设计模式读书笔记之备忘录模式(Memento)

备忘录模式：在不破坏封装性的前提下，捕获对象的内部状态并保存，这样以后就可以恢复该对象恢复到保存的状态。

备忘录模式比较简单,　不要因为名字比较陌生而不敢学它.　它没有复杂的结构,　上图已经能足够说明问题.

Originator: 备忘录发起人,　通常是需要备忘的对象自己.

Memento: 备忘录对象, 保存了Originator的内部状态.

CareTaker: 备忘录管理者.

基本代码：

//备忘录发起人，即需要备忘的对象 package designpattern.memento; public class Originator { private String state; public String getState() { return state; } public void setState(String state) { this.state = state; } public Memento createMemo(){ return new Memento(state); } public void recover(Memento m){ this.state = m.getState(); } public void show(){ System.out.println("state = " + state); } } //备忘录 package designpattern.memento; public class Memento { private String state; public String getState() { return state; } public Memento(String state){ this.state = state; } } //备忘录管理者 package designpattern.memento; public class CareTaker { private Memento memento; public Memento getMemento() { return memento; } public void setMemento(Memento memento) { this.memento = memento; } } //test case package designpattern.memento; public class Test { public static void main(String[] args) { Originator o = new Originator(); o.setState("On"); o.show(); CareTaker c = new CareTaker(); c.setMemento(o.createMemo()); o.setState("Off"); o.show(); o.recover(c.getMemento()); o.show(); } }

举例：

打rpg游戏的时候经常在打大boss之前把游戏保存一下，如果死了，就重新来。其实这就是备忘录模式。看代码：

package designpattern.memento.game; public class GameRole { private int vitality; private int attack; private int defense; public GameRole(){ this.vitality = 100; this.attack = 100; this.defense = 100; } public void showState(){ System.out.println("vitality = " + vitality + "/nattack = " + attack + "/ndefence = " + defense); } public RoleStateMemo save(){ return new RoleStateMemo(vitality, attack, defense); } public void recover(RoleStateMemo m){ System.out.println("太菜了我，还好我存盘了，哈哈。"); System.out.println("复活中......"); this.vitality = m.getVitality(); this.attack = m.getAttack(); this.defense = m.getDefense(); System.out.println("又复活了."); } public void fight(){ System.out.println("与大Boss决战./n......"); System.out.println("你输了, 你的生命，防御, 战斗力都将减为0."); this.vitality = 0; this.defense = 0; this.attack = 0; } } // package designpattern.memento.game; public class RoleStateMemo { private int vitality; private int attack; private int defense; public RoleStateMemo(int v, int a, int d){ this.vitality = v; this.attack = a; this.defense = d; } public int getVitality() { return vitality; } public void setVitality(int vitality) { this.vitality = vitality; } public int getAttack() { return attack; } public void setAttack(int attack) { this.attack = attack; } public int getDefense() { return defense; } public void setDefense(int defense) { this.defense = defense; } } // package designpattern.memento.game; public class RoleMemoManager { private RoleStateMemo m; public RoleStateMemo getM() { return m; } public void setM(RoleStateMemo m) { this.m = m; } } //test case package designpattern.memento.game; public class Test { public static void main(String[] args) { GameRole role = new GameRole(); role.showState(); RoleMemoManager manager = new RoleMemoManager(); manager.setM(role.save()); role.fight(); role.showState(); role.recover(manager.getM()); role.showState(); } }

适用情景：

需要维护或记录历史的类。