25 行为型模式-备忘录模式

1 备忘录模式介绍

备忘录模式(memento pattern)定义: 在不破坏封装的前提下,捕获一个对象的内部状态,并在该对象之外保存这个状态,这样可以在以后将对象恢复到原先保存的状态.

2 备忘录模式原理

3 备忘录模式实现

/*** 发起人角色**/
public class Originator {private String state = "原始对象";private String id;private String name;private String phone;public Originator() {}//创建备忘录对象public Memento createMemento(){return new Memento(id,name,phone);}//恢复对象public void restoreMemento(Memento m){this.state = m.getState();this.id = m.getId();this.name = m.getName();this.phone = m.getPhone();}@Overridepublic String toString() {return "Originator{" +"state='" + state + '\'' +", id='" + id + '\'' +", name='" + name + '\'' +", phone='" + phone + '\'' +'}';}public String getState() {return state;}public void setState(String state) {this.state = state;}public String getId() {return id;}public void setId(String id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getPhone() {return phone;}public void setPhone(String phone) {this.phone = phone;}
}

/*** 备忘录角色* 访问权限为: 默认,在同包下可见(尽量保证只有发起者类可以访问备忘录类)**/
class Memento {private String state = "从备份对象恢复原始对象";private String id;private String name;private String phone;public Memento() {}public Memento(String id, String name, String phone) {this.id = id;this.name = name;this.phone = phone;}public String getState() {return state;}public void setState(String state) {this.state = state;}public String getId() {return id;}public void setId(String id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getPhone() {return phone;}public void setPhone(String phone) {this.phone = phone;}@Overridepublic String toString() {return "Memento{" +"state='" + state + '\'' +", id='" + id + '\'' +", name='" + name + '\'' +", phone='" + phone + '\'' +'}';}
}

/*** 负责人类-获取和保存备忘录对象**/
public class Caretaker {private Memento memento;public Memento getMemento() {return memento;}public void setMemento(Memento memento) {this.memento = memento;}
}

public class Client {public static void main(String[] args) {//创建发起人对象Originator o1 = new Originator();o1.setId("1");o1.setName("spike");o1.setPhone("13522777722");System.out.println("========"+o1);//创建负责人对象Caretaker caretaker = new Caretaker();caretaker.setMemento(o1.createMemento());//修改o1.setName("update");System.out.println("========" + o1);//从负责人对象中获取备忘录对象,实现恢复操作o1.restoreMemento(caretaker.getMemento());System.out.println("========" + o1);}
}

4 备忘录模式应用实例

/*** 备份玩家的状态**/
class Memento {private int money;  //玩家获取的金币ArrayList fruits;  //玩家获取的水果public Memento(int money) {this.money = money;this.fruits = new ArrayList();}//获取当前玩家的金币public int getMoney(){return money;}//获取当前玩家的水果List getFruits(){return (List) fruits.clone();}//添加水果void addFruit(String fruit){fruits.add(fruit);}}

Player玩家类,只要玩家的金币还够,就会一直进行游戏,在该类中会设置一个createMemento方法,其作用是保存当前玩家状态.还会包含一个restore撤销方法,相当于复活操作.

/*** 玩家类**/
public class Player {private int money;  //金币private List<String> fruits = new ArrayList<>();  //玩家获得的水果private static String[] fruitsName ={   //表示水果种类的数组"苹果","葡萄","香蕉","橘子"};Random random = new Random();public Player(int money) {this.money = money;}//获取当前所有金币public int getMoney(){return money;}//获取一个水果public String getFruit(){String prefix = "";if(random.nextBoolean()){prefix = "好吃的";}//从数组中拿一个水果String f = fruitsName[random.nextInt(fruitsName.length)];return prefix + f;}//掷骰子方法public void yacht(){int dice = random.nextInt(6) + 1; //掷骰子if(dice == 1){money += 100;System.out.println("所持有的金币增加了...");}else if(dice == 2){money /= 2;System.out.println("所持有的金币减少一半");}else if(dice == 6){ //获取水果String fruit = getFruit();System.out.println("获取了水果: " + fruit);fruits.add(fruit);}else{//其他结果System.out.println("无效数字,继续投掷!");}}//拍摄快照public Memento createMemento(){Memento memento = new Memento(money);for (String fruit : fruits) {//判断: 只保存 '好吃的'水果if(fruit.startsWith("好吃的")){memento.addFruit(fruit);}}return memento;}//撤销方法public void restoreMemento(Memento memento){this.money = memento.getMoney();this.fruits = memento.getFruits();}@Overridepublic String toString() {return "Player{" +"money=" + money +", fruits=" + fruits +'}';}
}

测试: 由于引入了备忘录模式,可以保存某个时间点的玩家状态,这样就可以对玩家进行复活操作.

public class MainApp {public static void main(String[] args) throws InterruptedException {//创建玩家类,设置初始金币Player player = new Player(100);//创建备忘录对象Memento memento = player.createMemento();for (int i = 0; i < 100; i++) {//显示扔骰子的次数System.out.println("第" + i+"次投掷!");//显示当前玩家状态System.out.println("当前状态: " + player);//开启游戏player.yacht();System.out.println("玩家所持有的金币: " + player.getMoney() + " 元");//复活操作if(player.getMoney() > memento.getMoney()){System.out.println("赚到金币,保存当前状态,继续游戏!");memento = player.createMemento();  //更新快照}else if(player.getMoney() < memento.getMoney() / 2){System.out.println("所持金币不多,将游戏恢复到初始状态!");player.restoreMemento(memento);}Thread.sleep(1000);}}
}

5 备忘录模式总结