备忘录模式——对象行为型模式

一、意图
在不破坏封装性的前提下，捕获一个对象的内部状态，并在该对象之外保存这个状态。这样以后就可以将该对象恢复到原先保存的状态。
二、适用性
以下情况使用备忘录模式：

• 必须保存一个对象在某一时刻的（部分）状态，这样以后需要时它才能恢复到先前的状态。
• 如果一个用接口来让其它对象直接取得这些状态，将会暴露对象的实现细节并破坏对象的封装性。

三、结构

四、代码

public class CallOfDuty {
    private int mCheckpoint = 1;
    private int mLifeValue = 100;
    private String mWeapon = "沙漠之鹰";

    public void play() {
        System.out.println("玩游戏: " + String.format("第%d关", mCheckpoint) + "奋战杀敌中");
        mLifeValue -= 10;
        System.out.println("进度升级啦");
        mCheckpoint++;
        System.out.println("到达 " + String.format("第%d关", mCheckpoint));
    }

    public void quit() {
        System.out.println("-----------------");
        System.out.println("退出前游戏属性: " + this.toString());
        System.out.println("退出游戏");
        System.out.println("-----------------");

    }

    public Memento createMemento() {
        Memento memento = new Memento();
        memento.mCheckPoint = this.mCheckpoint;
        memento.mLifeValue = this.mLifeValue;
        memento.mWeapon = this.mWeapon;
        return memento;
    }

    public void restore(Memento memento){
        this.mCheckpoint =memento.mCheckPoint;
        this.mLifeValue = memento.mLifeValue;
        this.mWeapon = memento.mWeapon;

        System.out.println("恢复后的游戏属性: "+this.toString());
    }

    @Override
    public String toString() {
        return "CallOfDuty{" +
                "mCheckpoint=" + mCheckpoint +
                ", mLifeValue=" + mLifeValue +
                ", mWeapon='" + mWeapon + '\'' +
                '}';
    }
}

public class Memento {
    public int mCheckPoint;
    public int mLifeValue;
    public String mWeapon;

    @Override
    public String toString() {
        return "Memento{" +
                "mCheckPoint=" + mCheckPoint +
                ", mLifeValue=" + mLifeValue +
                ", mWeapon='" + mWeapon + '\'' +
                '}';
    }
}

public class Caretaker {
    Memento memento;

    public void archive(Memento memento){
        this.memento = memento;
    }

    public Memento getMemento(){
        return memento;
    }
}

public class Client {

    public static void main(String[] args){
        // 构建游戏对象
        CallOfDuty game = new CallOfDuty();
        game.play();
        Caretaker caretaker = new Caretaker();
        caretaker.archive(game.createMemento());
        game.quit();

        CallOfDuty newGame = new CallOfDuty();
        newGame.restore(caretaker.memento);

    }
}