1: 寬接口和白箱：
2: 發(fā)起人角色
3: public class Originator{ 4: private String state;
5:
6: //工廠方法，返還一個(gè)新的備忘錄對(duì)象
7: public Memento createMemento(){ 8: return new Memento(state);
9: }
10:
11: //將發(fā)起人恢復(fù)到備忘錄對(duì)象所記載的狀態(tài)
12: public void restoreMemento(Memento memento){ 13: this.state = memento.getState();
14: }
15:
16: //狀態(tài)的取值方法
17: public String getState(){ 18: return this.state;
19: }
20:
21: //狀態(tài)的賦值方法
22: public void setState(String state){ 23: this.state = state;
24: System.out.println("Current state = " + this.state); 25: }
26: }
27:
28: 備忘錄模式要求備忘錄對(duì)象提供兩個(gè)不同的接口：一個(gè)寬接口提供給發(fā)起人對(duì)象，另一個(gè)窄接口提供給所有其他的對(duì)象，包括負(fù)責(zé)人對(duì)象。
29: 寬接口允許發(fā)起人讀取到所有的數(shù)據(jù)；窄接口只允許它把備忘錄對(duì)象傳給其他的對(duì)象而看不到內(nèi)部的數(shù)據(jù)。
30: //備忘錄角色
31: public class Memento{ 32: private String state;
33:
34: public Memento(String state){ 35: this.state = state;
36: }
37:
38: public String getState(){ 39: return this.state;
40: }
41:
42: public void setState(String state){ 43: this.state = state;
44: }
45: }
46:
47: 負(fù)責(zé)人角色負(fù)責(zé)保存?zhèn)渫泴?duì)象，但是從不修改（甚至不查看）備忘錄對(duì)象的內(nèi)容（一個(gè)更好的實(shí)現(xiàn)是負(fù)責(zé)人對(duì)象根本無法從備忘錄
48: 對(duì)象中讀取個(gè)修改其內(nèi)容）
49:
50: //負(fù)責(zé)人角色
51: public class Caretaker{ 52: private Memento memento;
53:
54: //備忘錄的取值方法
55: public Memento retrieveMemento(){ 56: return this.memento;
57: }
58:
59: //備忘錄的賦值方法
60: public void saveMemento(Memento memento){ 61: this.memento = memento;
62: }
63: }
64:
65: //客戶端
66: public class Client{ 67: private static Originator o = new Originator();
68: private static Caretaker c= new Caretaker();
69: private static void main(String[] args){ 70: //該負(fù)責(zé)人對(duì)象的狀態(tài)
71: o.setState("On"); 72: //創(chuàng)建備忘錄對(duì)象，并將發(fā)起人對(duì)象的狀態(tài)存儲(chǔ)起來
73: c.saveMemento(o.createMemento());
74: //修改發(fā)起人對(duì)象的狀態(tài)
75: o.setState("Off"); 76: //恢復(fù)發(fā)起人對(duì)象的狀態(tài)
77: o.restoreMemento(c.retrieveMemento());
78: }
79: }
80: 首先將發(fā)起人對(duì)象的狀態(tài)設(shè)置成“On”（或者任何有效狀態(tài)），并且創(chuàng)建一個(gè)備忘錄對(duì)象將這個(gè)狀態(tài)存儲(chǔ)起來；然后將發(fā)起人對(duì)象
81: 的狀態(tài)改成“Off”（或者任何狀態(tài)）；最后又將發(fā)起人對(duì)象恢復(fù)到備忘錄對(duì)象所存儲(chǔ)起來的狀態(tài)，即“On”狀態(tài)（或者先前所
82: 存儲(chǔ)的任何狀態(tài)）
83:
84: 備忘錄系統(tǒng)運(yùn)行的時(shí)序是這樣的：
85: （1）將發(fā)起人對(duì)象的狀態(tài)設(shè)置成“On”。
86: （2）調(diào)用發(fā)起人角色的createMemento()方法，創(chuàng)建一個(gè)備忘錄對(duì)象將這個(gè)狀態(tài)存儲(chǔ)起來。
87: （3）將備忘錄對(duì)象存儲(chǔ)到負(fù)責(zé)人對(duì)象中去。
88: 備忘錄系統(tǒng)恢復(fù)的時(shí)序是這樣的：
89: （1）將發(fā)起人對(duì)象的狀態(tài)設(shè)置成“Off”；
90: （2）將備忘錄對(duì)象從負(fù)責(zé)人對(duì)象中取出；
91: （3）將發(fā)起人對(duì)象恢復(fù)到備忘錄對(duì)象所存儲(chǔ)起來的狀態(tài)，“On”狀態(tài)。
92:
93: 白箱實(shí)現(xiàn)的優(yōu)缺點(diǎn)
94: 白箱實(shí)現(xiàn)的一個(gè)明顯的好處是比較簡(jiǎn)單，因此常常用做教學(xué)目的。白箱實(shí)現(xiàn)的一個(gè)明顯的缺點(diǎn)是破壞對(duì)發(fā)起人狀態(tài)的封裝。
95:
96: 窄接口或者黑箱實(shí)現(xiàn)
97: //發(fā)起人角色
98: public class Originator{ 99: private String state;
100:
101: public Originator(){ 102: }
103:
104: //工廠方法，返還一個(gè)新的備忘錄對(duì)象
105: public MementoIF createMemento(){ 106: return new Memento(this.state);
107: }
108:
109: //將發(fā)起人恢復(fù)到備忘錄對(duì)象記錄的狀態(tài)
110: public void restoreMemento(MementoIF memento){ 111: Memento aMemento = (Memento)memento;
112: this.setState(aMemento.getState());
113: }
114:
115: public String getState(){ 116: return this.state;
117: }
118:
119: public void setState(){ 120: this.state = state;
121: System.out.println("state = " + state); 122: }
123:
124: protected class Memento implements MementoIF{ 125: private String savedState;
126: private Mememto(String someState){ 127: savedState = someState;
128: }
129:
130: private void setState(String someState){ 131: savedState = someState;
132: }
133:
134: private String getState(){ 135: return savedState;
136: }
137: }
138: }
139:
140: public interface MementoIF{} 141:
142: public class Caretaker{ 143: private MementoIF memento;
144:
145: public MementoIF retrieveMemento(){ 146: return this.memento;
147: }
148:
149: public void saveMemento(MementoIF memento){ 150: this.memento = memento;
151: }
152: }
153:
154: public class Client{ 155: private static Originator o = new Originator();
156: private static Caretaker c = new Caretaker();
157:
158: public static void main(String args[]){ 159: //改變負(fù)責(zé)人對(duì)象的狀態(tài)
160: o.setState("On"); 161: //創(chuàng)建備忘錄對(duì)象，并將發(fā)起人對(duì)象的狀態(tài)存儲(chǔ)起來
162: c.saveMemento(o.createMemento());
163: //修改發(fā)起人對(duì)象的狀態(tài)
164: o.setState("Off"); 165: //恢復(fù)發(fā)起人對(duì)象的狀態(tài)
166: o.restoreMemento(c.retrieveMemento());
167: }
168: }
169:
170: 黑箱實(shí)現(xiàn)運(yùn)行時(shí)的時(shí)序?yàn)?
171: (1)將發(fā)起人對(duì)象的狀態(tài)設(shè)置成“On”。
172: （2）調(diào)用發(fā)起人角色的 createMemento()方法，創(chuàng)建一個(gè)備忘錄對(duì)象將這個(gè)狀態(tài)存儲(chǔ)起來。
173: （3）將備忘錄對(duì)象存儲(chǔ)到負(fù)責(zé)人對(duì)象中去。由于負(fù)責(zé)人對(duì)象拿到的僅是 MementoIF類型，因此無法讀出備忘錄內(nèi)部的狀態(tài)。
174: 恢復(fù)時(shí)的時(shí)序?yàn)椋?/pre> 175: （1）將發(fā)起人對(duì)象的狀態(tài)設(shè)置成“Off”；
176: （2）將備忘錄對(duì)象從負(fù)責(zé)人對(duì)象中取出。注意此時(shí)僅能得到 MementoIF接口，因此無法讀出此對(duì)象的內(nèi)部狀態(tài)
177: （3）將發(fā)起人對(duì)象的狀態(tài)恢復(fù)成備忘錄對(duì)象所存儲(chǔ)起來的狀態(tài)，，由于發(fā)起人對(duì)象的內(nèi)部類Memento實(shí)現(xiàn)了MementoIF接口
178: 這個(gè)內(nèi)部類是傳入的備忘錄對(duì)象的真實(shí)類型，因此發(fā)起人對(duì)象可以利用內(nèi)部類Memento 的私有 接口讀出此對(duì)象的內(nèi)部狀態(tài)
179:
180: 存儲(chǔ)多個(gè)狀態(tài)的備忘錄模式：
181: //發(fā)起人角色
182: import java.util.Vector;
183: import java.util.Enumeration;
184:
185: public class Originator{ 186: private Vector states;
187: private int index;
188:
189: public Originator(){ 190: states = new Vector();
191: index = 0;
192: }
193:
194: public Memento createMementor(){ 195: return new Mementor(states,index);
196: }
197:
198: public void restoreMementor(Mementor memento){ 199: states = memento.getStates();
200: index = memento.getIndex（）；
201: }
202:
203: public void setState(String state){ 204: this.states.addElement(state);
205: index ++;
206: }
207:
208: //輔助方法，打印出所有的狀態(tài)
209: public void printStates(){ 210: System.out.println("Total number of states: " + index); 211: for(Enumeration e = states.elements();e.hasMoreElements();){ 212: system.out.println(e.nextElement());
213: }
214: }
215: }
216:
217: //備忘錄角色
218: import java.util.Vector;
219:
220: public class Memento{ 221: private Vector states;
222: private int index;
223:
224: public Memento(Vector states,int index){ 225: this.states = (Vector)states.clone();
226: this.index = index;
227: }
228:
229: //狀態(tài)取值方法
230: Vector getStates(){ 231: return states;
232: }
233:
234: //檢查點(diǎn)取值方法
235: int getIndex(){ 236: return this.index;
237: }
238: }
239: ******************備忘錄的構(gòu)造子克隆了傳入的states，然后將克隆存入到備忘錄對(duì)象內(nèi)部，這是一個(gè)重要的細(xì)節(jié)，因?yàn)椴贿@樣的話，將會(huì)
240: 將會(huì)造成客戶端和備忘錄對(duì)象持有對(duì)同一個(gè)Vector對(duì)象的引用，也可以同時(shí)修改這個(gè)Vector對(duì)象，會(huì)造成系統(tǒng)崩潰。
241:
242: //負(fù)責(zé)人角色
243: import java.util.Vector;
244:
245: public class Caretaker{ 246: private Originator o;
247: private Vector mementos = new Vector();
248: private int current;
249:
250: public Caretaker(Originator o){ 251: this.o = o;
252: current = 0;
253: }
254:
255: public int createMemento(){ 256: Memento memento = o.createMemento();
257: mementos.addElement(memento);
258: return current ++;
259: }
260:
261: //將發(fā)起人恢復(fù)到某個(gè)檢查點(diǎn)
262: public void restoreMemento(int index){ 263: Memento memento = (Memento)mementos.elementAt(index);
264: o.restoreMemento(memento);
265: }
266:
267: //某個(gè)檢查點(diǎn)刪除
268: public void removeMemento(int index){ 269: mementos.removeElementAt(index);
270: }
271: }
272:
273: //客戶端
274: public class Client{ 275: private static Originator o = new Originator();
276: private static Caretaker c = new Caretaker(o);
277: public static void main(String[] args){ 278: //改變狀態(tài)
279: o.setState("state 0"); 280: //建立一個(gè)檢查點(diǎn)
281: c.createMemento();
282: //改變狀態(tài)
283: o.setState("state 1"); 284:
285: c.createMemento();
286:
287: o.setState("state 2"); 288:
289: c.createMemento();
290:
291: o.setState("state 3"); 292:
293: c.createMemento();
294:
295: o.setState("state 4"); 296:
297: c.createMemento();
298:
299: o.printStates();
300:
301: //恢復(fù)到第二個(gè)檢查點(diǎn)
302: System.out.println("Restoring to 2"); 303:
304: c.restoreMemento(2);
305:
306: o.printStates();
307:
308: System.out.println("Restoring to 0"); 309:
310: c.restoreMemento(0);
311:
312: o.printStates();
313:
314: System.out.println("Restoring to 3"); 315:
316: c.restoreMemento(3);
317:
318: o.printStates();
319:
320:
321: }
322: }
323:
324: 自述歷史模式（備忘錄模式的一個(gè)變種）：
325: //窄接口
326: public interface MementoIF{} 327:
328: //發(fā)起人角色
329: public class Originator{ 330: public String state;
331:
332: public Originator(){} 333:
334: public void changeState(String state){ 335: this.state = state;
336: System.out.println("State has been changed to : " + state); 337: }
338:
339: public Memento createMemento(){ 340: return new Memento(this);
341: }
342:
343: public void restoreMemento(MementoIF memento){ 344: Memento m = (Memento)memento;
345: changeState(m.state);
346: }
347:
348: class Memento implements MementoIF{ 349: private String state;
350:
351: private String getState(){ 352: return state;
353: }
354:
355: private Memento(Originator o){ 356: this.state = o.state;
357: }
358: }
359: }
360:
361: //客戶端
362: public class Client{ 363: private static Originator o;
364: private static MementoIF memento;
365:
366: public static void main(String args[]){ 367: o = new Originator();
368: o.changeState("State 1"); 369: memento = o.createMemento();
370: o.changeState("State 2"); 371: o.restoreMemento(memento);
372: }
373: }
374: