core java: best practices and bytecodes quiz

QuizA fun way to learn more!

Withcontributionsfrom:• Manjunathan• Vaibhav• Ganesh

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QuestionWhatquerylanguagedoesElasticsearch use?

A.SQLB.QueryDSLC.QuerySSLD.ElasticClient

AnswerWhatquerylanguagedoesElasticsearch use?

A.SQLB.QueryDSLC.QuerySSLD.ElasticClient

ExplanationB.QueryDSL- QueryDSLisElasticsearch’snativeQueryDomainSpecificLanguage(DSL)

QuestionInElasticsearch,whichfiltercanbeusedtocombinemultiplefilters?

A.termB.rangeC.existsD.bool

AnswerInElasticsearch,whichfiltercanbeusedtocombinemultiplefilters?

A.termB.rangeC.existsD.bool

ExplanationD.bool,whichisusedtocombinemultiplefiltersusingmust/should

QuestionInElasticsearch,"Synonym"isanexampleof:

A.tokenizerB.analyzerC.tokenfilterD.characterfilter

AnswerInElasticsearch,"Synonym"isanexampleof:

A.tokenizerB.analyzerC.tokenfilterD.characterfilter

ExplanationC.Tokenfilter

Hereistheusageof“synonym”tofilterbasedon“synonyms”example:

QuestionWhatwillbethebehavior ofrunning:

java-server-clientHelloWorld

A. Error.B. ItwillrunintheservermodeC. ItwillrunintheclientmodeD. Can'tguess!

AnswerWhatwillbethebehavior ofrunning:

java-server-clientHelloWorld

A. Error.B. ItwillrunintheservermodeC. ItwillrunintheclientmodeD. Can'tguess!

QuestionHowarelambdaexpressionstranslatedbytheJavacompilerandexecutedbytheJVM?

A.LambdaexpressionsaretranslatedtoanonymousclassesB.Compilertranslatesto“invokedynamic”methodinstructionC.Compilertranslatesto“invokevirtual”methodinstructionD.Compilertranslatesto“invokestatic”methodinstruction

AnswerHowarelambdaexpressionstranslatedbytheJavacompilerandexecutedbytheJVM?

A.LambdaexpressionsaretranslatedtoanonymousclassesB.Compilertranslatesto“invokedynamic”methodinstructionC.Compilertranslatesto“invokevirtual”methodinstructionD.Compilertranslatesto“invokestatic”methodinstruction

QuestionWhichofthefollowingwasNOTintroducedinJavaversion8?

A. LambdafunctionsB. StreamsAPIC. invokedynamic methodinstructionD. Joda libraryasdate/timeAPI

AnswerWhichofthefollowingwasNOTintroducedinJavaversion8?

A. LambdafunctionsB. StreamsAPIC. invokedynamic methodinstructionD. Joda libraryasdate/timeAPI

ExplanationC.invokedynamic methodinstruction

Lambdafunctions,streamsAPI,andJoda libraryasdate/timeAPIwereintroducedinJavaversion8.

Theinvokedynamic methodinstructionwasintroducedinJava7.

[WhenfunctionalprogrammingsupportwasaddedintheformoflambdafunctionswasaddedinJava8,thecompilerandJVMwereenhancedtouseinvokedynamicinstruction.]

Questionclass Base{}class DeriOne extends Base{}class DeriTwo extends Base{}

class ArrayStore {publicstaticvoidmain(String[]args){

Base[]baseArr =new DeriOne[3];baseArr[0]=new DeriOne();baseArr[2]=new DeriTwo();System.out.println(baseArr.length);

}}

A.Thisprogramprintsthefollowing:3B.Thisprogramprintsthefollowing:2C.ThisprogramthrowsanArrayStoreExceptionD.ThisprogramthrowsanArrayIndexOutOfBoundsException

Answerclass Base{}class DeriOne extends Base{}class DeriTwo extends Base{}

class ArrayStore {publicstaticvoidmain(String[]args){

Base[]baseArr =new DeriOne[3];baseArr[0]=new DeriOne();baseArr[2]=new DeriTwo();System.out.println(baseArr.length);

}}

A.Thisprogramprintsthefollowing:3B.Thisprogramprintsthefollowing:2C.ThisprogramthrowsanArrayStoreExceptionD.ThisprogramthrowsanArrayIndexOutOfBoundsException

ExplanationC.ThisprogramthrowsanArrayStoreException

ThevariablebaseArrisoftypeBase[],anditpointstoanarrayoftypeDeriOne.

However,inthestatementbaseArr[2]=newDeriTwo(),anobjectoftypeDeriTwoisassignedtothetypeDeriOne,whichdoesnotshareaparent-childinheritancerelationship-theyonlyhaveacommonparent,whichisBase.Hence,thisassignmentresultsinanArrayStoreException.

Discussion:Whatisthebestpracticehere?

Questionimportjava.util.*;

class UtilitiesTest {public static voidmain(String[]args){

List<Integer>intList =new LinkedList<>();List<Double>dblList =new LinkedList<>();System.out.println(intList.getClass()==dblList.getClass());

}}

A.Itprints:trueB.Itprints:falseC.ItresultsinacompilererrorD.Itresultsinaruntimeexception

Answerimportjava.util.*;

class UtilitiesTest {public static voidmain(String[]args){

List<Integer>intList =new LinkedList<>();List<Double>dblList =new LinkedList<>();System.out.println(intList.getClass()==dblList.getClass());

}}

A.Itprints:trueB.Itprints:falseC.ItresultsinacompilererrorD.Itresultsinaruntimeexception

ExplanationA.Itprints:true

Duetotypeerasure,aftercompilationbothtypesaretreatedassameLinkedListtype.

Firsttype:classjava.util.LinkedListSecondtype:classjava.util.LinkedList


QuestionConsiderthefollowingprogram:

class AutoCloseableTest {public static void main(String[]args){

try (ScannerconsoleScanner =new Scanner(System.in)){consoleScanner.close();//CLOSEconsoleScanner.close();

}}

}

Whichoneofthefollowingstatementsiscorrect?A.ThisprogramterminatesnormallywithoutthrowinganyexceptionsB.ThisprogramthrowsanIllegalStateExceptionC.ThisprogramthrowsanIOExceptionD.ThisprogramthrowsanAlreadyClosedExceptionE.ThisprogramresultsinacompilererrorinthelinemarkedwiththecommentCLOSE

AnswerConsiderthefollowingprogram:

class AutoCloseableTest {public static void main(String[]args){

try (ScannerconsoleScanner =new Scanner(System.in)){consoleScanner.close();//CLOSEconsoleScanner.close();

}}

}

Whichoneofthefollowingstatementsiscorrect?A.ThisprogramterminatesnormallywithoutthrowinganyexceptionsB.ThisprogramthrowsanIllegalStateExceptionC.ThisprogramthrowsanIOExceptionD.ThisprogramthrowsanAlreadyClosedExceptionE.ThisprogramresultsinacompilererrorinthelinemarkedwiththecommentCLOSE

ExplanationA.Thisprogramterminatesnormallywithoutthrowinganyexceptions.

Thetry-with-resourcesstatementinternallyexpandstocalltheclose()methodinthefinallyblock.Iftheresourceisexplicitlyclosedinthetryblock,thencallingclose()againdoesnothaveanyeffect.Fromthedescriptionoftheclose()methodintheAutoCloseable interface:“Closesthisstreamandreleasesanysystemresourcesassociatedwithit.Ifthestreamisalreadyclosed,theninvokingthismethodhasnoeffect.”


QuestionTherearetwokindsofstreamsinthejava.iopackage:characterstreams(i.e.,thosederivingfromReaderandWriterinterfaces)andbytestreams(i.e.,thosederivingfromInputStream andOutputStream).Whichofthefollowingstatementsistrueregardingthedifferencesbetweenthesetwokindsofstreams?

A.Incharacterstreams,dataishandledintermsofbytes;inbytestreams,dataishandledintermsofUnicodecharacters.B.Characterstreamsaresuitableforreadingorwritingtofilessuchasexecutablefiles,imagefiles,andfilesinlow-levelfileformatssuchas.zip,.classC.Bytestreamsaresuitableforreadingorwritingtotext-basedI/Osuchasdocumentsandtext,XML,andHTMLfiles.D.Bytestreamsaremeantforhandlingbinarydatathatisnothuman-readable;characterstreamsaremeantforhuman-readablecharacters.

AnswerTherearetwokindsofstreamsinthejava.iopackage:characterstreams(i.e.,thosederivingfromReaderandWriterinterfaces)andbytestreams(i.e.,thosederivingfromInputStream andOutputStream).Whichofthefollowingstatementsistrueregardingthedifferencesbetweenthesetwokindsofstreams?

A.Incharacterstreams,dataishandledintermsofbytes;inbytestreams,dataishandledintermsofUnicodecharacters.B.Characterstreamsaresuitableforreadingorwritingtofilessuchasexecutablefiles,imagefiles,andfilesinlow-levelfileformatssuchas.zip,.classC.Bytestreamsaresuitableforreadingorwritingtotext-basedI/Osuchasdocumentsandtext,XML,andHTMLfiles.D.Bytestreamsaremeantforhandlingbinarydatathatisnothuman-readable;characterstreamsaremeantforhuman-readablecharacters.

ExplanationD.Bytestreamsaremeantforhandlingbinarydatathatisnothumanreadable;characterstreamsareforhuman-readablecharacters.

Incharacterstreams,dataishandledintermsofUnicodecharacters,whereasinbytestreams,dataishandledintermsofbytes.Bytestreamsaresuitableforreadingorwritingtofilessuchasexecutablefiles,imagefiles,andfilesinlow-levelfileformatssuchas.zip,.class,and.jar.Characterstreamsaresuitableforreadingorwritingtotext-basedI/Osuchasdocumentsandtext,XML,andHTMLfiles.


QuestionWhichoneofthefollowingoptionsisbestsuitedforgeneratingrandomnumbersinamulti-threadedapplication?

A.Usingjava.lang.Math.random()B.Usingjava.util.concurrent.ThreadLocalRandomC.Usingjava.util.RandomAccessD.Usingjava.lang.ThreadLocal<T>

AnswerWhichoneofthefollowingoptionsisbestsuitedforgeneratingrandomnumbersinamulti-threadedapplication?

A.Usingjava.lang.Math.random()B.Usingjava.util.concurrent.ThreadLocalRandomC.Usingjava.util.RandomAccessD.Usingjava.lang.ThreadLocal<T>

Explanationb)Usingjava.util.concurrent.ThreadLocalRandom

java.lang.Math.random()isnotefficientforconcurrentprograms.UsingThreadLocalRandomresultsinlessoverheadandcontentionwhencomparedtousingRandomobjectsinconcurrentprograms(andhenceusingthisclasstypeisthebestoptioninthiscase).

java.util.RandomAccess isunrelatedtorandomnumbergeneration.

ThreadLocal<T>classprovidessupportforcreatingthread-localvariables.


QuestionConsiderthefollowingcodesegment:

while((ch =inputFile.read())!=VALUE){outputFile.write((char)ch );

}

AssumethatinputFile isoftypeFileReader ,andoutputFile isoftypeFileWriter ,andch isoftypeint .Themethodread()returnsthecharacterifsuccessful,orVALUEiftheendofthestreamhasbeenreached.WhatisthecorrectvalueofthisVALUEcheckedinthewhileloopforend-of-stream?

A.-1B.0C.255D.Integer.MAX_VALUEE.Integer.MIN_VALUE

AnswerConsiderthefollowingcodesegment:

while((ch =inputFile.read())!=VALUE){outputFile.write((char)ch );

}

AssumethatinputFile isoftypeFileReader ,andoutputFile isoftypeFileWriter ,andch isoftypeint .Themethodread()returnsthecharacterifsuccessful,orVALUEiftheendofthestreamhasbeenreached.WhatisthecorrectvalueofthisVALUEcheckedinthewhileloopforend-of-stream?

A.-1B.0C.255D.Integer.MAX_VALUEE.Integer.MIN_VALUE

ExplanationA.-1

Theread()methodreturnsthevalue-1ifend-of-stream(EOS)isreached,whichischeckedinthiswhileloop.


QuestionConsiderthefollowingprogramanddeterminetheoutput:

class Test{public void print(Integer i){

System.out.println("Integer");}public void print(int i){

System.out.println("int");}public void print(long i){

System.out.println("long");}public static void main(Stringargs[]){

Testtest =new Test();test.print(10);

}}

A.Theprogramresultsinacompilererror(“ambiguousoverload”)B.longC.IntegerD.int

AnswerConsiderthefollowingprogramanddeterminetheoutput:

class Test{public void print(Integer i){

System.out.println("Integer");}public void print(int i){

System.out.println("int");}public void print(long i){

System.out.println("long");}public static void main(Stringargs[]){

Testtest =new Test();test.print(10);

}}

A.Theprogramresultsinacompilererror(“ambiguousoverload”)B.longC.IntegerD.int

ExplanationD.int

IfIntegerandlongtypesarespecified,aliteralwillmatchtoint.So,theprogramprintsint.


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