备忘录模式 (Memento Pattern)

1、类图

2、代码

import java.util.ArrayList;

public class Main {
    
    public static void main(String[] args) {
        Originator originator = new Originator();
        CareTaker careTaker = new CareTaker();
        
        originator.setMessage("记下第一件事：吃饭");
        careTaker.saveMemento(originator.createMemento());  // 保存进备忘录
        originator.setMessage("记下第二件事：睡觉");
        careTaker.saveMemento(originator.createMemento());
        originator.restoreMemento(careTaker.getMementoByIdx(0));  // 载入备忘录信息
        System.out.println(originator.getMessage());
    }

}

class Memento {

    private String message = null;

    public Memento(String message) {
        this.message = message;
    }

    public String getMessage() {
        return message;
    }

}

class Originator {

    private String message = null;

    public String getMessage() {
        return message;
    }
    public void setMessage(String message) {
        this.message = message;
    }

    public Memento createMemento() {
        return new Memento(this.message);
    }
    public void restoreMemento(Memento memento) {
        this.setMessage(memento.getMessage());
    }

}

class CareTaker {

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

    public void saveMemento(Memento memento) {
        mementoList.add(memento);
    }

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

}