2023年SCJP认证考试题库

QUESTION61GIVENTHEEXHIBIT:Whichstatementistrue?A.Alloftheassertstatementsareusedappropriately.B.Onlytheassertstatementonline31isusedappropriatelyC.Theassertstatementsonlines29and31areusedappropriatelyD.Theassertstatementsonlines26and29areusedappropriatelyE.Theassertstatementsonlines29and33areusedappropriatelyF.Theassertstatementsonlines29,31and33areusedappropriatelyG.Theassertstatementsonlines26,29and31areusedappropriately断言应当用在“你认为”你的程序不也许产生错误的地方，并且有没有启用断言，都不会影响程序的正常运营。断言使用限制：不要在public方法中，用断言来检查参数的对的性；不要让断言语句去解决一些程序必须的流程。因素：1.public方法会被别人调用，你不能保证他一定启用断言；假如没有启用，那么用断言来做参数的检查也就没故意义了。所以不要用断言来检查参数，公共方法的参数一定要用代码执行检查； 2.假如用断言来控制程序执行流程，假如没有启用断言，那么程序就不能对的执行下去。此外，断言语句不可以有任何边界效应，不要使用断言语句去修改变量和改变方法的返回值，假如这样当启动断言和不启动断言执行的结果会截然不同。断言的使用时机：检查流程的不变性：在if-elseswitch-case的预期结果之外可以加上断言做额外的检查。内部执行的不变性：if(true){return;}assertfalse;检查私有方法的参数，结果等程序运营中的一致性断言语句不是永远会执行，可以屏蔽也可以启用

javac–source1.4*.java需要java–ea启用assert；当判断条件为FALSE时就抛犯错误。Answer:(C)26行不合适：不要对public方法的参数断言29合适：程序员在程序中最不大也许到达的地方断言

31合适：断言private方法的参数

33行不合适：启用和不启用断言会产生不同的程序执行序

参考大纲：异常解决—断言和AssertionErrorQUESTION62GIVENTHEEXHIBIT:Whatistheresult?A. nullB. zeroC. someD. CompilationfailsE. AnexceptionisthrownatruntimeAnswer:(D)13行会报错，应在15行使用elseif参考大纲：流程控制QUESTION63Giventheexhibit:Whatistheresult?A.testB.ExceptionC.CompilationfailsD.NullPointerExceptionAnswer:(C)18行犯错，应当先catch子异常，再catchException；13行把args赋null，14行会报NullPointerException假如没有第13行运营时14行会报ArrayIndexOutOfBoundsException异常。参考大纲：异常解决QUESTION64Giventheexhibit:Whatistheresult?A.CompilationfailsB.aAaAaAaAAaaAaAC.AAaaAaAaAaaAaAD.AaAAAaaaAaAaAaE.aAaAaAaAaAAAaaF.AnexceptionisthrownatruntimeAnswer:(C)第10行将对strings这个集合做自然排序(ASCII小到大，一个一个比较)Collections.sort(Listlist)对list进行排序，对set不能排序！List里可以放对象，所以当list里面存放的是对象的时候就不能用Collections.sort(Listlist)去排序了。由于JVM不知道用什么规则去排序！！只有把对象类实现Comparable接口，然后改写compareTo()参考大纲：集合QUESTION65Giventheexhibit:Whatistheresult?A.0B.1C.2D.3E.4F.Compilationfails.G.AnexceptionisthrownatruntimeAnswer:(D)Set中存放的元素是无序不反复的。假如你想Set里Add一个元素，一方面他会去调用equals方法，判断set中是否有该元素，假如有则不更改set的值并返回false，假如没有，则把元素添加进去，并返回true。Ws1ws2是自定义的类，ws1和ws2equals不相等；String的equals方法已经改写，s1和s2相等；比较两个对象是否相同,先比较hashcode,假如相同,在用equals方法比较.假如都相同则两个对象就认为是相同的.Hashcode是把对象的内存地址通过运算得来的.基本数据类型和基本数据类型的包装类尚有String类都已经覆盖了hashcode(),equals(),所以这些对象的值只要同样就认为对象同样.参考大纲：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)publicstaticintsum(List<Integer>intList){intsum=0;for(inti:intList){ sum+=i;}returnsum;}参考大纲：集合和泛型Whatistheresult?A.Compilationfailsduetoanerrorinline23.B.Compilationfailsduetoanerrorinline29.C.AClassCastExceptationoccursinline29.D.AClassCastExceptationoccursinline31.E.Thevalueofallfourobjectprintsinnaturalorder.Answer:(C)Arrays.sort(Object[]a)方法中，a的每一个元素都必须是互相可以比较的（调用pareTo(Objecto2)）。否则会报ClassCastException的异常。参考大纲：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泛型规范没问题m2(listA)Compilesandrunswithouterror泛型规范没问题m1(listB)CompilesandrunswithouterrorB是A的子类，泛型规范没问题m2(listB)Doesnotcompilem1(listO)Doesnotcompilem2(listO)DoesnotcompileQUESTION70Giventheexhibit:Whatistheresult?A.apple:appleB.carrot:appleC.apple:bananaD.banana:appleE.carrot:carrotF.carrot:bananaAnswer:(C)PriorityQueue优先级队列：预设是自然排序，因此pq内的元素顺序将是apple->banana->carrotpoll()取第一个元素，取完之后删除，peek取第一个元素，并不删除元素QUESTION71Given:AprogrammerisdevelopingaclassKey,thatwillbeusedasakeyinastandardjava.util.HashMap.Whichtwomethodsshouldbeoverriddentoassurethatkeyworkscorrectlyasakey?(choosetwo)A.publicinthashCode()B.publicBooleanequals(Keyk)C.publicintcompareTo(Objecto)D.publicBooleanequals(Objecto)Answer:(A,D)HashMap中的key不能反复，因此必须实现hashCode和equals方法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)N是泛型类别变量，它相称于一个类型。A 类声明是不能用？这个万用字符。B 同上C Object没有doubleValue()方法。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对的B不能保证C错误枚举类型的元素是可以用在HASHMAP里的HashMap<Integer,Example>h=newHashMap<Integer,Example>;h.put(1,Example.ONE);D错误，枚举类型的元素值是可以放入SortedSet里的例如TreeSet.把枚举类型的元素转成字符串在放入其中，字符串就已经实现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);打印出结果[ONE,TWO]QUESTION74Giventheexhibit:WhichlineofcodemarkstheearliestpointthatanobjectreferencedbyintObjbecomesacandidateforgarbagecollection?A.Line16B.Line17C.Line18D.Line19E.TheobjectisNOTacandidateforgarbagecollection.Answer:(D)intObj一直会被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中须明确写明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)根据内存关系可知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)静态import引入静态方法.importstaticutils..Repetition*;或者importstaticutils.Repetition.twice;A 正常的导入类,Demo的第5行要new实例才干带用twice方法.B staticimport顺序颠倒,并且要加上class名C 正常的导入,类名后面不能跟*D 顺序颠倒E 正常的导入,只能导入包下的类,不能导入类里的方法.G 顺序颠倒QUESTION79Given:Andtheinvocation:Whatistheresult?A.Anexceptionisthrownatruntime.B."Stringisempty"isprintedtooutput.C.Compilationfailsbecauseofanerrorinline12.D."Stringisnotempty"isprintedtooutput.Answer:(A)A空指针异常------------------“|”是非短路逻辑运算符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行参数x是值传递，不会改变main中x的值。QUESTION83Given:WhenthedoSomethingmethodiscalled,afterwhichlinedoestheObjectcreatedinline5becomeavailableforgarbagecollection?A.Line5B.Line6C.Line7D.Line8E.Line9F.Line10Answer:(D)栈内存用来存放基本类型的变量和对象的引用变量(对象的地址)堆内存用来存放由new创建的对象和数组QUESTION84Given:Whatistheresult?A. ExceptionB. A,B,ExceptionC. Compilationfailsbecauseofanerrorinline20.D. Compilationfailsbecauseofanerrorinline14.E. ANullPointerExceptionisthrownatruntime.Answer:(D)改写的规定,子类抛出的异常要比父类的异常要小.本题中父类没有异常,子类也不能有异常.QUESTION85Given:Whatistheresult?A.harrierB.shepherdC.retrieverD.CompilationfailsE.retrieverharrierF.Anexceptionisthrownatruntime.Answer:(D)18行，casedefault:语法错误，应改成default:QUESTION86Given:Whatistheresult?A. A,B,CB. B,C,AC. CompilationfailsD. ThecoderunswithnooutputE. AnexceptionisthrownatruntimeAnswer:(B)LinkedList有顺序性，QUESTION87GivenWhatistheresult?A.endB.CompilationfailsC.exceptionendD.exceptiontestendE.AThrowableisthrownbymainF.AnExceptionisthrownbymainAnswer:(E)16行抛出Error,没有捕获。Throwable，Error和Exception都是他的子类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使用的.QUESTION90Given:Whichcode,insertedatline16willcauseajava.lang.ClassCastException?A.Alphaa=x;B.Foof=(Delta)x;C.Foof=(Alpha)x;D.Betab=(Beta)(Alpha)x;Answer:(B)转到子类别抛异常。.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 不要用断言对公共方法的参数进行判断B 同上C 没有AssertionException这个类;AssertionError继承自Error，handleerror是没故意义的D OK抛出参数错误的异常.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打印一个整数，规定接受一个整数抛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)转换成求加1天以后改日期的毫秒数，再调用setTime()设立时间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)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错误<?>不应出现在这里C错误get0()方法的回传值是Object,因此不可赋值给StringQUESTION105Exhibit:Whichstatementistrueaboutthesetvariableonline12?A.Thesetvariablecontainsallsixelementsfromthecollcollection,andtheorderisguaranteedtobepreserved.B.Thesetvariablecontainsonlythreeelementsfromthecollcollection,andtheorderisguaranteedtobepreserved.C.Thesetvariablecontainsallsixelementsfromthecollcollection,buttheorderisNOTguaranteedtobepreserved.D.Thesetvariablecontainsonlythreeelementsfromthecollcollection,buttheorderisNOTguaranteedtobepreserved.Answer:(D)Set中元素是不能反复，没有顺序的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)两个equals的对象，hashCode()应当相等，equals中是判断age和name相等，所以hashCode也用age和name计算，A,C,D也许导致两个相等的对象，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可自动排序，SortedSet是接口，不能实例化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----------------???第一选项解释Given:PlacetheCompilationResultsoneachcodestatementtoindicatewhetherornotthatcodewillcompileifinsertedintothetakeList()method.Answer:()List<String>StrList=newArrayList<String>();List<Integer>IntList=newArrayList<Integer>();List<?extendsObject>list;//该类型的泛型之能接受对象赋值,不能直接对该对象进行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)D匿名类别中复写run方法，并调用start()方法启动线程F运用匿名实现runnable接口中的run方法，并调用start()启动线程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中抛出RuntimeException，不干扰主线程的执行；QUESTION114----Given:Whichthreechangesshouldbemadetoadaptthisclasstobeusedsafelybymultiplethreads?(Choosethree.)A.declarereset()usingthesynchronizedkeywordB.declaregetName()usingthesynchronizedkeywordC.declaregetCount()usingthesynchronizedkeywordD.declaretheconstructorusingthesynchronizedkeywordE.declareincrement()usingthesynchronizedkeywordAnswer:(A,C,E)D选项错误，由于构造方法不能用synchronized修饰name是final变量不会有多线程上维护的问题QUESTION115Given:Whichstatementistrue?A.CompilationfailsB.Anexceptionisthrownatruntime.C.Synchronizingtherun()methodwouldmaketheclassthread-safe.D.Thedatainvariable"x"areprotectedfromconcurrentaccessproblems.E.DeclaringthedoThings()methodasstaticwouldmaketheclassthread-safe.F.WrappingthestatementswithindoThings()i