14-备忘录模式

14-备忘录模式

概念

备忘录模式（Memento）:在不破坏封装性的前提下，捕获一个对象的内部状态，并在改对象之外保存这个状态，这样以后就可将改对象回复到原先保存的状态

适用情况

Memento模式比较适用于功能比较复杂的，但需要维护或记录属性历史的类，或者需要保存的属性只是众多属性中的一肖部分时，发起者（Originator）可以根据保存的Memento信息还原到前一状态。常见的使用场景是游戏进度存储。

实践

以下是书中游戏状态存储的例子

package com.gof.memento;

/**
 * 功能描述
 *
 * @since 2023-02-03
 */
public class GameRole {
    // 生命力
    private int vitality;

    // 攻击力
    private int attack;

    // 防御力
    private int defense;

    public void initGameRole() {
        vitality = 100;
        attack = 100;
        defense = 100;
    }

    public void fight() {
        vitality = 0;
        attack = 0;
        defense = 0;
    }

    public void displayState() {
        System.out.println(String.format("vitality: %d", vitality));
        System.out.println(String.format("attack: %d", attack));
        System.out.println(String.format("defense: %d", defense));
    }

    public GameRoleStateMemento createMemento() {
        return new GameRoleStateMemento(vitality, attack, defense);
    }

    public void setMemento(GameRoleStateMemento m) {
        vitality = m.getVitality();
        attack = m.getAttack();
        defense = m.getDefense();
    }

    public int getVitality() {
        return vitality;
    }

    public void setVitality(int vitality) {
        this.vitality = vitality;
    }

    public int getAttack() {
        return attack;
    }

    public void setAttack(int attack) {
        this.attack = attack;
    }

    public int getDefense() {
        return defense;
    }

    public void setDefense(int defense) {
        this.defense = defense;
    }
}

package com.gof.memento;

/**
 * 功能描述
 *
 * @since 2023-02-03
 */
public class GameRoleStateMemento {
    private int vitality;

    private int attack;

    private int defense;

    public GameRoleStateMemento() {
    }

    public GameRoleStateMemento(int vitality, int attack, int defense) {
        this.vitality = vitality;
        this.attack = attack;
        this.defense = defense;
    }

    public int getVitality() {
        return vitality;
    }

    public void setVitality(int vitality) {
        this.vitality = vitality;
    }

    public int getAttack() {
        return attack;
    }

    public void setAttack(int attack) {
        this.attack = attack;
    }

    public int getDefense() {
        return defense;
    }

    public void setDefense(int defense) {
        this.defense = defense;
    }
}

package com.gof.memento;

/**
 * 功能描述
 *
 * @since 2023-02-03
 */
public class RoleStateCareTaker {
    private GameRoleStateMemento memento;

    public RoleStateCareTaker() {
    }

    public RoleStateCareTaker(GameRoleStateMemento memento) {
        this.memento = memento;
    }

    public GameRoleStateMemento getMemento() {
        return memento;
    }

    public void setMemento(GameRoleStateMemento memento) {
        this.memento = memento;
    }
}

package com.gof.memento;

/**
 * 功能描述
 *
 * @since 2023-02-03
 */
public class Client {
    public static void main(String[] args) {
        GameRole role = new GameRole();
        role.initGameRole();
        role.displayState();

        RoleStateCareTaker careTaker = new RoleStateCareTaker();

        careTaker.setMemento(role.createMemento());
        role.fight();
        role.displayState();

        role.setMemento(careTaker.getMemento());
        role.displayState();

    }
}