设计模式——备忘录模式

备忘录模式是什么？

在不破坏封装性的前提下，捕获一个对的内部状态，并在该对象之外保持这个状态。这样以后就可将该对象恢复到原先保持的状态

备忘录模式解决什么问题？

如游戏打Boss失败时回档，定义一个游戏角色

public class GameRole {
    private int vitality;
    private int attack;
    private int 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;
    }
    public void displayState() {
        System.out.println("角色当前状态：");
        System.out.println("体力：" + vitality);
        System.out.println("攻击力：" + attack);
        System.out.println("防御力：" + defense);
    }
    public void getInitState() {
        vitality = 100;
        attack = 100;
        defense = 100;
    }
    public void fight() {
        vitality = 0;
        attack = 0;
        defense = 0;
    }
}
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在挑战Boss前，复制一份当前的状态

GameRole role = new GameRole();
role.getInitState();
role.displayState();

GameRole backup = new GameRole();
backup.setVitality(role.getVitality());
backup.setAttack(role.getAttack());
backup.setDefense(role.getDefense());
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当挑战Boss失败后，通过此前的复制还原状态

role.fight();
role.displayState();

role.setVitality(backup.getVitality());
role.setAttack(backup.getAttack());
role.setDefense(backup.getDefense());
role.displayState();
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• problem1：需要对属性一个个进行备份
• problem2：当属性增加或修改时，需要对代码修改

备忘录模式实现

创建备忘录，添加要保存的数据

public class RoleStateMemento {
    private int vitality;
    private int attack;
    private int defense;

    public RoleStateMemento(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;
    }
}
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修改GameRole类，添加备份/还原方法

public class GameRole {
    private int vitality;
    private int attack;
    private int 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;
    }

    public void displayState() {
        System.out.println("角色当前状态：");
        System.out.println("体力：" + vitality);
        System.out.println("攻击力：" + attack);
        System.out.println("防御力：" + defense);
    }

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

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

    public RoleStateMemento saveState() {
        return new RoleStateMemento(vitality, attack, defense);
    }

    public void recoveryState(RoleStateMemento memento) {
        vitality = memento.getVitality();
        attack = memento.getAttack();
        defense = memento.getDefense();
    }
}
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创建它们之间的管理类

public class RoleStateCaretaker {
    private RoleStateMemento mMemento;

    public RoleStateMemento getMemento() {
        return mMemento;
    }

    public void setMemento(RoleStateMemento memento) {
        mMemento = memento;
    }
}
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备份/还原代码如下

GameRole role = new GameRole();
role.getInitState();
role.displayState();

RoleStateCaretaker stateCaretaker = new RoleStateCaretaker();
stateCaretaker.setMemento(role.saveState());

role.fight();
role.displayState();

role.recoveryState(stateCaretaker.getMemento());
role.displayState();
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