2021年SCJP認(rèn)證考試題庫(kù)

QUESTION61GIVENTHEEXHIBIT：Whichstatementistrue?A.Alloftheassertstatementsareusedappropriately.B.Onlytheassertstatementonline31isusedappropriatelyC.Theassertstatementsonlines29and31areusedappropriatelyD.Theassertstatementsonlines26and29areusedappropriatelyE.Theassertstatementsonlines29and33areusedappropriatelyF.Theassertstatementsonlines29,31and33areusedappropriatelyG.Theassertstatementsonlines26,29and31areusedappropriately斷言應(yīng)當(dāng)用在“你以為”你程序不也許產(chǎn)生錯(cuò)誤地方，并且有無(wú)啟用斷言，都不會(huì)影響程序正常運(yùn)營(yíng)。斷言使用限制：不要在public辦法中，用斷言來(lái)檢查參數(shù)對(duì)的性；不要讓斷言語(yǔ)句去解決某些程序必要流程。因素：1.public辦法會(huì)被別人調(diào)用，你不能保證她一定啟用斷言；如果沒(méi)有啟用，那么用斷言來(lái)做參數(shù)檢查也就沒(méi)故意義了。因此不要用斷言來(lái)檢查參數(shù)，公共辦法參數(shù)一定要用代碼執(zhí)行檢查； 2.如果用斷言來(lái)控制程序執(zhí)行流程，如果沒(méi)有啟用斷言，那么程序就不能對(duì)的執(zhí)行下去。此外，斷言語(yǔ)句不可以有任何邊界效應(yīng)，不要使用斷言語(yǔ)句去修變化量和變化辦法返回值，如果這樣當(dāng)啟動(dòng)斷言和不啟動(dòng)斷言執(zhí)行成果會(huì)截然不同。斷言使用時(shí)機(jī)：檢查流程不變性：在if-elseswitch-case預(yù)期成果之外可以加上斷言做額外檢查。內(nèi)部執(zhí)行不變性：if(true){return;}assertfalse;檢查私有辦法參數(shù)，成果等程序運(yùn)營(yíng)中一致性斷言語(yǔ)句不是永遠(yuǎn)會(huì)執(zhí)行，可以屏蔽也可以啟用

javac–source1.4*.java需要java–ea啟用assert；當(dāng)判斷條件為FALSE時(shí)就拋出錯(cuò)誤。Answer：(C)26行不適當(dāng)：不要對(duì)public辦法參數(shù)斷言29適當(dāng)：程序員在程序中最不大也許到達(dá)地方斷言

31適當(dāng)：斷言private辦法參數(shù)

33行不適當(dāng)：?jiǎn)⒂煤筒粏⒂脭嘌詴?huì)產(chǎn)生不同程序執(zhí)行序

參照大綱：異常解決—斷言和AssertionErrorQUESTION62GIVENTHEEXHIBIT：Whatistheresult?A. nullB. zeroC. someD. CompilationfailsE. AnexceptionisthrownatruntimeAnswer：(D)13行會(huì)報(bào)錯(cuò)，應(yīng)在15行使用elseif參照大綱：流程控制QUESTION63Giventheexhibit：Whatistheresult?A.testB.ExceptionC.CompilationfailsD.NullPointerExceptionAnswer：(C)18行出錯(cuò)，應(yīng)當(dāng)先catch子異常，再catchException；13行把a(bǔ)rgs賦null，14行會(huì)報(bào)NullPointerException如果沒(méi)有第13行運(yùn)營(yíng)時(shí)14行會(huì)報(bào)ArrayIndexOutOfBoundsException異常。參照大綱：異常解決QUESTION64Giventheexhibit：Whatistheresult?A.CompilationfailsB.aAaAaAaAAaaAaAC.AAaaAaAaAaaAaAD.AaAAAaaaAaAaAaE.aAaAaAaAaAAAaaF.AnexceptionisthrownatruntimeAnswer：(C)第10行將對(duì)strings這個(gè)集合做自然排序(ASCII小到大，一種一種比較)Collections.sort(Listlist)對(duì)list進(jìn)行排序，對(duì)set不能排序！List里可以放對(duì)象，因此當(dāng)list里面存儲(chǔ)是對(duì)象時(shí)候就不能用Collections.sort(Listlist)去排序了。由于JVM不懂得用什么規(guī)則去排序?。≈挥邪褜?duì)象類(lèi)實(shí)現(xiàn)Comparable接口，然后改寫(xiě)compareTo()參照大綱：集合QUESTION65Giventheexhibit：Whatistheresult?A.0B.1C.2D.3E.4F.Compilationfails.G.AnexceptionisthrownatruntimeAnswer：(D)Set中存儲(chǔ)元素是無(wú)序不重復(fù)。如果你想Set里Add一種元素，一方面她會(huì)去調(diào)用equals辦法，判斷set中與否有該元素，如果有則不更改set值并返回false，如果沒(méi)有，則把元素添加進(jìn)去，并返回true。Ws1ws2是自定義類(lèi)，ws1和ws2equals不相等；Stringequals辦法已經(jīng)改寫(xiě)，s1和s2相等；比較兩個(gè)對(duì)象與否相似,先比較hashcode，如果相似,在用equals辦法比較.如果都相似則兩個(gè)對(duì)象就以為是相似.Hashcode是把對(duì)象內(nèi)存地址通過(guò)運(yùn)算得來(lái).基本數(shù)據(jù)類(lèi)型和基本數(shù)據(jù)類(lèi)型包裝類(lèi)尚有String類(lèi)都已經(jīng)覆蓋了hashcode()，equals(),因此這些對(duì)象值只要同樣就以為對(duì)象同樣.參照大綱：集合QUESTION66Givenapre-genericsimplementationofamethod：Whichthreechangesmustbemadetothemethodsumtousegenerics?(choosethree)A.removeline14B.replaceline14with"inti=iter.next()；"C.replaceline13with"for(inti：intList){"D.replaceline13with"for(Iteratoriter：intList)"E.replacethemethoddeclarationwith"sum(List<int>intList)"F.replacethemethoddeclarationwith"sum(List<Integer>intList)"Answer：(A，C，F(xiàn))publicstaticintsum(List<Integer>intList){intsum=0;for(inti：intList){ sum+=i;}returnsum;}參照大綱：集合和泛型Whatistheresult?A.Compilationfailsduetoanerrorinline23.B.Compilationfailsduetoanerrorinline29.C.AClassCastExceptationoccursinline29.D.AClassCastExceptationoccursinline31.E.Thevalueofallfourobjectprintsinnaturalorder.Answer：(C)Arrays.sort(Object[]a)辦法中，a每一種元素都必要是互相可以比較（調(diào)用pareTo(Objecto2)）。否則會(huì)報(bào)ClassCastException異常。參照大綱：泛型QUESTION68PlacethecodeintopositiontocreateaclassthatmapsfromStringstoIntegervalues.Theresultofexecutionmustbe[one].Someoptionsmaybeusedmorethanonce.Answer：()publicclassNumberNames{ privateHashMap<String，Integer>map=newHashMap<String，Integer>(); publicvoidput(Stringname，Integervalue){ map.put(name，value); } publicSet<String>getNames(){ Returnmap.keySet(); }}QUESTION69Placearesultontoeachmethodcalltoindicatewhatwouldhappenifthemethodcallwereinsertedatline9.Note：Resultscanbeusedmorethanonce.Answer：()MethodResultm1(listA)Compilesandrunswithouterror泛型規(guī)范沒(méi)問(wèn)題m2(listA)Compilesandrunswithouterror泛型規(guī)范沒(méi)問(wèn)題m1(listB)CompilesandrunswithouterrorB是A子類(lèi)，泛型規(guī)范沒(méi)問(wèn)題m2(listB)Doesnotcompilem1(listO)Doesnotcompilem2(listO)DoesnotcompileQUESTION70Giventheexhibit:Whatistheresult?A.apple:appleB.carrot:appleC.apple:bananaD.banana:appleE.carrot:carrotF.carrot:bananaAnswer：(C)PriorityQueue優(yōu)先級(jí)隊(duì)列：預(yù)設(shè)是自然排序，因而pq內(nèi)元素順序?qū)⑹莂pple->banana->carrotpoll()取第一種元素，取完之后刪除，peek取第一種元素，并不刪除元素QUESTION71Given：AprogrammerisdevelopingaclassKey，thatwillbeusedasakeyinastandardjava.util.HashMap.Whichtwomethodsshouldbeoverriddentoassurethatkeyworkscorrectlyasakey?(choosetwo)A.publicinthashCode()B.publicBooleanequals(Keyk)C.publicintcompareTo(Objecto)D.publicBooleanequals(Objecto)Answer：(A，D)HashMap中key不能重復(fù)，因而必要實(shí)現(xiàn)hashCode和equals辦法QUESTION72---Giventheexhibit：Whichtwo，insertedatline2willallowthecodetocompile?(ChooseTwo)A.publicclassMinMax<?>{B.publicclassMinMax<?extendsNumber>{C.publicclassMinMax<NextendsObject>{D.publicclassMinMax<NextendsNumber>{E.publicclassMinMax<?extendsObject>{F.publicclassMinMax<NextendsInteger>{Answer：(D，F(xiàn))N是泛型類(lèi)別變量，它相稱于一種類(lèi)型。A 類(lèi)聲明是不能用？這個(gè)萬(wàn)用字符。B 同上C Object沒(méi)有doubleValue()辦法。D OK.E 同A。F OK.QUESTION73Giventheexhibit：enumExample{ONE，TWO，THREE}Whichstatementistrue?A.Theexpressions(ONE==ONE)andONE.equals(ONE)arebothguaranteedtobetrue.B.Theexpression(ONE<TWO)isguaranteedtobetrueandONE.compareTo(TWO)isguaranteedtobelessthanone.C.TheExamplevaluescannotbeusedinarawjava.util.HashMap.；instead，theprogrammermustuseajava.util.EnumMap.D.TheExamplevaluescanbeusedinajava.util.SortedSet，butthesetwillNOTbesortedbecauseenumeratedTypedoNOTIMPLEMENTjava.lang.Comparable.Answer：(A)A對(duì)的B不能保證C錯(cuò)誤枚舉類(lèi)型元素是可以用在HASHMAP里HashMap<Integer，Example>h=newHashMap<Integer，Example>;h.put(1，Example.ONE);D錯(cuò)誤，枚舉類(lèi)型元素值是可以放入SortedSet里例如TreeSet.把枚舉類(lèi)型元素轉(zhuǎn)成字符串在放入其中，字符串就已經(jīng)實(shí)現(xiàn)comparable接口。可以自然排序。SortedSet<Example>s=newTreeSet<Example>();s.add(Example.TWO);s.add(Example.ONE);System.out.println(s);打印出成果[ONE，TWO]QUESTION74Giventheexhibit：WhichlineofcodemarkstheearliestpointthatanobjectreferencedbyintObjbecomesacandidateforgarbagecollection?A.Line16B.Line17C.Line18D.Line19E.TheobjectisNOTacandidateforgarbagecollection.Answer：(D)intObj始終會(huì)被numbers引用，直到19行之后QUESTION75Given：Andthecommandlineinvocation：javaYippee2abcWhatistheresult?A.abB.bcC.abcD.Compilationfails.E.Anexceptionisthrownatruntime.Answer：(B)QUESTION76Aclassgames.cards.PokeriscorrectlydefinedinthejarfilePoker.jar.AuserwantstoexecutethemainmethodofPokeronaUNIXsystemusingthecommand：Javagames.cards.PokerWhatallowstheusertodothis?A.putPoker.jarindirectory/stuff/java，andsettheCLASSPATHtoinclude/stuff/javaB.putPoker.jarindirectory/stuff/java，andsettheCLASSPATHtoinclude/stuff/java/*.jarC.putPoker.jarindirectory/stuff/java，andsettheCLASSPATHtoinclude/stuff/java/Poker.jarD.putPoker.jarindirectory/stuff/java/games/cards，andsettheCLASSPATHtoinclude/stuff/javaE.putPoker.jarindirectory/stuff/java/games/cards，andsettheCLASSPATHtoinclude/stuff/java/*.jarF.putPoker.jarindirectory/stuff/java/games/cards，andsettheCLASSPATHtoinclude/stuff/java/Poker.jarAnswer：(C)classpath中須明確寫(xiě)明poker.jar，不能用*.jarQUESTION77Whichthreecodefragments，addedindividuallyatline29，producetheoutput100?(Choosethree.)A.n=100；B.i.setX(100)；C.o.getY().setX(100)；D.i=newInner()；i.setX(100)；E.0.setY(i)；i=newInner()；i.setX(100)；F.i=newInner()；i.setX(100)；o.setY(i)；Answer：(B，C，F(xiàn))依照內(nèi)存關(guān)系可知QUESTION78GivenaclassRepetition：AndgivenanotherclassDemo：Whichcodeshouldbeinsertedatline1ofDemo.javatocompileandrunDemotoprint"pizzapizza"A.importutils.*；B.staticimportutils.*；C.importutils.Repetition.*；D.staticimportutils.Repetition.*；E.importutils.Repetition.twice()；F.importstaticutils.Repetition.twice；G.staticimportutils.Repetition.twice;Answer：(F)靜態(tài)import引入靜態(tài)辦法.importstaticutils..Repetition*；或者importstaticutils.Repetition.twice;A 正常導(dǎo)入類(lèi),Demo第5行要new實(shí)例才干帶用twice辦法.B staticimport順序顛倒,并且要加上class名C 正常導(dǎo)入,類(lèi)名背面不能跟*D 順序顛倒E 正常導(dǎo)入,只能導(dǎo)入包下類(lèi),不能導(dǎo)入類(lèi)里辦法.G 順序顛倒QUESTION79Given：Andtheinvocation：Whatistheresult?A.Anexceptionisthrownatruntime.B."Stringisempty"isprintedtooutput.C.Compilationfailsbecauseofanerrorinline12.D."Stringisnotempty"isprintedtooutput.Answer：(A)A空指針異常------------------“|”是非短路邏輯運(yùn)算符QUESTION80Exhibit:Giventhefully-qualifiedclassnames：com.foo.bar.Dogcom.foo.bar.blatz.Bookcom.bar.Carcom.bar.blatz.SunWhichgraphrepresentsthecorrectdirectorystructureforaJARfilefromwhichthoseclassescanbeusedbythecompilerandJVM?A.JarAB.JarBC.JarCD.JarDE.JarEAnswer：(A)QUESTION81Given：andtwoseparatecommandlineinvocations：javaYippeejavaYippee1234Whatistheresult?Nooutputisproduced.123B. Nooutputisproduced.234C. Nooutputisproduced.1234D. Anexceptionisthrownatruntime.123E. Anexceptionisthrownatruntime.234F. Anexceptionisthrownatruntime.1234Answer：(B)QUESTION82Given：Whatistheresult?A.CompilationfailsB.AnexceptionisthrownatruntimeC.doStuffx=6mainx=6D.doStuffx=5mainx=5E.doStuffx=5mainx=6F.doStuffx=6mainx=5Answer：(D)第10行參數(shù)x是值傳遞，不會(huì)變化main中x值。QUESTION83Given:WhenthedoSomethingmethodiscalled，afterwhichlinedoestheObjectcreatedinline5becomeavailableforgarbagecollection?A.Line5B.Line6C.Line7D.Line8E.Line9F.Line10Answer：(D)棧內(nèi)存用來(lái)存儲(chǔ)基本類(lèi)型變量和對(duì)象引用變量(對(duì)象地址)堆內(nèi)存用來(lái)存儲(chǔ)由new創(chuàng)立對(duì)象和數(shù)組QUESTION84Given：Whatistheresult?A. ExceptionB. A，B，ExceptionC. Compilationfailsbecauseofanerrorinline20.D. Compilationfailsbecauseofanerrorinline14.E. ANullPointerExceptionisthrownatruntime.Answer：(D)改寫(xiě)規(guī)定,子類(lèi)拋出異常要比父類(lèi)異常要小.本題中父類(lèi)沒(méi)有異常,子類(lèi)也不能有異常.QUESTION85Given:Whatistheresult?A.harrierB.shepherdC.retrieverD.CompilationfailsE.retrieverharrierF.Anexceptionisthrownatruntime.Answer：(D)18行，casedefault：語(yǔ)法錯(cuò)誤，應(yīng)改成default:QUESTION86Given：Whatistheresult?A. A，B，CB. B，C，AC. CompilationfailsD. ThecoderunswithnooutputE. AnexceptionisthrownatruntimeAnswer：(B)LinkedList有順序性，QUESTION87GivenWhatistheresult?A.endB.CompilationfailsC.exceptionendD.exceptiontestendE.AThrowableisthrownbymainF.AnExceptionisthrownbymainAnswer：(E)16行拋出Error，沒(méi)有捕獲。Throwable，Error和Exception都是她子類(lèi)QUESTION88Given：Whichthree，willmakecodeon37executeA.Theinstancegetsgarbagecollected.B.Thecodeonline33throwsanexception.C.Thecodeonline35throwsanexception.D.Thecodeonline31throwsanexception.E.Thecodeonline33executessuccessfully.Answer：(B，C，E)QUESTION89Given:Whatistheresult?A.CompilationfailsB.piisbiggerthan3.C.Anexceptionoccursatruntime.D.piisbiggerthan3.Haveaniceday.E.piisnotbiggerthan3.Haveaniceday.Answer：(A)18行finally是配合try使用.QUESTION90Given：Whichcode，insertedatline16willcauseajava.lang.ClassCastException?A.Alphaa=x；B.Foof=(Delta)x；C.Foof=(Alpha)x；D.Betab=(Beta)(Alpha)x;Answer：(B)轉(zhuǎn)到子類(lèi)別拋異常。.QUESTION91Givenamethodthatmustensurethatitsparameterisnotnull：What，insertedatline12，istheappropriatewaytohandleanullvalue?A.assertvalue==null；B.assertvalue!=null，"valueisnull"；C.if(value==null){thrownewAssertionException("valueisnull")；}D.if(value==null){thrownewIllegalArgumentException("valueisnull")；}Answer：(D)A 不要用斷言對(duì)公共辦法參數(shù)進(jìn)行判斷B 同上C 沒(méi)有AssertionException這個(gè)類(lèi)；AssertionError繼承自Error，handleerror是沒(méi)故意義D OK拋出參數(shù)錯(cuò)誤異常.QUESTION92PlacethecorrectCodeintheCodeSampletoachievetheexpectedresults.Expectedresults：Output：12481632CodeSampleAnswer：()for(intx：y){QUESTION93Given：WhichtwowillproduceanAssertionError?(Choosetwo.)A.javatestB.java-eatestC.javatestfile1D.java-eatestfile1E.java-eatestfile1file2F.java–ea：testtestfile1Answer：(B，E)QUESTION94Given：WhichstatementistrueifaResourceExceptionisthrownonline86?A.Line92willnotexecute.B.Theconnectionwillnotberetrievedinline85.C.Theresourceconnectionwillnotbeclosedonline88. D.Theenclosingmethodwillthrowanexceptiontoitscaller.Answer：(C)QUESTION95AssumingthattheserializeBanana()andthedeserializeBanana()methodswillcorrectlyuseJavaserializationandgiven：Whatistheresult?A.restore400B.restore403C.restore453D.Compilationfails.E.Anexceptionisthrownatruntime.Answer：(C)QUESTION96Given：Whatistheresult?A.CompilationfailsB.Piisapproximately3.C.Piisapproximately3.141593.D.Anexceptionisthrownatruntime.Answer：(D)%d打印一種整數(shù)，規(guī)定接受一種整數(shù)拋IllegalFormatConversionExceptionQUESTION97Given：Whatistheresult?A.intLongB.ShortLongC.CompilationfailsD.Anexceptionisthrownatruntime.Answer：(A)QUESTION98Chaintheseconstructorstocreateobjectstoreadfromafilenamed"in"andtowritetoafilenamed"out".Answer：()newBufferedReader(newFileReader(“in”));newPrintWriter(newBufferedWriter(newFileWriter(“out”)));QUESTION99PlacethecodefragmentsintopositiontouseaBufferedReadertoreadinanentiretextfile.Answer：()classPrintFile{ publicstaticvoidmain(String[]args){ BufferedReaderbuffReader=null; //morecodeheretoinitializebuffReader try{ Stringtemp; while((temp=buffReader.readLine())!=null){ System.out.println(temp); } }catch(IOExceptione){ e.printStackTrace(); } }}QUESTION100Giventhismethodinaclass：Whichstatementistrue?A.ThiscodeisNOTthread-safe.B.TheprogrammercanreplaceStringBufferwithStringBuilderwithnootherchanges.C.Thiscodewillperformpoorly.Forbetterperformance，thecodeshouldberewritten：return"<"++">"；D.ThiscodewillperformwellandconvertingthecodetouseStringBuilderwillnotenhancetheperformance.Answer：(B)QUESTION101Given：WhatcreatestheappropriateDateFormatobjectandaddsadaytotheDateobject?A. 35.Dateformatdf=Dateformat.getDateFormat()；42.d.setTime((60*60*24)+d.getTime())；B. 35.Dateformatdf=Dateformat.getDateInstance()；42.d.setTime((1000*60*60*24)+d.getTime())；C. 35.Dateformatdf=Dateformat.getDateFormat()；42.d.setLocalTime((1000*60*60*24)+d.getLocalTime())；D. 35.Dateformatdf=Dateformat.getDateInstance()；42.d.setLocalTime((60*60*24)+d.getLocalTime());Answer：(B)轉(zhuǎn)換成求加1天后來(lái)改日期毫秒數(shù)，再調(diào)用setTime()設(shè)立時(shí)間QUESTION102Given：WhichtwostatementsaretrueabouttheresultifthelocaleisLocale.US?(Choosetwo.)A.Thevalueofbis2.B.Thevalueofais3.14.C.Thevalueofbis2.00.D.Thevalueofais3.141.E.Thevalueofais3.1415.F.Thevalueofais3.1416.G.Thevalueofbis2.0000.Answer：(C，F(xiàn))QUESTION103Placethecorrectdescriptionofthecompileroutputonthecodefragmenttobeinsertedatline4and5.Thesamecompileroutputmaybeusedmorethanonce.Answer：()QUESTION104Given：Whichthreewillcompilesuccessfully?(Choosethree.)A.Objecto=Old.get0(newLinkedList())；B.Objecto=Old.get0(newLinkedList<?>())；C.Strings=Old.get0(newLinkedList<String>())；D.Objecto=Old.get0(newLinkedList<Object>());E.Strings=(String)Old.get0(newLinkedList<String>());Answer：(A，D，E)B錯(cuò)誤<?>不應(yīng)出當(dāng)前這里C錯(cuò)誤get0()辦法回傳值是Object，因而不可賦值給StringQUESTION105Exhibit：Whichstatementistrueaboutthesetvariableonline12?A.Thesetvariablecontainsallsixelementsfromthecollcollection，andtheorderisguaranteedtobepreserved.B.Thesetvariablecontainsonlythreeelementsfromthecollcollection，andtheorderisguaranteedtobepreserved.C.Thesetvariablecontainsallsixelementsfromthecollcollection，buttheorderisNOTguaranteedtobepreserved.D.Thesetvariablecontainsonlythreeelementsfromthecollcollection，buttheorderisNOTguaranteedtobepreserved.Answer：(D)Set中元素是不能重復(fù)，沒(méi)有順序QUESTION106Given：WhatistheappropriateddefinitionofthehashCodemethodinclassPerson?A.returnsuper.hashCode()；B.returnname.hashCode()+age*7;C.returnname.hashCode()+comment.hashCode()/2；D.returnname.hashCode()+comment.hashCode()/2-age*3；Answer：(B)兩個(gè)equals對(duì)象，hashCode()應(yīng)當(dāng)相等，equals中是判斷age和name相等，因此hashCode也用age和name計(jì)算，A，C，D也許導(dǎo)致兩個(gè)相等對(duì)象，hashCode不相等QUESTION107Given：Whichstatementistrue?A.TheequalsmethoddoesNOTproperlyoverridetheObject.equalsmethod.B.Compilationfailsbecausetheprivateattributecannotbeaccessedinline5.C.Toworkcorrectlywithhash-baseddatastructures，thisclassmustalsoimplementthehashCodemethod.D.WhenaddingPersonobjectstojava.util.Setcollection，theequalsmethodinline4willpreventduplicates.Answer：(A)QUESTION108Given：Whichcode，insertedatline4，guaranteesthatthisprogramwilloutput[1，2]?A.Setset=newTreeSet()；B.Setset=newHashSet()；C.Setset=newSortedSet()；D.Listset=newSortedList()；E.Setset=newLinkedHashSet();Answer：(A)TreeSet可自動(dòng)排序，SortedSet是接口，不能實(shí)例化QUESTION109Given：What，insertedatline39，willsortthekeysinthepropsHashMap?A.Array.sort(s)；B.s=newTreeSet(s)；C.Collections.sort(s)；D.s=newSortedSet(s)；Answer：(B)QUESTION110Placecodeintotheclasssothatitcompilesandgeneratestheoutputanswer=42.Note：Codeoptionsmaybeusedmorethanonce.Answer：()publicclassGen<T>{ privateTobject; publicGen(Tobject){ this.object=object;}publicTgetObject(){ returnobject;}…}QUESTION111----------------???第一選項(xiàng)解釋Given：PlacetheCompilationResultsoneachcodestatementtoindicatewhetherornotthatcodewillcompileifinsertedintothetakeList()method.Answer：()List<String>StrList=newArrayList<String>();List<Integer>IntList=newArrayList<Integer>();List<?extendsObject>list;//該類(lèi)型泛型之能接受對(duì)象賦值,不能直接對(duì)該對(duì)象進(jìn)行add操作.//list.add(newObject());list=StrList;list=IntList;QUESTION112WhichtwocodefragmentswillexecutethemethoddoStuff()inaseparatethread?(Choosetwo.)A. newThread(){publicvoidrun(){doStuff();}}；B. newThread(){publicvoidstart(){doStuff();}}；C. newThread(){publicvoidstart(){doStuff();}}.run()；D. newThread(){publicvoidrun(){doStuff()；}}.start()；E. newThread(newrunnable(){publicvoidrun(){doStuff()；}}).run()；F. newThread(newrunnable(){publicvoidrun(){doStuff()；}}).start();Answer：(D，F(xiàn))D匿名類(lèi)別中復(fù)寫(xiě)run辦法，并調(diào)用start()辦法啟動(dòng)線程F運(yùn)用匿名實(shí)現(xiàn)runnable接口中run辦法，并調(diào)用start()啟動(dòng)線程QUESTION113Given：Whichtocanberesults?(Choosetwo.)A. java.lang.RuntimeException：ProblemB. run.java.lang.RuntimeException：ProblemC. Endofmethod.java.lang.RuntimeException：ProblemD. Endofmethod.run.java.lang.RuntimeException：ProblemE. run.java.lang.RuntimeException：ProblemEndofmethodAnswer：(D、E)在t中拋出RuntimeException，不干擾主線程執(zhí)行；QUESTION114----Given：Whichthreechangesshouldbemadetoadaptthisclasstobeusedsafelybymultiplethreads?(Choosethree.)A.declarereset()usingthesynchronizedkeywordB.declaregetName()usingthesynchronizedkeywordC.declaregetCount()usingthesynchronizedkeywordD.declaretheconstructorusingthesynchronizedkeywordE.declareincrement()usingthesynchronizedkeywordAnswer：(A，C，E)D選項(xiàng)錯(cuò)誤，由于構(gòu)造辦法不能用synchronized修飾name是final變量不會(huì)有多線程上維護(hù)問(wèn)題QUESTION115Given：Whichstatementistrue?A.CompilationfailsB.Anexceptionisthrownatruntime.C.Synchronizingtherun()methodwouldmaketheclassthread-safe.D.Thedatainvariable"x"areprotectedfromconcurrentaccessproblems.E.DeclaringthedoThings()methodasstaticwouldmaketheclassthread-safe.F.WrappingthestatementswithindoThings()inasy