°Ë±¦Êé¿â > ÎÄѧÆäËûµç×ÓÊé > VB2008´ÓÈëÃŵ½¾«Í¨(PDF¸ñʽӢÎÄ°æ) >

µÚ53²¿·Ö

VB2008´ÓÈëÃŵ½¾«Í¨(PDF¸ñʽӢÎÄ°æ)-µÚ53²¿·Ö

С˵£º VB2008´ÓÈëÃŵ½¾«Í¨(PDF¸ñʽӢÎÄ°æ) ×ÖÊý£º ÿҳ4000×Ö

°´¼üÅÌÉÏ·½Ïò¼ü ¡û »ò ¡ú ¿É¿ìËÙÉÏÏ·­Ò³£¬°´¼üÅÌÉ쵀 Enter ¼ü¿É»Øµ½±¾ÊéĿ¼ҳ£¬°´¼üÅÌÉÏ·½Ïò¼ü ¡ü ¿É»Øµ½±¾Ò³¶¥²¿£¡
¡ª¡ª¡ª¡ªÎ´ÔĶÁÍꣿ¼ÓÈëÊéÇ©ÒѱãÏ´μÌÐøÔĶÁ£¡




existed£»¡¡TaxEngine¡£CalculateTaxToPay£¨£©¡¡would¡¡have¡¡needed¡¡to¡¡call¡¡the¡¡base¡¡class¡¡functionality¡¡¡¡

to¡¡get¡¡the¡¡basic¡¡tax¡¡rate£»¡¡and¡¡then¡¡recalculate¡¡the¡¡taxable¡¡monies¡¡to¡¡figure¡¡out¡¡if¡¡the¡¡surtax¡¡applied¡£¡¡



¡öNote¡¡¡¡When¡¡you¡¡use¡¡Overrides¡¡with¡¡methods£»¡¡you¡¡are¡¡saying¡¡that¡¡you¡¡need¡¡something¡¡special¡£¡¡This¡¡does¡¡¡¡

not¡¡imply¡¡that¡¡the¡¡base¡¡class¡¡functionality¡¡will¡¡be¡¡called¡£¡¡It¡¡implies¡¡that¡¡you¡¡might¡¡call¡¡the¡¡base¡¡class¡¡functionality¡¡¡¡

and¡¡perform¡¡some¡¡additional¡¡operations¡£¡¡Thus£»¡¡when¡¡designing¡¡base¡¡class¡¡functionality£»¡¡it¡¡is¡¡important¡¡to¡¡¡¡

track¡¡calculations¡¡or¡¡operations¡¡using¡¡protected¡¡data¡¡members¡£¡¡The¡¡data¡¡members¡¡avoid¡¡having¡¡derived¡¡classes¡¡¡¡

perform¡¡the¡¡same¡¡operations¡¡multiple¡¡times£»¡¡slowing¡¡down¡¡the¡¡application¡¡and¡¡avoiding¡¡potential¡¡errors¡£¡¡



¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡USING¡¡NAMESPACES¡¡



¡¡¡¡¡¡Namespaces¡¡are¡¡used¡¡to¡¡define¡¡classes£»¡¡interfaces£»¡¡and¡¡structures¡¡that¡¡belong¡¡together¡£¡¡In¡¡this¡¡chapter¡¯s¡¡¡¡

¡¡¡¡¡¡example£»¡¡there¡¡is¡¡an¡¡American¡¡tax¡¡engine£»¡¡a¡¡Swiss¡¡tax¡¡engine£»¡¡and¡¡so¡¡on¡£¡¡For¡¡organizational¡¡purposes£»¡¡each¡¡¡¡

¡¡¡¡¡¡should¡¡have¡¡its¡¡own¡¡namespace¡£¡¡Sometimes¡¡you¡¡might¡¡even¡¡create¡¡a¡¡custom¡¡assembly¡¡for¡¡each¡¡set¡¡of¡¡inter

¡¡¡¡¡¡face¡¡implementations£»¡¡but¡¡you¡¡would¡¡still¡¡need¡¡to¡¡create¡¡a¡¡namespace¡£¡¡Creating¡¡a¡¡namespace¡¡is¡¡independent¡¡¡¡

¡¡¡¡¡¡of¡¡the¡¡fact¡¡of¡¡whether¡¡or¡¡not¡¡you¡¡create¡¡a¡¡separate¡¡assembly¡£¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡In¡¡the¡¡examples£»¡¡I¡¡use¡¡namespaces¡¡like¡¡Surtax¡¡and¡¡Canada¡£¡¡Whenever¡¡you¡¡create¡¡a¡¡class¡¡or¡¡a¡¡module£»¡¡¡¡

¡¡¡¡¡¡or¡¡some¡¡other¡¡type£»¡¡you¡¡can¡¡embed¡¡the¡¡type¡¡within¡¡the¡¡namespace¡£¡¡Then¡¡to¡¡use¡¡the¡¡newly¡¡defined¡¡¡¡

¡¡¡¡¡¡namespaces¡¡in¡¡code¡¡pieces¡¡that¡¡are¡¡not¡¡part¡¡of¡¡the¡¡namespace£»¡¡use¡¡the¡¡Imports¡¡keyword¡£¡¡¡¡



Abstracting¡¡Instantiations¡¡with¡¡Factories¡¡



Take¡¡a¡¡good¡¡look¡¡at¡¡the¡¡scope¡¡declaration¡¡of¡¡the¡¡tax¡¡engine¡¡shown¡¡earlier¡¡and¡¡pare¡¡it¡¡with¡¡¡¡

the¡¡scope¡¡declaration¡¡for¡¡the¡¡ITaxEngine¡¡interface¡£¡¡What¡¡you¡¡will¡¡notice¡¡is¡¡that¡¡¡¡ITaxEngine¡¡is¡¡¡¡

declared¡¡as¡¡Public¡¡scope£»¡¡as¡¡is¡¡BaseTaxEngine£»¡¡and¡¡TaxEngine¡¡is¡¡declared¡¡as¡¡¡¡Friend¡£¡¡Going¡¡back¡¡¡¡

to¡¡our¡¡project¡¡structure£»¡¡this¡¡scope¡¡declaration¡¡implies¡¡that¡¡any¡¡reference¡¡to¡¡LibTax¡¡will¡¡see¡¡the¡¡¡¡

interface¡¡ITaxEngine¡¡and¡¡¡¡BaseTaxEngine£»¡¡but¡¡not¡¡TaxEngine¡£¡¡For¡¡example£»¡¡the¡¡following¡¡test¡¡¡¡

code¡¡will¡¡not¡¡work¡£¡¡



Dim¡¡taxengine¡¡As¡¡ITaxEngine¡¡=¡¡New¡¡Surtax¡£TaxEngine£¨£©¡¡



¡¡¡¡¡¡¡¡¡¡¡¡The¡¡reason¡¡the¡¡test¡¡code¡¡will¡¡not¡¡work¡¡is¡¡that¡¡any¡¡type¡¡that¡¡is¡¡not¡¡declared¡¡with¡¡Public¡¡scope¡¡¡¡

is¡¡private¡¡to¡¡the¡¡solution¡¡containing¡¡the¡¡declaration¡£¡¡You¡¡may¡¡be¡¡thinking£»¡¡¡°That¡¯s¡¡great¡ªyou¡¡¡¡

declare¡¡a¡¡type¡¡that¡¡you¡¡cannot¡¡instantiate¡£¡¡So£»¡¡how¡¡can¡¡I¡¡use¡¡that¡¡type£¿¡±¡¡

¡¡¡¡¡¡¡¡¡¡¡¡The¡¡scope¡¡declarations¡¡are¡¡not¡¡a¡¡mistake¡¡and¡¡illustrate¡¡a¡¡design¡¡pattern¡¡called¡¡a¡¡factory¡¡¡£¡¡A¡¡¡¡

factory¡¡is¡¡a¡¡way¡¡of¡¡abstracting¡¡the¡¡instantiation¡¡away¡¡from¡¡the¡¡caller¡¡so¡¡that¡¡the¡¡interface¡¡can¡¡¡¡

vary¡¡from¡¡its¡¡implementation¡£¡¡In¡¡our¡¡restaurant¡¡analogy£»¡¡it¡¡means¡¡when¡¡you¡¡want¡¡a¡¡waiter£»¡¡you¡¡¡¡


¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­Page¡¡200¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­

178¡¡¡¡¡¡¡¡¡¡¡¡¡¡CH¡¡AP¡¡T¡¡E¡¡R¡¡¡¡¡¡7¡¡¡¡¡¡¡ö¡¡¡¡¡¡¡¡L¡¡E¡¡A¡¡R¡¡N¡¡IN¡¡G¡¡¡¡¡¡AB¡¡OU¡¡T¡¡¡¡¡¡CO¡¡M¡¡P¡¡O¡¡N¡¡E¡¡N¡¡TS¡¡¡¡¡¡AN¡¡D¡¡¡¡C¡¡L¡¡AS¡¡S¡¡¡¡H¡¡I¡¡E¡¡R¡¡AR¡¡C¡¡H¡¡IE¡¡S¡¡



¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡don¡¯t¡¡want¡¡to¡¡need¡¡to¡¡know¡¡his¡¡name¡£¡¡You¡¡would¡¡rather¡¡have¡¡a¡¡generic¡¡mechanism¡¡where¡¡the¡¡¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡restaurant¡¡presents¡¡to¡¡you¡¡the¡¡waiter¡£¡¡Otherwise£»¡¡to¡¡eat¡¡at¡¡a¡¡restaurant£»¡¡you¡¡would¡¡need¡¡to¡¡¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡know¡¡the¡¡name¡¡of¡¡your¡¡waiter¡¡before¡¡being¡¡able¡¡to¡¡order¡¡something¡£¡¡That¡¡would¡¡be¡¡inefficient¡£¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡The¡¡correct¡¡way¡¡of¡¡defining¡¡a¡¡factory¡¡is¡¡as¡¡follows£º¡¡



¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡Public¡¡Module¡¡EngineCreator¡¡¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡Public¡¡Function¡¡CreateSurtaxTaxEngine£¨£©¡¡As¡¡ITaxEngine¡¡¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡Return¡¡New¡¡Surtax¡£TaxEngine£¨£©¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡End¡¡Function¡¡



¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡'¡¡Required¡¡for¡¡country¡­specific¡¡tax¡¡calculations¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡Public¡¡Function¡¡CreateCanadianTaxEngine£¨£©¡¡As¡¡ITaxEngine¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡Return¡¡New¡¡Canada¡£TaxEngine£¨£©¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡End¡¡Function¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡End¡¡Module¡¡



¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡The¡¡factory¡¡is¡¡typically¡¡declared¡¡in¡¡a¡¡module¡¡because¡¡a¡¡module¡¡is¡¡not¡¡instantiated¡£¡¡Generally¡¡¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡speaking£»¡¡you¡¡don¡¯t¡¡want¡¡to¡¡add¡¡a¡¡factory¡¡to¡¡an¡¡object¡¡that¡¡can¡¡be¡¡instantiated¡¡because¡¡it¡¡could¡¡¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡result¡¡in¡¡context¡­specific¡¡instantiation¡£¡¡In¡¡other¡¡words£»¡¡you¡¡usually¡¡want¡¡a¡¡fresh¡¡object¡¡created¡¡¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡from¡¡scratch¡¡each¡¡time£»¡¡so¡¡it¡¯s¡¡not¡¡affected¡¡by¡¡the¡¡current¡¡state¡¡of¡¡the¡¡application¡£¡¡In¡¡the¡¡imple

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡mentation¡¡of¡¡CreateSurtaxTaxEngine£¨£©£»¡¡the¡¡type¡¡Surtax¡£TaxEngine¡¡is¡¡instantiated£»¡¡and¡¡the¡¡¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡instance¡¡is¡¡cast¡¡to¡¡the¡¡interface¡¡type¡¡ITaxEngine¡£¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡The¡¡EngineCreator¡¡module¡¡is¡¡declared¡¡with¡¡public¡¡scope£»¡¡implying¡¡any¡¡code¡¡that¡¡references¡¡¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡the¡¡assembly¡¡can¡¡see¡¡the¡¡module¡£¡¡Thus£»¡¡the¡¡test¡¡code¡¡can¡¡be¡¡rewritten¡¡as¡¡follows¡¡£¨we¡¡need¡¡to¡¡¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡import¡¡the¡¡LibTax¡¡project£»¡¡of¡¡course£©£º¡¡



¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡Dim¡¡taxengine¡¡As¡¡ITaxEngine¡¡=¡¡EngineCreator¡£CreateSurtaxTaxEngine£¨£©¡¡



¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡After¡¡calling¡¡¡¡EngineCreator¡£CreateSurtaxTaxEngine£¨£©£»¡¡the¡¡test¡¡code¡¡has¡¡a¡¡valid¡¡instance¡¡of¡¡¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡ITaxEngine¡£¡¡It¡¯s¡¡very¡¡important¡¡to¡¡note¡¡that¡¡the¡¡test¡¡code¡¡has¡¡no¡¡idea¡¡what¡¡type¡¡implemented¡¡¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡the¡¡interface¡£¡¡This¡¡allows¡¡the¡¡assembly¡¡to¡¡change¡¡which¡¡type¡¡is¡¡referenced¡¡in¡¡the¡¡implementa

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡tion¡¡of¡¡CreateSurtaxTaxEngine£¨£©¡¡without¡¡having¡¡to¡¡inform¡¡the¡¡caller¡¡of¡¡the¡¡method¡£¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡Putting¡¡this¡¡into¡¡the¡¡context¡¡of¡¡the¡¡restaurant£»¡¡it¡¡means¡¡waiters¡¡can¡¡be¡¡replaced¡£¡¡So¡¡if¡¡you¡¡¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡repeatedly¡¡visit¡¡a¡¡restaurant¡¡and¡¡get¡¡a¡¡waiter¡¡called¡¡John£»¡¡but¡¡one¡¡day¡¡John¡¡gets¡¡sick¡¡and¡¡is¡¡not¡¡¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡working£»¡¡you¡¡can¡¡still¡¡order¡¡and¡¡receive¡¡your¡¡food¡¡from¡¡the¡¡waitress¡¡called¡¡Mary¡£¡¡It¡¡would¡¡be¡¡a¡¡¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡bad¡¡idea¡¡for¡¡a¡¡restaurant¡¡to¡¡depend¡¡on¡¡a¡¡particular¡¡server¡¡for¡¡a¡¡particular¡¡guest¡£¡¡



¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡Using¡¡Default¡¡Implementations¡¡



¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡In¡¡some¡¡cases£»¡¡base¡¡classes¡¡are¡¡not¡¡necessary¡£¡¡Sometimes¡¡you¡¡can¡¡create¡¡a¡¡default¡¡implemen

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡tation¡¡that¡¡could¡¡span¡¡multiple¡¡subsystems¡£¡¡In¡¡the¡¡case¡¡of¡¡the¡¡tax¡¡engine£»¡¡an¡¡ine¡¡is¡¡an¡¡ine¡¡¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡in¡¡Canada£»¡¡an¡¡ine¡¡in¡¡the¡¡United¡¡States£»¡¡and¡¡an¡¡ine¡¡in¡¡Germany¡£¡¡What¡¡varies¡¡is¡¡how¡¡the¡¡¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡ine¡¡is¡¡treated¡¡in¡¡each¡¡country¡¡when¡¡calculating¡¡taxes¡£¡¡Another¡¡consistency¡¡across¡¡countries¡¡is¡¡¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡that¡¡if¡¡ine¡¡is¡¡a¡¡capital¡¡gain£»¡¡not¡¡all¡¡of¡¡the¡¡ine¡¡is¡¡taxable¡£¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡In¡¡the¡¡case¡¡of¡¡ine£»¡¡you¡¡can¡¡create¡¡an¡¡implementation¡¡that¡¡would¡¡be¡¡identical¡¡across¡¡¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡different¡¡tax¡¡engines£»¡¡as¡¡follows£º¡¡


¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­Page¡¡201¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡CH¡¡AP¡¡T¡¡E¡¡R¡¡¡¡¡¡7¡¡¡¡¡¡¡ö¡¡¡¡¡¡¡¡L¡¡E¡¡AR¡¡N¡¡IN¡¡G¡¡¡¡¡¡AB¡¡O¡¡U¡¡T¡¡¡¡¡¡CO¡¡M¡¡P¡¡O¡¡N¡¡E¡¡N¡¡TS¡¡¡¡¡¡AN¡¡D¡¡¡¡¡¡C¡¡L¡¡AS¡¡S¡¡¡¡H¡¡I¡¡E¡¡R¡¡AR¡¡C¡¡HI¡¡E¡¡S¡¡179¡¡



NotInheritable¡¡Class¡¡TaxIne¡¡¡¡

¡¡¡¡¡¡¡¡Implements¡¡ITaxIne¡¡



¡¡¡¡¡¡¡¡Private¡¡_amount¡¡As¡¡Double¡¡

¡¡¡¡¡¡¡¡Private¡¡_taxableRate¡¡As¡¡Double¡¡



¡¡¡¡¡¡¡¡Public¡¡Sub¡¡New£¨ByVal¡¡amount¡¡As¡¡Double£»¡¡ByVal¡¡taxableRate¡¡As¡¡Double£©¡¡¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡_amount¡¡=¡¡amount¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡_taxableRate¡¡=¡¡taxableRate¡¡

¡¡¡¡¡¡¡¡End¡¡Sub¡¡

¡¡¡¡¡¡¡¡¡¡

¡¡¡¡¡¡¡¡Public¡¡ReadOnly¡¡Property¡¡RealAmount£¨£©¡¡As¡¡Double¡¡_¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡Implements¡¡ITaxIne¡£RealAmount¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡Get¡¡¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡Return¡¡_amount¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡End¡¡Get¡¡

¡¡¡¡¡¡¡¡End¡¡Property¡¡



¡¡¡¡¡¡¡¡Public¡¡ReadOnly¡¡Property¡¡TaxableAmount£¨£©¡¡As¡¡Double¡¡_¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡Implements¡¡ITaxIne¡£TaxableAmount¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡Get¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡Return¡¡_amount¡¡*¡¡_taxableRate¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡End¡¡Get¡¡

¡¡¡¡¡¡¡¡End¡¡Property¡¡

End¡¡Class¡¡



¡¡¡¡¡¡¡¡¡¡The¡¡ITaxIne¡¡interface¡¡has¡¡two¡¡properties¡¡that¡¡are¡¡implemented¡¡in¡¡TaxIne£º¡¡RealAmount¡¡¡¡

and¡¡TaxableAmount¡£¡¡The¡¡values¡¡for¡¡the¡¡two¡¡properties¡¡are¡¡considered¡¡read¡­only¡¡and¡¡are¡¡defined¡¡¡¡

by¡¡the¡¡constructor¡¡of¡¡TaxIne¡£¡¡The¡¡purpose¡¡of¡¡the¡¡constructor¡¡is¡¡to¡¡assign¡¡two¡¡values¡¡and¡¡¡¡

then¡¡consider¡¡the¡¡object¡¡as¡¡immutable¡£¡¡If¡¡you¡¡wanted¡¡to¡¡change¡¡the¡¡values¡¡of¡¡the¡¡ITaxIne¡¡¡¡

interface£»¡¡you¡¡would¡¡need¡¡to¡¡instantiate¡¡a¡¡new¡¡instance¡¡of¡¡TaxIne¡£¡¡While¡¡it¡¡sounds¡¡like¡¡a¡¡pain¡¡¡¡

to¡¡need¡¡to¡¡instantiate¡¡a¡¡new¡¡instance¡¡whenever¡¡you¡¡want¡¡to¡¡change¡¡the¡¡value¡¡of¡¡the¡¡RealAmount¡¡and¡¡¡¡

TaxableAmount¡¡properties£»¡¡this¡¡approach¡¡has¡¡some¡¡advantages¡¡in¡¡terms¡¡of¡¡performance¡¡and¡¡¡¡

resource¡¡management¡£¡¡

¡¡¡¡¡¡¡¡¡¡In¡¡the¡¡sample¡¡code£»¡¡the¡¡TaxableAmount¡¡property¡¡is¡¡the¡¡result¡¡of¡¡multiplying¡¡the¡¡data¡¡members¡¡¡¡

_amount¡¡and¡¡_taxableRate¡£¡¡For¡¡example£»¡¡when¡¡calculating¡¡the¡¡taxable¡¡ine¡¡of¡¡a¡¡capital¡¡gain¡¡¡¡

in¡¡Canada£»¡¡you¡¡multiply¡¡the¡¡total¡¡amount¡¡by¡¡50£¥¡£¡¡Thus£»¡¡the¡¡_taxableRate¡¡data¡¡member¡¡would¡¡¡¡

have¡¡a¡¡value¡¡of¡¡0¡£50¡£¡¡

¡¡¡¡¡¡¡¡¡¡Another¡¡item¡¡to¡¡note¡¡is¡¡that¡¡the¡¡declaration¡¡of¡¡TaxIne¡¡is¡¡lacking¡¡a¡¡Public¡¡scope£»¡¡but¡¡has¡¡¡¡

a¡¡NotInheritable¡¡keyword¡¡prefixed¡¡to¡¡the¡¡identifier¡£¡¡When¡¡a¡¡class¡¡is¡¡prefixed¡¡with¡¡NotInheritable£»¡¡¡¡

it¡¡means¡¡that¡¡the¡¡class¡¡cannot¡¡be¡¡subclassed¡£¡¡From¡¡a¡¡design¡¡perspective£»¡¡the¡¡code¡¡is¡¡saying¡¡¡¡

TaxIne¡¡is¡¡a¡¡shared¡¡class¡¡that¡¡should¡¡not¡¡be¡¡subclassed¡¡lest¡¡it¡¡affect¡¡the¡¡shared¡¡behavior¡£¡¡¡¡

¡¡¡¡¡¡¡¡¡¡The¡¡NotInheritable¡¡keyword¡¡can¡¡also¡¡be¡¡applied¡¡to¡¡a¡¡method£»¡¡which¡¡means¡¡that¡¡the¡¡method¡¡¡¡

cannot¡¡be¡¡overloaded¡¡or¡¡overridden¡£¡¡You¡¡would¡¡use¡¡NotOverridable¡¡on¡¡a¡¡method¡¡when¡¡you¡¡do¡¡¡¡

not¡¡want¡¡a¡¡derived¡¡class¡¡to¡¡change¡¡the¡¡behavior¡¡of¡¡the¡¡method¡£¡¡Though¡¡to¡¡be¡¡able¡¡to¡¡use¡¡the¡¡¡¡

NotOverridable¡¡keyword£»¡¡you¡¡first¡¡need¡¡to¡¡define¡¡a¡¡method¡¡that¡¡overrides¡¡another¡¡method¡£¡¡


¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­Page¡¡202¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­

180¡¡¡¡¡¡¡¡¡¡¡¡¡¡CH¡¡AP¡¡T¡¡E¡¡R¡¡¡¡¡¡7¡¡¡¡¡¡¡ö¡¡¡¡¡¡¡¡L¡¡E¡¡A¡¡R¡¡N¡¡IN¡¡G¡¡¡¡¡¡AB¡¡OU¡¡T¡¡¡¡¡¡CO¡¡M¡¡P¡¡O¡¡N¡¡E¡¡N¡¡TS¡¡¡¡¡¡AN¡¡D¡¡¡¡C¡¡L¡¡AS¡¡S¡¡¡¡H¡¡I¡¡E¡¡R¡¡AR¡¡C¡¡H¡¡IE¡¡S¡¡



¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡The¡¡implementation¡¡of¡¡¡¡ITaxDeduction¡¡is¡¡similar¡¡to¡¡¡¡ITaxIne£º¡¡



¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡NotInheritable¡¡Class¡¡TaxDeduction¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡Implements¡¡ITaxDeduction¡¡



¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡Private¡¡_amount¡¡As¡¡Double¡¡



¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡Public¡¡Sub¡¡New£¨ByVal¡¡amount¡¡As¡¡Double£©¡¡¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡_amount¡¡=¡¡amount¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡End¡¡Sub¡¡



¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡Public¡¡ReadOnly¡¡Property¡¡Amount£¨£©¡¡As¡¡Double¡¡_¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡Implements¡¡ITaxDeduction¡£Amount¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡Get¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡Return¡¡_amount¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡End¡¡Get¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡End¡¡Property¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡End¡¡Class¡¡



¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡TaxIne¡¡and¡¡TaxDeduction¡¡are¡¡sealed¡¡classes¡¡because¡¡the¡¡functionality¡¡will¡¡be¡¡shared¡¡¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡among¡¡implementations¡£¡¡But¡¡is¡¡it¡¡wise¡¡to¡¡expose¡¡the¡¡interfaces¡¡and¡¡not¡¡the¡¡classes¡¡themselves£¿¡¡¡¡

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡

·µ»ØĿ¼ ÉÏÒ»Ò³ ÏÂÒ»Ò³ »Øµ½¶¥²¿ ÔÞ£¨0£© ²È£¨1£©

Äã¿ÉÄÜϲ»¶µÄ