目录

前言

UML

plantuml

类图

实战代码

模板

Originator

Memento

CareTaker

Client

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前言

使用备忘录模式，主要目的就是创建对象副本，保存对象内部状态的的快照，以便在需要时恢复对象至某一个历史状态。

仅仅从创建副本来看，备忘录模式和原型模式其实没啥区别，不过备忘录模式是行为型设计模式，重点在于恢复对象到某一历史状态。

备忘录模式下，总共有三个角色，原始对象 Originator，对象快照 Memento，以及管理它们的 CareTaker

UML

plantuml

@startuml
'https://plantuml.com/class-diagramclass Originator {- attr : type+ createMemento() : Memento+ restore(Memento) : void
}class Memento {- attr : type
}class CareTaker {- originator : Originator- mementos : List<Memento>+ createMemento() : void+ restore(int) : void
}class Client {}Originator ..> Memento
CareTaker "1" --> "1" Originator
CareTaker "1" --> "n" MementoClient -->  CareTaker
Client -->  Originator@enduml

类图

实战代码

模板

Originator

class Originator {String state;Originator(String state) {this.state = state;}public String getState() {return state;}public void setState(String state) {this.state = state;}public Memento createMemento() {Memento memento = new Memento();memento.setState(this.state);return memento;}public void restore(Memento memento) {this.state = memento.getState();}
}

Memento

public class Memento {private String state;public String getState() {return state;}public void setState(String state) {this.state = state;}
}

CareTaker

class CareTaker {Originator originator;List<Memento> mementos;CareTaker(Originator originator) {this.originator = originator;mementos = new ArrayList<>();}public void createMemento() {Memento memento = this.originator.createMemento();mementos.add(memento);}public void restore(int index) {this.originator.restore(mementos.get(index));}
}

Client

public class Client {public static void main(String[] args) {Originator originator = new Originator("init");CareTaker careTaker = new CareTaker(originator);System.out.println(originator.getState());careTaker.createMemento();originator.setState("run");careTaker.createMemento();System.out.println(originator.getState());careTaker.restore(0);System.out.println(originator.getState());}
}