Effective Java 2nd Edition【外文翻译】

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1、外文翻译原文EffectiveJava2ndEditionMaterialSource:AddisonWesleyAuthor:JoshuaBlochAvoidcreatingunnecessaryobjects:Itisoftenappropriatetoreuseasingleobjectinsteadofcreatinganewfunctionallyequivalentobjecteachtimeitisneeded.Reusecanbebothfasterandmorestylish.Anobjectc

2、analwaysbereusedifitisimmutable.Asanextremeexampleofwhatnottodo,considerthisstatement:Strings=newString("stringette");//DON'TDOTHIS!ThestatementcreatesanewStringinstanceeachtimeitisexecuted,andnoneofthoseobjectcreationsisnecessary.TheargumenttotheStringconstr

3、uctor("stringette")isitselfaStringinstance,functionallyidenticaltoalloftheobjectscreatedbytheconstructor.Ifthisusageoccursinalooporinafrequentlyinvokedmethod,millionsofStringinstancescanbecreatedneedlessly.Theimprovedversionissimplythefollowing:Strings="strin

4、gette";ThisversionusesasingleStringinstance,ratherthancreatinganewoneeachtimeitisexecuted.Furthermore,itisguaranteedthattheobjectwillbereusedbyanyothercoderunninginthesamevirtualmachinethathappenstocontainthesamestringliteral[JLS,3.10.5].Youcanoftenavoidcreat

5、ingunnecessaryobjectsbyusingstaticfactorymethodsinpreferencetoconstructorsonimmutableclassesthatprovideboth.Forexample,thestaticfactorymethodBoolean.valueOf(String)isalmostalwayspreferabletotheconstructorBoolean(String).Theconstructorcreatesanewobjecteachtime

6、it'scalled,whilethestaticfactorymethodisneverrequiredtodosoandwon'tinpractice.Eliminateobsoleteobjectreferences:Generallyspeaking,wheneveraclassmanagesitsownmemory,theprogrammershouldbealertformemoryleaks.Wheneveranelementisfreed,anyobjectreferencescontainedi

7、ntheelementshouldbenulledout.Anothercommonsourceofmemoryleaksiscaches.Onceyouputanobjectreferenceintoacache,it'seasytoforgetthatit'sthereandleaveitinthecachelongafteritbecomesirrelevant.Thereareseveralsolutionstothisproblem.Ifyou'reluckyenoughtoimplementacach

8、eforwhichanentryisrelevantexactlysolongastherearereferencestoitskeyoutsideofthecache,representthecacheasaWeakHashMap;entrieswillberemovedautomaticallyaftertheybecomeobsolete.RememberthatW