Java中的模式 --
一、定义：备忘录(memento)模式又叫快照(snapshot)模式或者token模式，主要功能：备忘录模式是用一个对象来存储另外一个对象的内部状态的快照，实现备忘录模式的关键点是在不破坏封装的
情况下，将一个对象的状态捕捉住，并外部化，存储起来，从而可以在合适的时候，把这个对象还原。
说明：备忘录模式适模式中比较好理解的一个，这里就不举例子，但是备忘录模式是模式中实现比较难，或者说
实现比较巧的，这里主要说说。
二、备忘录模式的实现
1,备忘录模式中的角色
发起人：创建含有内部状态的备忘录对象，并使用备忘录对象存储状态
负责人：负责人保存备忘录对象，但不检查备忘录对象的内容
备忘录：备忘录对象将发起人对象的内部状态存起来，并保正其内容不被发起人对象之外的对象像读取
注意：在备忘录的角色中，定义了他必须对不同的人提供不同的接口，对发起人提供宽接口，对其它任何人提供窄
接口。也许你说我都提供宽接口得了。对这也是备忘录的一种实现，叫做白箱备忘录，不过这种方法的封装没有设计
好，安全性不够好。
2,白箱备忘录的实现：
<div style="border-right: #cccccc 1px solid; padding-right: 5px; border-top: #cccccc 1px solid; padding-left: 4px; font-size: 13px; padding-bottom: 4px; border-left: #cccccc 1px solid; width: 98%; padding-top: 4px; border-bottom: #cccccc 1px solid; background-color: #eeeeee;"> 1http://www.agoit.com/Images/OutliningIndicators/ExpandedBlockStart.gifhttp://www.agoit.com/Images/OutliningIndicators/ContractedBlock.gifpublic class Originatorhttp://www.agoit.com/Images/dot.gif{
2http://www.agoit.com/Images/OutliningIndicators/InBlock.gif private String state;
3http://www.agoit.com/Images/OutliningIndicators/ExpandedSubBlockStart.gifhttp://www.agoit.com/Images/OutliningIndicators/ContractedSubBlock.gif public Memento CreateMemento()http://www.agoit.com/Images/dot.gif{
4http://www.agoit.com/Images/OutliningIndicators/InBlock.gif return new Memento(state);
5http://www.agoit.com/Images/OutliningIndicators/ExpandedSubBlockEnd.gif }
6http://www.agoit.com/Images/OutliningIndicators/ExpandedSubBlockStart.gifhttp://www.agoit.com/Images/OutliningIndicators/ContractedSubBlock.gif public void restoreMemento(Memento memento)http://www.agoit.com/Images/dot.gif{
7http://www.agoit.com/Images/OutliningIndicators/InBlock.gif this.state = memento.getState();
8http://www.agoit.com/Images/OutliningIndicators/ExpandedSubBlockEnd.gif }
9http://www.agoit.com/Images/OutliningIndicators/ExpandedSubBlockStart.gifhttp://www.agoit.com/Images/OutliningIndicators/ContractedSubBlock.gif public String getState()http://www.agoit.com/Images/dot.gif{
10http://www.agoit.com/Images/OutliningIndicators/InBlock.gif return this.state;
11http://www.agoit.com/Images/OutliningIndicators/ExpandedSubBlockEnd.gif }
12http://www.agoit.com/Images/OutliningIndicators/ExpandedSubBlockStart.gifhttp://www.agoit.com/Images/OutliningIndicators/ContractedSubBlock.gif public void setState(String state)http://www.agoit.com/Images/dot.gif{
13http://www.agoit.com/Images/OutliningIndicators/InBlock.gif this.state=state;
14http://www.agoit.com/Images/OutliningIndicators/InBlock.gif System.out.println("Current state = " + this.state);
15http://www.agoit.com/Images/OutliningIndicators/ExpandedSubBlockEnd.gif }
16http://www.agoit.com/Images/OutliningIndicators/ExpandedBlockEnd.gif}
17http://www.agoit.com/Images/OutliningIndicators/ExpandedBlockStart.gifhttp://www.agoit.com/Images/OutliningIndicators/ContractedBlock.gifpublic class Mementohttp://www.agoit.com/Images/dot.gif{
18http://www.agoit.com/Images/OutliningIndicators/InBlock.gif private String state;
19http://www.agoit.com/Images/OutliningIndicators/ExpandedSubBlockStart.gifhttp://www.agoit.com/Images/OutliningIndicators/ContractedSubBlock.gif public Memento(String state)http://www.agoit.com/Images/dot.gif{
20http://www.agoit.com/Images/OutliningIndicators/InBlock.gif this.state = state;
21http://www.agoit.com/Images/OutliningIndicators/ExpandedSubBlockEnd.gif }
22http://www.agoit.com/Images/OutliningIndicators/ExpandedSubBlockStart.gifhttp://www.agoit.com/Images/OutliningIndicators/ContractedSubBlock.gif public String getState()http://www.agoit.com/Images/dot.gif{
23http://www.agoit.com/Images/OutliningIndicators/InBlock.gif return this.state;
24http://www.agoit.com/Images/OutliningIndicators/ExpandedSubBlockEnd.gif }
25http://www.agoit.com/Images/OutliningIndicators/ExpandedSubBlockStart.gifhttp://www.agoit.com/Images/OutliningIndicators/ContractedSubBlock.gif public void setState()http://www.agoit.com/Images/dot.gif{
26http://www.agoit.com/Images/OutliningIndicators/InBlock.gif this.state = state;
27http://www.agoit.com/Images/OutliningIndicators/ExpandedSubBlockEnd.gif }
28http://www.agoit.com/Images/OutliningIndicators/ExpandedBlockEnd.gif}
29http://www.agoit.com/Images/OutliningIndicators/ExpandedBlockStart.gifhttp://www.agoit.com/Images/OutliningIndicators/ContractedBlock.gifpublic class Caretakerhttp://www.agoit.com/Images/dot.gif{
30http://www.agoit.com/Images/OutliningIndicators/InBlock.gif private Memento memento;
31http://www.agoit.com/Images/OutliningIndicators/ExpandedSubBlockStart.gifhttp://www.agoit.com/Images/OutliningIndicators/ContractedSubBlock.gif public Memento retrieveMemento()http://www.agoit.com/Images/dot.gif{
32http://www.agoit.com/Images/OutliningIndicators/InBlock.gif return this.memento;
33http://www.agoit.com/Images/OutliningIndicators/ExpandedSubBlockEnd.gif }
34http://www.agoit.com/Images/OutliningIndicators/ExpandedSubBlockStart.gifhttp://www.agoit.com/Images/OutliningIndicators/ContractedSubBlock.gif public void saveMemento(Memento memento)http://www.agoit.com/Images/dot.gif{
35http://www.agoit.com/Images/OutliningIndicators/InBlock.gif this.memento = memento;
36http://www.agoit.com/Images/OutliningIndicators/ExpandedSubBlockEnd.gif }
37http://www.agoit.com/Images/OutliningIndicators/ExpandedBlockEnd.gif}
38http://www.agoit.com/Images/OutliningIndicators/ExpandedBlockStart.gifhttp://www.agoit.com/Images/OutliningIndicators/ContractedBlock.gifpublic class Clienthttp://www.agoit.com/Images/dot.gif{
39http://www.agoit.com/Images/OutliningIndicators/InBlock.gif private static Originator o = new Originator();
40http://www.agoit.com/Images/OutliningIndicators/InBlock.gif private static Caretaker c = new Caretaker();
41http://www.agoit.com/Images/OutliningIndicators/ExpandedSubBlockStart.gifhttp://www.agoit.com/Images/OutliningIndicators/ContractedSubBlock.gif public static void main(Sting[] args)http://www.agoit.com/Images/dot.gif{
42http://www.agoit.com/Images/OutliningIndicators/InBlock.gif o.setState("ON");
43http://www.agoit.com/Images/OutliningIndicators/InBlock.gif c.saveMemento(o.createMemento());
44http://www.agoit.com/Images/OutliningIndicators/InBlock.gif o.setState("OFF");
45http://www.agoit.com/Images/OutliningIndicators/InBlock.gif o.restoreMemento(c.retrieveMemento());
46http://www.agoit.com/Images/OutliningIndicators/ExpandedSubBlockEnd.gif }
47http://www.agoit.com/Images/OutliningIndicators/ExpandedBlockEnd.gif}
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