OCP Java SE 8 Exam Sample Questions

LambdaExpressions

HariKiran&SGGanesh

Ques8onWhichofthesearevalidlambdaexpressions(selectALLthatapply):

A.(intx)->x+xB.x->x%xC.->7D.(arg1,intarg2)->arg1/arg2

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AnswerWhichofthesearevalidlambdaexpressions(selectALLthatapply):

A.(intx)->x+xB.x->x%xC.->7D.(arg1,intarg2)->arg1/arg2

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Explana8onA.&B.arecorrectlambdaexpressions.Whyotherop8onsarewrong:C.->7.ifnoparameters,thenemptyparenthesis()mustbeprovidedi.e.,()->7D.(arg1,intarg2)->arg1/arg2ifargumenttypesareprovided,thenitshouldbeprovidedforallthearguments,ornoneofthem

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Ques8onDeterminethebehaviourofthefollowingprogram:class BlockLambda { interface LambdaFunction {

String intKind(int a); } public static void main(String []args) {

LambdaFunction lambdaFunction = (int i) -> { //#1 if((i % 2) == 0) return "even";

else return "odd"; }; System.out.println(lambdaFunction.intKind(10)); } }

A.Compilererrorat#1B.PrintsevenC.PrintsoddD.RunKmeerror(throwsexcepKon)

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AnswerDeterminethebehaviourofthefollowingprogram:class BlockLambda { interface LambdaFunction {

String intKind(int a); } public static void main(String []args) {

LambdaFunction lambdaFunction = (int i) -> { //#1 if((i % 2) == 0) return "even";

else return "odd"; }; System.out.println(lambdaFunction.intKind(10)); } }

A.Compilererrorat#1B.PrintsevenC.PrintsoddD.RunKmeerror(throwsexcepKon)

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Explana8onB.isthecorrectanswerastheexpressionevaluatesinputvalueasevenWhyotherop8onsarewrong:A.ThereisnocompilaKonerror,thisiscorrectwayofdefiningblocklambdaC.Inputvaluepassedis10sotheexpressionreturnsevenD.Thisprogramdoesn’tthrownanyrunKmeexcepKons

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Ques8onPredicttheoutputofbelowprogram:

interface SuffixFunction { void call(); } class Latin { public static void main(String []args) { String word = "hello"; SuffixFunction suffixFunc = () -> System.out.println(word + "ay"); word = "e"; suffixFunc.call(); } } Choosethecorrectop8on A.PrintshelloayB.PrintshelloeC.PrintseayD.Compilererror

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AnswerPredicttheoutputofbelowprogram:

interface SuffixFunction { void call(); } class Latin { public static void main(String []args) { String word = "hello"; SuffixFunction suffixFunc = () -> System.out.println(word + "ay"); word = "e"; suffixFunc.call(); } } Choosethecorrectop8on A.PrintshelloayB.PrintshelloeC.PrintseayD.CompilererrorLaKn.java:7:error:localvariablesreferencedfromalambdaexpressionmustbefinaloreffecKvelyfinal

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Explana8onInsidethelambdaexpression,weareusingthelocalvariableword.Becauseitisusedinalambdaexpression,thisvariableisconsideredtobefinal(thoughitisnotexplicitlydeclaredfinal).HenceA,BandCareincorrectopKonsSnippet String word = "hello"; SuffixFunction suffixFunc = () -> System.out.println(word + "ay"); word = "e";

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Ques8onWhichofthefollowinghascorrectusageoffunc8onalinterfacesanddoesn’tresultincompila8onerror(selectallthatapply):

A. @FunctionalInterface public abstract class AnnotationTest { abstract int foo(); } B. @FunctionalInterface public interface AnnotationTest { default int foo() {}; } C. @FunctionalInterface public interface AnnotationTest { /* no methods provided */ } D. @FunctionalInterface public interface Comparator<T> { int compare(T o1, T o2); boolean equals(Object obj); }

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AnswerWhichofthefollowinghascorrectusageoffunc8onalinterfacesanddoesn’tresultincompila8onerror(selectallthatapply):

A. @FunctionalInterface public abstract class AnnotationTest { abstract int foo(); } B. @FunctionalInterface public interface AnnotationTest { default int foo() {}; } C. @FunctionalInterface public interface AnnotationTest { /* no methods provided */ } D. @FunctionalInterface public interface Comparator<T> { int compare(T o1, T o2); boolean equals(Object obj); }

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Explana8onD.ThisinterfaceisafuncKonalinterfacethoughitdeclarestwoabstractmethods:compare()andequals()methods.HowisitafuncKonalinterfacewhenithastwoabstractmethods?Becauseequals()methodsignaturematchesfromObject,andthecompare()methodistheonlyremainingabstractmethod,andhencetheComparatorinterfaceisafuncKonalinterface.Whyotherop8onsarewrong:A.AnabstractclasscannotbedeclaredwithannotaKon@FuncKonalInterfaceC.andB.doesn’thaveabstractmethods.HencetheydonoqualifytobedeclaredasfuncKonalinterfaces

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Ques8onPredicttheoutputofbelowprogram:

class LambdaFunctionTest { @FunctionalInterface interface LambdaFunction {

int apply(int j); boolean equals(java.lang.Object arg0);

} public static void main(String []args) {

LambdaFunction lambdaFunction = i -> i * i; // #1 System.out.println(lambdaFunction.apply(10));

} }

A.Thisprogramresultsinacompilererror:interfacescannotbedefinedinsideclassesB.Thisprogramresultsinacompilererror:@FuncKonalInterfaceusedforLambdaFuncKonthatdefinestwoabstractmethodsC.Thisprogramresultsinacompilererrorincodemarkedwith#1:syntaxerrorD.Thisprogramcompileswithouterrors,andwhenrun,itprints100inconsole

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AnswerPredicttheoutputofbelowprogram:

class LambdaFunctionTest { @FunctionalInterface interface LambdaFunction {

int apply(int j); boolean equals(java.lang.Object arg0);

} public static void main(String []args) {

LambdaFunction lambdaFunction = i -> i * i; // #1 System.out.println(lambdaFunction.apply(10));

} }

A.Thisprogramresultsinacompilererror:interfacescannotbedefinedinsideclassesB.Thisprogramresultsinacompilererror:@FuncKonalInterfaceusedforLambdaFuncKonthatdefinestwoabstractmethodsC.Thisprogramresultsinacompilererrorincodemarkedwith#1:syntaxerrorD.Thisprogramcompileswithouterrors,andwhenrun,itprints100inconsole

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Explana8onD.isthecorrectanswerasthisprogramcompileswithouterrors,andwhenrun,itprints100inconsole.

Whyotherop8onsarewrong:

A.  Aninterfacecanbedefinedinsideaclass

B.  ThesignatureoftheequalsmethodmatchesthatoftheequalmethodinObjectclass;henceitisnotcountedasanabstractmethodinthefuncKonalinterface

C.  ItisacceptabletoomittheparametertypewhenthereisonlyoneparameterandtheparameterandreturntypeareinferredfromtheLambdaFuncKonabstractmethoddeclaraKonintapply(intj)

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Ques8onPredicttheoutputofbelowprogram:

interface DoNothing { default void doNothing() { System.out.println("doNothing"); } } @FunctionalInterface interface DontDoAnything extends DoNothing { @Override abstract void doNothing(); } class LambdaTest { public static void main(String []args) {

DontDoAnything beIdle = () -> System.out.println("be idle"); beIdle.doNothing();

} } A.ThisprogramresultsinacompilererrorforDontDoAnythinginterface:cannotoverridedefaultmethodtobeanabstractmethodB.Thisprogramprints:beidleC.Thisprogramprints:doNothingD.Thisprogramresultsinacompilererror:DontDoAnythingisnotafuncKonalinterface

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AnswerPredicttheoutputofbelowprogram:

interface DoNothing { default void doNothing() { System.out.println("doNothing"); } } @FunctionalInterface interface DontDoAnything extends DoNothing { @Override abstract void doNothing(); } class LambdaTest { public static void main(String []args) {

DontDoAnything beIdle = () -> System.out.println("be idle"); beIdle.doNothing();

} } A.ThisprogramresultsinacompilererrorforDontDoAnythinginterface:cannotoverridedefaultmethodtobeanabstractmethodB.Thisprogramprints:beidleC.Thisprogramprints:doNothingD.Thisprogramresultsinacompilererror:DontDoAnythingisnotafuncKonalinterface

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Explana8onB.isthecorrectanswerasthecallbeIdle.doNothing()callstheSystem.out.printlngiveninthelambdaexpressionandhenceitprints“beidle”ontheconsoleWhyotherop8onsarewrong:A.  Adefaultmethodcanbeoverriddeninaderivedinterface

andcanbemadeabstractC.DoNothing.doNothing()willnotbecalledD.DontDoNothingisafuncKonalinterfacebecauseithasanabstractmethod

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