设计模式学习—备忘录模式(Memento Design Pattern)

一、我的理解

备忘录模式用于存储某个类在某一时刻的状态。

二、实现方式

另外创建一个类Memento用于保存目标类的状态信息，然后由另一类来存储和管理这一系列保存的状态

三、实例

Java实例
Originator类：原始类，对该类的状态进行保存

package com.study.dp.memento;

public class Originator {

private String state;

public String getState() {
return state;
}

public void setState(String state) {
this.state = state;
}

public Memento saveStateToMemento() {
return new Memento(state);
}

public void getStateFromMemento(Memento memento) {
this.state = memento.getState();
}

}

Memento类：备忘录类，保存目标类的状态信息

package com.study.dp.memento;

public class Memento {

private String state;

public Memento(String state) {
super();
this.state = state;
}

public String getState() {
return state;
}

}

CareTaker类：备忘录管理类，存储和管理备忘录

package com.study.dp.memento;

import java.util.ArrayList;
import java.util.List;

public class CareTaker {

private List<Memento> mementoList = new ArrayList<>();

public void add(Memento state) {
mementoList.add(state);
}

public Memento get(int index) {
return mementoList.get(index);
}

}

Demo类：测试

package com.study.dp.memento;

public class Demo {

public static void main(String[] args) {
Originator originator = new Originator();
CareTaker careTaker = new CareTaker();
originator.setState("State #1");
originator.setState("State #2");
careTaker.add(originator.saveStateToMemento());
originator.setState("State #3");
careTaker.add(originator.saveStateToMemento());
originator.setState("State #4");

System.out.println("Current State: "+originator.getState());
originator.getStateFromMemento(careTaker.get(0));
System.out.println("First saved State: "+originator.getState());
originator.getStateFromMemento(careTaker.get(1));
System.out.println("Second saved State: "+originator.getState());
}

}

四、应用场景