java认证 习题 第06章 有答案版 OK该试题还有第0405章.docx
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java认证 习题 第06章 有答案版 OK该试题还有第0405章.docx
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java认证习题第06章有答案版OK该试题还有第0405章
第6章练习题
一、String、StringBuffer、StringBuilder
1(4).Given:
classTKO{
publicstaticvoidmain(String[]args){
Strings="-";
Integerx=343;
longL343=343L;
if(x.equals(L343))s+=".e1";
if(x.equals(343))s+=".e2";
Shorts1=(short)((newShort((short)343))/(newShort((short)49)));
if(s1==7)s+="=s";
if(s1 System.out.println(s); }} WhichofthefollowingwillbeincludedintheoutputStrings? (Chooseallthatapply.) A..e1 B..e2 C.=s D.fly E.Noneoftheabove. F.Compilationfails. G.Anexceptionisthrownatruntime. 2(10). aboutthethreejava.langclassesString,StringBuilder,andStringBufferaretrue? (Chooseallthatapply.) A.Allthreeclasseshavealength()method. B.ObjectsoftypeStringBufferarethread-safe. C.Allthreeclasseshaveoverloadedappend()methods. D.The"+"isanoverloadedoperatorforallthreeclasses. E.AccordingtotheAPI,StringBufferwillbefasterthanStringBuilderundermost implementations. F.Thevalueofaninstanceofanyofthesethreetypescanbemodifiedthroughvarious methodsintheAPI. 3(13)Given: classPolish{ publicstaticvoidmain(String[]args){ intx=4; StringBuffersb=newStringBuffer("..fedcba"); sb.delete(3,6); sb.insert(3,"az"); if(sb.length()>6)x=sb.indexOf("b"); sb.delete((x-3),(x-2)); System.out.println(sb); Whatistheresult? A..faza B..fzba C...azba D..fazba E...fezba F.Compilationfails. 4(22) whatStringinstancemethodwouldreturntruewheninvokedlikethis a.method(b); wherea="GROUNDhog"andb="groundHOG" selectallanswers A.equals() B.toLowercase() C.toUppercase() D.equalsIgnoreCase() E.Noneoftheabove 5(25) Attheendofthesetwolinesofcode: Strings="hypertext"; Stringt=s.subString(2,5); Whatdoestheobjectreferencetcontain? A."yper" B."ype" C."pert" D."per" E."perte" 6(26) Whichofhefollowingstatementswouldreturnfalse? ifgiventhefollowingstatements Strings=newString("Newyear"); Strings1=newString("newYear"); A.s==s1 B.s.equals(s1) C.s=s1; D.noneoftheabove 7(28) Whichwillcompileandrunwithoutexception,generatetheoutput4247 A.classExample{ publicstaticvoidmain(String[]args){ Strings="123456789"; s=(s-"123").replace(1,3,"24")-"89"; System.out.println(s); } } B.classExample{ publicstaticvoidmain(String[]args){ StringBuffers=newStringBuffer("123456789"); s.delete(0,3).replace(1,3,"24").delete(4,6) System.out.println(s); } } C.classExample{ publicstaticvoidmain(String[]args){ StringBuffers=newStringBuffer("123456789"); s.substring(3,6).delete(1,3).insert(1,"24"); System.out.println(s); } } D.classExample{ publicstaticvoidmain(String[]args){ StringBuilders=newStringBuilder("123456789"); s.substring(3,6).delete(1,2).insert(1,"24"); System.out.println(s); } } 8(29) classExample{ publicstaticvoidmain(String[]args){ Strings="ABCD"; s.concat("E"); s.replace('C','F'); System.out.println(s); } } whatwillbeprintedout? A.CompilationErrorssaystheStringisimmutable B.ABFDE C.ABCDE D.ABCD 9(33) classExample{ publicstaticvoidmain(String[]args){ Stringstr="Welcome"; str.concat("Tojava"); System.out.println(str); } } whatwillbeprintedout? A.theStringisimmutable,CompilationErrorsatline3 B.theStringisimmutable,RunExceptionatline3 C.Prints"Welcome" D.prints"WelcomeTojava" 10.(39) classExample{ publicstaticvoidmain(String[]args){ Strings1=newString("amit"); Strings2=s1.replace('m','i'); s1.concat("Poddar"); System.out.println(s1); System.out.println((s1+s2).charAt(5)); } } whatwillbeprintedout? A.CompilationError B.amitPoddaro C.amitPoddari D.amiti 二、I/O、串行化 1 (2)Given: importjava.io.*; classPlayer{ Player(){System.out.print("p");} } classCardPlayerextendsPlayerimplementsSerializable{ CardPlayer(){System.out.print("c");} publicstaticvoidmain(String[]args){ CardPlayerc1=newCardPlayer(); try{ FileOutputStreamfos=newFileOutputStream("play.txt"); ObjectOutputStreamos=newObjectOutputStream(fos); os.writeObject(c1); os.close(); FileInputStreamfis=newFileInputStream("play.txt"); ObjectInputStreamis=newObjectInputStream(fis); CardPlayerc2=(CardPlayer)is.readObject(); is.close(); }catch(Exceptionx){} } } Whatistheresult? A.pc B.pcc C.pcp D.pcpc E.Compilationfails. F.Anexceptionisthrownatruntime. 2(3) Given: bwisareferencetoavalidBufferedWriter Andthesnippet: 15.BufferedWriterb1=newBufferedWriter(newFile("f")); 16.BufferedWriterb2=newBufferedWriter(newFileWriter("f1")); 17.BufferedWriterb3=newBufferedWriter(newPrintWriter("f2")); 18.BufferedWriterb4=newBufferedWriter(newBufferedWriter(bw)); Whatistheresult? A.Compilationsucceeds. B.Compilationfailsdueonlytoanerroronline15. C.Compilationfailsdueonlytoanerroronline16. D.Compilationfailsdueonlytoanerroronline17. E.Compilationfailsdueonlytoanerroronline18. F.Compilationfailsduetoerrorsonmultiplelines. 3(6) importjava.io.*; classKeyboard{} publicclassComputerimplementsSerializable{ privateKeyboardk=newKeyboard(); publicstaticvoidmain(String[]args){ Computerc=newComputer(); c.storeIt(c); } voidstoreIt(Computerc){ try{ ObjectOutputStreamos=newObjectOutputStream( newFileOutputStream("myFile")); os.writeObject(c); os.close(); System.out.println("done"); }catch(Exceptionx){System.out.println("exc");} } } Whatistheresult? (Chooseallthatapply.) A.exc B.done C.Compilationfails. D.Exactlyoneobjectisserialized. E.Exactlytwoobjectsareserialized. 4(7) Giventhefewestfragmentspossible(andfillingthefewestslotspossible),completethecode belowsothattheclassbuildsadirectorynamed"dir3"andcreatesafilenamed"file3"inside "dir3".Noteyoucanuseeachfragmenteitherzerooronetimes. Code: importjava.io.______________ classMaker{ publicstaticvoidmain(String[]args){ _________________________________ _________________________________ _________________________________ _________________________________ _________________________________ _________________________________ _________________________________ }} Fragments: File;FileDescriptor;FileWriter;Directory; try{.createNewDir();FiledirFile {}(Exceptionx)("dir3");file file.createNewFile();=newFile=newFile dir(dir,"file3");(dir,file);.createFile(); }catch("dir3","file3");.mkdir();Filefile Answer: importjava.io.File; classMaker{ publicstaticvoidmain(String[]args){ try{ Filedir=newFile("dir3"); dir.mkdir(); Filefile=newFile(dir,"file3"); file.createNewFile(); }catch(Exceptionx){} }} 5(12) Given: importjava.io.*; classDirectories{ staticString[]dirs={"dir1","dir2"}; publicstaticvoidmain(String[]args){ for(Stringd: dirs){ //insertcode1here Filefile=newFile(path,args[0]); //insertcode2here } } } andthattheinvocation javaDirectoriesfile2.txt isissuedfromadirectorythathastwosubdirectories,"dir1"and"dir1",andthat"dir1"hasa file"file1.txt"and"dir2"hasafile"file2.txt",andtheoutputis"falsetrue",which set(s)ofcodefragmentsmustbeinserted? (Chooseallthatapply.) A.Stringpath=d; System.out.print(file.exists()+""); B.Stringpath=d; System.out.print(file.isFile()+""); C.Stringpath=File.separator+d; System.out.print(file.exists()+""); D.Stringpath=File.separator+d; System.out.print(file.isFile()+""); 6(15) Given: importjava.io.*; publicclassTestSer{ publicstaticvoidmain(String[]args){ SpecialSerials=newSpecialSerial(); try{ ObjectOutputStreamos=newObjectOutputStream( newFileOutputStream("myFile")); os.writeObject(s);os.close(); System.out.print(++s.z+""); ObjectInputStreamis=newObjectInputStream( newFileInputStream("myFile")); SpecialSerials2=(SpecialSerial)is.readObject(); is.close(); System.out.println(s2.y+""+s2.z); }catch(Exceptionx){System.out.println("exc");} classSpecialSerialimplementsSerializable{ transientinty=7; staticintz=9; Whicharetrue? (Chooseallthatapply.) A.Compilationfails. B.Theoutputis1009 C.Theoutputis10010 D.Theoutputis1079 E.Theoutputis10710 F.InordertoalterthestandarddeserializationprocessyouwouldoverridethereadObject() methodinSpecialSerial. G.Inordertoalterthestandarddeserializationprocessyouwouldoverridethe defaultReadObject()methodinSpecialSerial. 7(3)Whatisresultwhenyoucompileandrunthefollowingcode? importjava.io.*; publicclassExample {publicstaticvoidmain(String[]args){ Filef=newFile("hello.test"); try{ FileOutputStreamout=newFileOutputStream(f); } catch(FileNotFoundExceptione){} } } A.Createanewfilenamed"hello.test"ifitdoesnotyetexit.Italsoopensthefilesoyoucanwritetoitandreadfromit B.Createanewfilenamed"hello.test"ifitdoesnotyetexit.Thefileisnotopened C.openafilenamed"hello.test"sothatyoucanwritetoitandreadfromit,butdoesnotcreatethefileifitdoesnotyetexit D.openafilenamed"hello.test"sothatyoucanwritetoitbutcannotreadfromit 8(4)Whatisresultwhenyoucompileandrunthefollowingcode? importjava.io.*; publicclassExample {publicstaticvoidmain(String[]args){ Filef=newFile("c: \\large.txt"
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