行为型模式 --- 备忘录模式

package study.org;

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

public class Demo {
    public static void main(String[] args) {
        Model originator = new Model();
        Storage storage = new Storage();

        originator.setValue("State #1"); // first init value
        storage.add(originator.saveStateToMemento());

        originator.setValue("State #2");// second init value
        storage.add(originator.saveStateToMemento());

        System.out.println("Current State: " + originator.getValue());
        originator.restoreMemento(storage.get(0));
        System.out.println("First saved State: " + originator.getValue());
        originator.restoreMemento(storage.get(1));
        System.out.println("Second saved State: " + originator.getValue());
    }
}

// 备忘
class Memento {
    private String state;

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

    public String getState() {
        return state;
    }
}

// 测试实体类
class Model {
    private String value;

    public String getValue() {
        return value;
    }

    public void setValue(String value) {
        this.value = value;
    }

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

    public void restoreMemento(Memento memento) {
        this.value = memento.getState();
    }
}

// 存储
class Storage {
    private List<Memento> mementoList = new ArrayList<Memento>();

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

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