计算机专业毕业设计中英对照外文翻译-对象的创建和存在时间

计算机专业毕业设计中英对照外文翻译-对象的创建和存在时间

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1、外文资料ObjectlandscapesandlifetimesTechnically,OOPisjustaboutabstractdatatyping,inheritance,andpolymorphism,butotherissuescanbeatleastasimportant.Theremainderofthissectionwillcovertheseissues.Oneofthemostimportantfactorsisthewayobjectsarecreatedanddestroyed.Whereisthedataforano

2、bjectandhowisthelifetimeoftheobjectcontrolled?Therearedifferentphilosophiesatworkhere.C++takestheapproachthatcontrolofefficiencyisthemostimportantissue,soitgivestheprogrammerachoice.Formaximumrun-timespeed,thestorageandlifetimecanbedeterminedwhiletheprogramisbeingwritten,byp

3、lacingtheobjectsonthestack(thesearesometimescalledautomaticorscopedvariables)orinthestaticstoragearea.Thisplacesapriorityonthespeedofstorageallocationandrelease,andcontrolofthesecanbeveryvaluableinsomesituations.However,yousacrificeflexibilitybecauseyoumustknowtheexactquanti

4、ty,lifetime,andtypeofobjectswhileyou'rewritingtheprogram.Ifyouaretryingtosolveamoregeneralproblemsuchascomputer-aideddesign,warehousemanagement,orair-trafficcontrol,thisistoorestrictive.Thesecondapproachistocreateobjectsdynamicallyinapoolofmemorycalledtheheap.Inthisapproach,

5、youdon'tknowuntilrun-timehowmanyobjectsyouneed,whattheirlifetimeis,orwhattheirexacttypeis.Thosearedeterminedatthespurofthemomentwhiletheprogramisrunning.Ifyouneedanewobject,yousimplymakeitontheheapatthepointthatyouneedit.Becausethestorageismanageddynamically,atrun-time,theam

6、ountoftimerequiredtoallocatestorageontheheapissignificantlylongerthanthetimetocreatestorageonthestack.(Creatingstorageonthestackisoftenasingleassemblyinstructiontomovethestackpointerdown,andanothertomoveitbackup.)Thedynamicapproachmakesthegenerallylogicalassumptionthatobject

7、stendtobecomplicated,sotheextraoverheadoffindingstorageandreleasingthatstoragewillnothaveanimportantimpactonthecreationofanobject.Inaddition,thegreaterflexibilityisessentialtosolvethegeneralprogrammingproblem.Javausesthesecondapproach,exclusively].Everytimeyouwanttocreateano

8、bject,youusethenewkeywordtobuildadynamicinstanceofthatobject.There'sanother

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