备忘录模式

简介

备忘录模式（Memento Pattern）保存一个对象的某个状态，以便在适当的时候恢复对象。备忘录模式属于行为型模式。

实现

1. 创建Memento类

public class Memento {
    private String state;

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

    public String getState(){
        return state;
    }
}

2. 创建Originator类

public class Originator {
    private String state;

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

    public String getState(){
        return state;
    }

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

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

3. 创建CareTaker类

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);
    }
}

4. 使用CareTaker和Originator对象

public class MementoPatternDemo {
    public static void main(String[] args) {
        Originator originator = new Originator();
        CareTaker careTaker = new CareTaker();

        originator.setState("状态1");
        originator.setState("状态2");

        careTaker.add(originator.saveStateToMemento());
        originator.setState("状态3");
        careTaker.add(originator.saveStateToMemento());
        originator.setState("状态4");

        System.out.println("当前状态: "+originator.getState());
        originator.getStateFromMemento(careTaker.get(0));
        System.out.println("第一个状态: " + originator.getState());
        originator.getStateFromMemento(careTaker.get(1));
        System.out.println("第二个状态: " + originator.getState());
    }
}

类图

代码

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