JAVA基础面试题2答案版

1、JAVA语言基础笔试题-2Question1Given:classApublicvoidprocess()System.out.print(“A)“classBextendsApublicvoidprocess()throwsRuntimeExceptioncess();if(true)thrownewRuntimeException();System.out.print(“B)”publicstaticvoidmain(Stringargs)try(A)newB().process();catch(Exceptione)System.out.print(“Exception)“Whatist

2、heresult?ExceptionAExceptionAExceptionBABExceptionCompilationfailsbecauseofanerrorinline14.Compilationfailsbecauseofanerrorinline19.答案：B考点：方法的重写(重写方法异常抛出部分的理解)多态异常处理说明：子类重写父类方法，不能抛出比父类方法更多的异常，但此处子类重写方法声明抛出了RuntimeException,不算多抛，算是平抛，是可以的。RuntimeException是Exception的子类，可以被Exception捕获。Question2Given:st

3、aticclassAvoidprocess()throwsExceptionthrownewException();TOC o 1-5 h zstaticclassBextendsAvoidprocess()System.out.println(“B)”publicstaticvoidmain(Stringargs)18.Aa=newB();cess();Whatistheresult?BThecoderunswithnooutput.Anexceptionisthrownatruntime.Compilationfailsbecauseofanerrorinline15.Compilatio

4、nfailsbecauseofanerrorinline18.Compilationfailsbecauseofanerrorinline19.答案：F考点：方法的重写(重写方法异常抛出部分的理解)多态静态内部类以及其实例的创建说明：19.cess();是多态调用，调用的应该是类B的process方法，这个方法只是允许抛出RuntimeException,所以19行在理论上不需要进行异常相关处理，系统会自动抛出该异常，但是多态只是在运行时，系统方能识别，在编译的时候，系统还是按照类A的process方法来进行验证，所以出现错误，因为类A抛出的是检查异常，必须显式被捕获或者抛出。Question

5、3Given:staticclassAvoidprocess()throwsExceptionthrownewException();TOC o 1-5 h zstaticclassBextendsAvoidprocess()System.out.println(“B”);publicstaticvoidmain(Stringargs)newB().process();Whatistheresult?BThecoderunswithnooutput.Compilationfailsbecauseofanerrorinline12.Compilationfailsbecauseofanerror

6、inline15.Compilationfailsbecauseofanerrorinline18.答案：A考点：方法的重写(重写方法异常抛出部分的理解)静态内部类以及其实例的创建Question4Given:tryResourceConnectioncon=resourceFactory.getConnection();Resultsr=con.query(“GETINFOFROMCUSTOM)ER”info=r.getData();con.close();catch(ResourceExceptionre)errorLog.write(re.getMessage();returninfo;

7、WhichistrueifaResourceExceptionisthrownonline86?Line92willnotexecute.Theconnectionwillnotberetrievedinline85.Theresourceconnectionwillnotbeclosedonline88.Theenclosingmethodwillthrowanexceptiontoitscaller.答案：C考点：try.catch结构的理解异常的捕获和处理说明：由于抛出的ResourceException,能够被catch块捕获（标配），所以异常在方法中就被处理掉了，不会抛出该方法。根据

8、try块操作上规定，一旦抛出异常，抛出异常语句后续部分的try块语句将不再运行。Question5ClicktheExhibitbutton.publicclassApublicvoidmethod1()Bb=newB();b.method2();/morecodeherepublicclassBpublicvoidmethod2()Cc=newC();c.method3();5./morecodehere6.7.publicclassCpublicvoidmethod3()/morecodehereGiven:tryAa=newA();a.method1();catch(Exceptione

9、)System.out.print(“anerroroccurred!)”WhichtwoaretrueifaNullPointerExceptionisthrownonline3ofclassC?(Choosetwo.)Theapplicationwillcrash.Thecodeonline29willbeexecuted.Thecodeonline5ofclassAwillexecute.Thecodeonline5ofclassBwillexecute.Theexceptionwillbepropagatedbacktoline27.答案：BE考点：异常的抛出、捕获和处理说明：一般来说

10、，异常的抛出，最终终将被处理，本方法不处理，则抛给主调方法，关键是要能抛的出去，因为NullpointerException是RuntimeException,所以一路没有阻碍，最终propagatedback到达27行，Exception是所有异常的父类，所以该异常在这里被处理了,Question6ClicktheExhibitbutton.publicclassApublicvoidmethod1()tryBb=newB();b.method2();/morecodeherecatch(TestExceptionte)thrownewRuntimeException(te);publicc

11、lassBpublicvoidmethod2()throwsTestException/morecodeherepublicclassTestExceptionextendsExceptionGiven:publicvoidmethod()Aa=newA();a.method1();WhichistrueifaTestExceptionisthrownonline3ofclassB?Line33mustbecalledwithinatryblock.Theexceptionthrownbymethod1inclassAisnotrequiredtobecaught.Themethoddecla

12、redonline31mustbedeclaredtothrowaRuntimeException.Online5ofclassA,thecalltomethod2ofclassBdoesnotneedtobeplacedinatry/catchblock.答案：B考点：异常抛出、捕获和处理说明：第8行，把检查异常TestException封装在RuntimeException中抛出是可以，因为系统仍然认为你抛出的是一个运行时异常，任何方法都默认支持抛出运行时异常。Question7Given:publicstaticvoidmain(Stringargs)tryargs=null;args0

13、=”test;”System.out.println(args0);catch(Exceptionex)System.out.println(“Exception)”catch(NullPointerExceptionnpe)System.out.println(“NullPointerException”)Whatistheresult?testExceptionCompilationfails.NullPointerException答案：C考点：异常的捕获处理说明：Exception是能够捕获所有异常的万金油，其一般放在捕获块的最后一环，用来捕获所有的漏网之鱼，如果放在捕获块最前头，将导

14、致后头的捕获块永远无法得到运行，最后产生编译失败。Question8Given:staticvoidtest()throwsErrorif(true)thrownewAssertionError();System.out.print(“test“)publicstaticvoidmain(Stringargs)trytest();catch(Exceptionex)System.out.print(“exception)“;System.out.print(“end”)Whatistheresult?endCompilationfails.exceptionendexceptiontesten

15、dAThrowableisthrownbymain.AnExceptionisthrownbymain.答案：E考点：Error和Exception的关系的理解说明：Error和Exception是兄弟类，其有一个共同的父类Throwable,所以Error也可以被抛出。Exception捕获块无法捕获Error,所以这里Error会被抛出，由JVM做了最终处理。Question9Given:staticvoidtest()tryStringx=null;System.out.print(x.toString()+”);TOC o 1-5 h zfinallySystem.out.print(

16、“finally)”;publicstaticvoidmain(Stringargs)trytest();catch(Exceptionex)System.out.print(“exception”);Whatistheresult?nullfinallynullfinallyCompilationfails.finallyexception答案：E考点：try.catch.finally结构理解说明：允许存在try.finally结构，即使没有catch块的存在。这里try块会产生一个经典的异常NullPointerException,其是RuntimeException,可以被默认抛出，但

17、抛出之前，需要执行一次finally.Question10Given:staticvoidtest()throwsRuntimeExceptiontrySystem.out.print(“test)”thrownewRuntimeException();catch(Exceptionex)System.out.print(“exception”);publicstaticvoidmain(Stringargs)trytest();catch(RuntimeExceptionex)System.out.print(“urntime”);System.out.print(“end)”Whatist

18、heresult?testendCompilationfails.testruntimeendtestexceptionendAThrowableisthrownbymainatruntime.答案：D考点：异常的抛出、捕获和处理说明：本题test方法已经在内部把异常处理，该异常没有被抛给main方法。Question11Givenamethodthatmustensuethatitsparameterisnotnull:publicvoidsomeMethod(Objectvalue)/checkfornullvalueSystem.out.println(value.getClass();

19、What,insertedatline12,istheappropriatewaytohandleanullvalue?assertvalue=null;assertvaluenull,valueisnull!if(value=null)thrownewAssertionException(“valueisnull!)”if(value=null)thrownewIllegalArgumentException(“valueisnull)”答案：D考点：常见异常类的使用Question12ClicktheExhibitbutton.publicclassClassApublicvoidmeth

20、odA()ClassBclassB=newClassB();classB.getValue();And:classClassBpublicClassCclassC;22.publicStringgetValue()returnclassC.getValue();And:classClassCpublicStringvalue;32.publicStringgetValue()value=“ClassB”;returnvalue;Given:ClassAa=newClassA();a.methodA();Whatistheresult?Compilationfails.ClassCisdispl

21、ayed.Thecoderunswithnooutput.Anexceptionisthrownatruntime.答案：D考点：常见异常的识别(NullpinterException)说明：第24行，对classC的getValue方法调用，由于classC的实例不存在，所以无法运行。抛出异常，这种情况只有在运行的时候才知道，不会认为是编译错误。Question13Given:publicclassFoostaticinta;statica0=2;publicstaticvoidmain(Stringargs)Whichexceptionorerrorwillbethrownwhenapro

22、grammerattemptstorunthiscode?java.lang.StackOverflowErrorjava.lang.IllegalStateExceptionjava.lang.ExceptionlnlnitializerErrorjava.lang.ArraylndexOutOfBoundsException答案：C考点：静态块以及常见异常的识别说明：在静态块中，对a进行了调用，但a没有指向任何对象，所以抛出NullpinterException,但由于是发生在静态块中，所以系统最终抛出了ExceptionlnlnitializerErrorQuestion14Given:

23、publicclassClassApublicvoidcount(inti)count(+i);And:ClassAa=newClassA();a.count(3);Whichexceptionorerrorshouldbethrownbythevirtualmachine?StackOverflowErrorNullPointerExceptionNumberFormatExceptionIllegalArgumentExceptionExceptionlnlnitializerError答案：A考点：递归调用理解、堆栈的运作模式说明：此处count方法产生无穷递归调用，最终导致堆栈空间溢出

24、。Question15Given:publicclassBoxer1Integeri;intx;publicBoxer1(inty)x=i+y;System.out.println(x);publicstaticvoidmain(Stringargs)newBoxer1(newInteger(4);Whatistheresult?Thevalue4isprintedatthecommandlineCompilationfailsbecauseofanerrorinline5.Compilationfailsbecauseofanerrorinline9.ANullPointerExceptio

25、noccursatruntime.ANumberFormatExceptionoccursatruntime.AnIllegalStateExceptionoccursatruntime.答案：D考点：自动装箱和拆箱、基本类型和类类型说明：x=i+y,i是类类型为null,这里其实系统是采取一个自动拆箱操作，也就是对value();所以此处抛出一个NullpinterExceptionQuestion16Given:publicclassTestString1publicstaticvoidmain(Stringargs)Stringstr=”420”str+=42;System.out.pr

26、int(str);答案：D考点：字符串概念的理解说明：字符串和任何基本类型相加，最终其将全部转成字符串“420”+42-“420”+newInteger(42).toString();Whatistheoutput?4242046242042Compilationfails.Anexceptionisthrownatruntime.Question17Given:classConverterpublicstaticvoidmain(Stringargs)Integeri=args0;intj=12;System.out.println(“Itis”+(j=i)+“thatj=i”);Whati

27、stheresultwhentheprogrammerattemptstocompilethecodeandrunitwiththecommandjavaConverter12?Itistruethatj=i.Itisfalsethatj=i.Anexceptionisthrownatruntime.Compilationfailsbecauseofanerrorinline13.答案：D考点：命令行参数理解说明：任何的命令行参数，都将被理解为字符串，即使是数字参数也是如此，需要做转换，比女叮ntegeri=Integer.parselnt(argsO);Question18Giventhis

28、methodinaclass:publicStringtoString()StringBufferbuffer=newStringBuffer();buffer.append(“”)returnbuffer.toString();Whichistrue?ThiscodeisNOTthread-safe.TheprogrammercanreplaceStringBufferwithStringBuilderwithnootherchanges.ThiscodewillperformwellandconvertingthecodetouseStringBuilderwillnotenhanceth

29、eperformance.Thiscodewillperformpoorly.Forbetterperformance,thecodeshouldberewritten:return“”答案：B考点：StringBuffer和StringBuilder的理解说明：StringBuffer是线程安全的，速度较慢；StringBuilder是线程不安全的，速度较快。两者API一致，主要是为了克服字符串不变性的特性而存在。Question19Given:publicclassMyLoggerprivateStringBuilderlogger=newStringBuilder();publicvoi

30、dlog(Stringmessage,Stringuser)logger.append(message);logger.append(user);TheprogrammermustguaranteethatasingleMyLoggerobjectworksproperlyforamulti-threadedsystem.Howmustthiscodebechangedtobethread-safe?synchronizethelogmethodreplaceStringBuilderwithStringBufferNochangeisnecessary,thecurrentMyLoggerc

31、odeisalreadythread-safe.replaceStringBuilderwithjustaStringobjectandusethestringconcatenation(+=)withinthelogmethod答案：B考点：StringBuffer和StringBuilder的理解Question20Given:publicStringmakinStrings()Strings=“Fred”s=s+“47”s=s.substring(2,5);s=s.toUpperCase();returns.toString();HowmanyStringobjectswillbecre

32、atedwhenthismethodisinvoked?123456答案：E考点：字符串不变性说明：任何字符串的运算结果都将产生一个新的字符串对象。Question21publicclassTestString3publicstaticvoidmain(Stringargs)/insertcodehereSystem.out.println(s);Whichtwocodefragments,insertedindependentlyatline3,generatetheoutput4247?(Choosetwo.)Strings=“123456789”;s=(s-”123”).replace(

33、1,3,”24-”“)89”;StringBuffers=newStringBuffer(”123456789”);s.delete(0,3).replace(1,3,“24”).delete(4,6);StringBuffers=newStringBuffer(”123456789”);s.substring(3,6).delete(1,3).insert(1,“24”);StringBuilders=newStringBuilder(”123456789”);s.substring(3,6).delete(1,2).insert(1,“24”);StringBuilders=newStri

34、ngBuilder(”123456789”);s.delete(0,3).delete(1,3).delete(2,5).insert(1,“24”);答案：BE考点：StringBufferAPI的使用说明：s.delete(0,3)或者s.subString(0,3)以上均为从0位开始操作，不包含3位。Question22Given:publicclassYikes12.publicstaticvoidgo(Longn)System.out.println(“Long“);publicstaticvoidgo(Shortn)System.out.println(“Short“);publi

35、cstaticvoidgo(intn)System.out.println(“int“);publicstaticvoidmain(Stringargs)shorty=6;longz=7;go(y);go(z);Whatistheresult?intLongShortLongCompilationfails.Anexceptionisthrownatruntime.答案：A考点：重载以及不匹配参数的撮合识别说明：如果基本类型没有对应的方法参数，则往更高精度升级，如果有找到匹配的，则执行。如果基本类型即使升级也无法找到合适的，则进行装箱，升级为类类型，然后寻求匹配，如过能匹配，则成功，不能匹配，

36、则编译失败，在类类型，不会再寻求向上升级。Question23Given:publicclassWowpublicstaticvoidgo(shortn)System.out.println(“short”);publicstaticvoidgo(Shortn)System.out.println(“SHORT)”;publicstaticvoidgo(Longn)System.out.println(“LONG)”;publicstaticvoidmain(Stringargs)Shorty=6;intz=7;go(y);go(z);Whatistheresult?shortLONGSHOR

37、TLONGCompilationfails.Anexceptionisthrownatruntime.答案：C考点：重载以及不匹配参数的撮合识别说明：基本类型可以尝试升级，但如果即使升级也无法匹配的话，就会装箱成为类对象去尝试匹配，匹配失败，则失败，不会去在类层面进行类型升级。类型升级只有在基本类型是可以进行的，自动升级的方向都是从低精度向高精度自动升级。Question24Given:classMakeFilepublicstaticvoidmain(Stringargs)tryFiledirectory=newFile(“d)”;Filefile=newFile(directory,”f)”;if(!file.exists()file.createNewFile();catch(IOExceptione)e.printStackTrace();ThecurrentdirectorydoesNOTcontainadirectorynamedd.Whichthreearetr