十八、备忘录模式——SL大法，读档的实现-优快云博客

文章目录

备忘录模式
总结

设计模式是面向问题、场景而总结产生的设计思路。是解决问题的套路。23 种经典的设计模式。它们又可以分为三大类：创建型、结构型、行为型。

行为型包含了观察者模式、模板模式、策略模式、职责链模式、状态模式、迭代器模式、访问者模式、备忘录模式、命令模式、解释器模式、中介模式总共11种模式。

备忘录模式

很多时候我们总是需要记录一个对象的内部状态，这样做的目的就是为了允许用户取消不确定或者错误的操作，能够恢复到他原先的状态，使得他有"后悔药"可吃。为了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。这样可以在以后将对象恢复到原先保存的状态。解决办法是，通过一个备忘录类专门存储对象状态。Windows 里的 ctrl + z 、数据库的事务管理、数据库备份与还原、编辑器撤销与重做、虚拟机生成快照与恢复、Git版本管理、棋牌游戏悔棋都是备忘录模式的应用。

以游戏存档为例，可以多次存档，并挑选存档读档。存档时记录血量、魔法值已经所属地图。

1. Snapshot 存档

Snapshot 记录当时游戏状态。

public class Snapshot {
    private int health;
    private int magic;
    private String town;

    public Snapshot(int health, int magic, String town) {
        this.health = health;
        this.magic = magic;
        this.town = town;
    }

    public int getHealth() {
        return health;
    }

    public void setHealth(int health) {
        this.health = health;
    }

    public int getMagic() {
        return magic;
    }

    public void setMagic(int magic) {
        this.magic = magic;
    }

    public String getTown() {
        return town;
    }

    public void setTown(String town) {
        this.town = town;
    }
}

2. SnapshotHolder 存档列表

内部持有存档列表snapshotList ，对存档进行管理。

public class SnapshotHolder {
    private List<Snapshot> snapshotList = new ArrayList<>();

    public boolean addSnapShot(Snapshot snapshot) {
        return snapshotList.add(snapshot);
    }

    public Snapshot getSnapShot(int index) {
        return snapshotList.get(index);
    }
}

3. Game 游戏

Game提供存档和读档功能。其主要功能是存档和读档。

public class Game {

    private int health;
    private int magic;
    private String town;

    public Game(int health, int magic, String town) {
        this.health = health;
        this.magic = magic;
        this.town = town;
    }

    public Snapshot save(){
        return new Snapshot(health,magic,town);
    }

    public void restore(Snapshot snapshot) {
        this.health = snapshot.getHealth();
        this.magic = snapshot.getMagic();
        this.town = snapshot.getTown();
    }

    public void setHealth(int health) {
        this.health = health;
    }

    public void setMagic(int magic) {
        this.magic = magic;
    }

    public void setTown(String town) {
        this.town = town;
    }

    @Override
    public String toString() {
        return "Game{" +
                "health=" + health +
                ", magic=" + magic +
                ", town='" + town + '\'' +
                '}';
    }
}

4. Main 组合运行

多次存档并选择回到第一次状态。

public class Main {

    public static void main(String[] args) {
        SnapshotHolder snapshotHolder = new SnapshotHolder();
        Game game = new Game(100,210,"五蛇殿");
        snapshotHolder.addSnapShot(game.save());
        System.out.println("当前game state:"+game);

        game.setHealth(80);
        game.setMagic(20);
        game.setTown("土城");
        snapshotHolder.addSnapShot(game.save());
        System.out.println("当前game state:"+game);

        game.setHealth(100);
        game.setMagic(50);
        game.setTown("机关洞");
        snapshotHolder.addSnapShot(game.save());
        System.out.println("当前game state:"+game);

        game.restore(snapshotHolder.getSnapShot(0));
        System.out.println("读档后:game state:"+game);
    }
}

运行结果：

当前game state:Game{health=100, magic=210, town='五蛇殿'}
当前game state:Game{health=80, magic=20, town='土城'}
当前game state:Game{health=100, magic=50, town='机关洞'}
读档后:game state:Game{health=100, magic=210, town='五蛇殿'}