举动型模式-备忘录模式（Memento）

行为型模式--备忘录模式（Memento）

Original类是原始类，里面有需要保存的属性value及创建一个备忘录类，用来保存value值。Memento类是备忘录类，Storage类是存储备忘录的类，持有Memento类的实例，该模式很好理解。直接看源码：

[java]?view plaincopy

1. public?class?Original?{??
2. ??????
3. ????private?String?value;??
4. ??????
5. ????public?String?getValue()?{??
6. ????????return?value;??
7. ????}??
8. ??
9. ????public?void?setValue(String?value)?{??
10. ????????this.value?=?value;??
11. ????}??
12. ??
13. ????public?Original(String?value)?{??
14. ????????this.value?=?value;??
15. ????}??
16. ??
17. ????public?Memento?createMemento(){??
18. ????????return?new?Memento(value);??
19. ????}??
20. ??????
21. ????public?void?restoreMemento(Memento?memento){??
22. ????????this.value?=?memento.getValue();??
23. ????}??
24. }??

[java]?view plaincopy

1. public?class?Memento?{??
2. ??????
3. ????private?String?value;??
4. ??
5. ????public?Memento(String?value)?{??
6. ????????this.value?=?value;??
7. ????}??
8. ??
9. ????public?String?getValue()?{??
10. ????????return?value;??
11. ????}??
12. ??
13. ????public?void?setValue(String?value)?{??
14. ????????this.value?=?value;??
15. ????}??
16. }??

[java]?view plaincopy

1. public?class?Storage?{??
2. ??????
3. ????private?Memento?memento;??
4. ??????
5. ????public?Storage(Memento?memento)?{??
6. ????????this.memento?=?memento;??
7. ????}??
8. ??
9. ????public?Memento?getMemento()?{??
10. ????????return?memento;??
11. ????}??
12. ??
13. ????public?void?setMemento(Memento?memento)?{??
14. ????????this.memento?=?memento;??
15. ????}??
16. }??

测试类：

[java]?view plaincopy

1. public?class?Test?{??
2. ??
3. ????public?static?void?main(String[]?args)?{??
4. ??????????
5. ????????//?创建原始类??
6. ????????Original?origi?=?new?Original("egg");??
7. ??
8. ????????//?创建备忘录??
9. ????????Storage?storage?=?new?Storage(origi.createMemento());??
10. ??
11. ????????//?修改原始类的状态??
12. ????????System.out.println("初始化状态为："?+?origi.getValue());??
13. ????????origi.setValue("niu");??
14. ????????System.out.println("修改后的状态为："?+?origi.getValue());??
15. ??
16. ????????//?回复原始类的状态??
17. ????????origi.restoreMemento(storage.getMemento());??
18. ????????System.out.println("恢复后的状态为："?+?origi.getValue());??
19. ????}??
20. }??

输出：

初始化状态为：egg
修改后的状态为：niu
恢复后的状态为：egg

简单描述下：新建原始类时，value被初始化为egg，后经过修改，将value的值置为niu，最后倒数第二行进行恢复状态，结果成功恢复了。其实我觉得这个模式叫“备份-恢复”模式最形象。

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