳)+1”语句计算指定时间戳是一年的第几天。date()返回的天数是从0开始计算的,因此真实天数需要在此基础上加1。

方法:1、用“str_replace(" ","其他字符",$str)”语句,可将nbsp符替换为其他字符;2、用“preg_replace("/(\s|\ \;||\xc2\xa0)/","其他字符",$str)”语句。

php判断有没有小数点的方法:1、使用“strpos(数字字符串,'.')”语法,如果返回小数点在字符串中第一次出现的位置,则有小数点;2、使用“strrpos(数字字符串,'.')”语句,如果返回小数点在字符串中最后一次出现的位置,则有。

php字符串有下标。在PHP中,下标不仅可以应用于数组和对象,还可应用于字符串,利用字符串的下标和中括号“[]”可以访问指定索引位置的字符,并对该字符进行读写,语法“字符串名[下标值]”;字符串的下标值(索引值)只能是整数类型,起始值为0。

在PHP中,可以利用implode()函数的第一个参数来设置没有分隔符,该函数的第一个参数用于规定数组元素之间放置的内容,默认是空字符串,也可将第一个参数设置为空,语法为“implode(数组)”或者“implode("",数组)”。


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