Java語言程序設(shè)計(jì)課后習(xí)題答案英文版

Chapter2PrimitiveDataTypesandOperations

1.

Valididentifiers:applet,Applet,$4,appslnvalididentifiers:a++,-a,4#R,#44

2.

Keywords:

class,public,int

3.

doublemiles=100;

finaldoubleMILE_TO_KILOMETER=1.609;

doublekilometer=MILE_TO_KILOMETER*miles;

System.out.println(kilometer);

Thevalueofkilometeris160.9.

4.Therearethreebenefitsofusingconstants:(l)youdon'thavetorepeatedlytypethesame

value;(2)thevaluecanbechangedinasinglelocation,ifnecessary;(3)theprogramiseasyto

read,finalintSIZE=20;

5.

a=46/9;=>a=5

a=46%9+4*4-2;=>a=l+16-2=15

a=45+43%5*(23*3%2);=>a=45+3*(1)=48

a%=3/a+3;=>a%=3+3;a%=6=>a=a%6=l;

d=4+d*d+4;=>4+1.0+4=9.0

d+=1.5*3+(++a);=>d+=4.5+2;d+=6.5;=>d=7.5

d-=1.5*3+a++;=>d-=4.5+1；=>d=1-5.5=-4.5

6.

2

2

-4

-4

0

1

7.

Forbyte,from-128to127,inclusive.

Forshort,from-32768to32767,inclusive.

Forint,from-2147483648to2147483647,inclusive.

Forlong,from-9223372036854775808to9223372036854775807.

Forfloat,thesmallestpositivefloatisl.40129846432481707e-45andthelargestfloat

js3.40282346638528860e+38.

Fordouble,thesmallestpositivedoubleis4.94065645841246544e-324andthelargestdouble

isl.79769313486231570e+308d.

8.

25/4=6.Ifyouwantthequotienttobeafloating-point

number,rewriteitas25.0/4.0.

9.

Yes,thestatementsarecorrect.Theprintoutis

theoutputfor25/4is6;

theoutputfor25/4.0is6.25;

10.4.0/(3.0*(r+34))-9*(a+b*c)+(3.0+d*

(2+a))/(a+b*d)

11.bandcaretrue.

12.

All.

13.

Line2:Missingstaticforthemainmethod.

Line2:stringshouldbeString.

Line3:iisdefinedbutnotinitializedbeforeitis

usedinLine5.

Line4:kisanint,cannotassignadoublevaluetok.

Lines7-8:Thestringcannotbebrokenintotwolines.

14.

Yes.Differenttypesofnumericvaluescanbeusedinthesamecomputationthroughnumeric

conversionsreferredtoascasting.

15.Thefractionalpartistruncated.Castingdoesnotchangethevariablebeingcast.

16.

fis12.5

iis12

17.

System.out.println((int)'l');

System.out.println((int)'A*);

System.out.println((int)'B');

System.out.println((int)'a');

System.out.println((int)'b,);

System.out.println((char)40);

System.out.println((char)59);

System.out.println((char)79);

System.out.println((char)85);

System.out.println((char)90);

System.out.println((char)0X40);

System.out.println((char)0X5A);

System.out.println((char)0X71);

System.out.println((char)0X72);

System.out.println((char)0X7A);

18.'\u345dE'iswrong.Itmusthaveexactlyfourhexnumbers.

19.'\\'and'V

20.

ibecomes49,sincetheASCIIcodeof'1'is49;

jbecome99since(int)'l'is49and(int)*2'is50;

kbecomes97sincetheASCIIcodeof'a'is97;

cbecomescharacter'z'since(int)*z'is90;

21.

charc='A';

i=(int)c;//ibecomes65

booleanb=true;

i=(int)b;//Notallowed

floatf=1000.34f;

inti=(int)f;//ibecomes1000

doubled=1000.34;

inti=(int)d;//ibecomes1000

inti=97;

charc=(char)i;//cbecomes'a'

22.

System.out.println("l"+1);=>11

System.out.println('l'+1);=>50(sincetheUnicodefor1is49

System.out.printlnCl"+1+1);=>111

System.out.println("l"+(1+1));=>12

System.out.println('l'+1+1);=>51

23.

1+"Welcome"+1+1islWelcome11.

1+"Welcome"+(1+1)islWelcome2.

1+"Welcome"+('\u0001'+1)islWelcome2

1+"Welcome"+*a'+1islWelcomeal

24.

UseDouble.parseDouble(string)toconvertadecimalstringintoadoublevalue.

UseInteger.parselnt(string)toconvertanintegerstringintoanintvalue.

25.

longtotalMills=System.currentTimeMillis()returnsthe

millisecondssinceJan1,1970.totalMills%(1000*60

*60)returnsthecurrentminute.

26.

Use//todenoteacommentline,anduse/*paragraph*/todenoteacommentparagraph.

27.

Classnames:Capitalizethefirstletterineachname.

Variablesandmethodnames:Lowercasethefirstword,

capitalizethefirstletterinallsubsequentwords.

Constants:Capitalizeallletters.

28.

publicclassTest{

/**Mainmethod*/

publicstaticvoidmain(String[]args){

//PrintalineSystem.out.println("2%3="+2%3);

29.

Compilationerrorsaredetectedbycompilers.Runtimeerrorsoccurduringexecutionofthe

program.Logicerrorsresultsinincorrectresults.

Chapter3SelectionStatements

1.<,<=,==,!=,>,>=

2.

(true)&&(3>4)false

!(x>0)&&(x>0)false

(x>0)||(x<0)true

(x!=0)11(x==0)true

(x>=0)11(x<0)true

(x!=1)==!(x==1)true

3.(x>1)&&(x<100)

4.((x>1)&&(x<100))||(x<0)

5.

x>y>0incorrect

x=y&&yincorrect

x/=ycorrect

xoryincorrect

xandyincorrect

6.No.Booleanvaluescannotbecasttoothertypes.

7.xis2.

8.xis1.

9.ddfalse-4

10.Note:elsematchesthefirstifclause.Nooutputifx=3andy=2.Output

is"zis7"ififx=3andy=4.Outputis"xis2"ififx=2andy=2.

11.a,c,anddarethesame.(B)and(C)arecorrectlyindented.

12.Nooutputifx=2andy=3.Outputis"xis3"ifx=2andy=2.

Outputis"zis6".

x>2

falsetrue

System.out.println("xis"+x);

V>2

false

true

intz=x+y;

System.out.println("zis"+z);

13.Yes.

14.0.5,0.0,0.234

15.

(int)(Math.random()*20)

10+(int)(Math.random()*10)

10+(int)(Math.random()*41)

x+=34;breakais4

ais1

x+=5;breakx+=10;breakais2

x+=16;breakais3

16.Switchvariablesmustbeofchar,byte,short,orintdatatypes.Ifabreakstatementisnot

used,thenextcasestatementisperformed.Youcanalwaysconvertaswitchstatementtoan

equivalentifstatement,butnotanifstatementtoaswitchstatement.Theuseoftheswitch

statementcanimprovereadabilityoftheprograminsomecases.Thecompiledcodeforthe

switchstatementisalsomoreefficientthanitscorrespondingifstatement.

17.yis2.

18.

switch(a){

case1:x+=5;break;

case2:x+=10;break;

case3:x+=16;break;

case4:x+=34;

}

19.System.out.print((count%10==0)?count+"\n":count+"");

20.

Thespecifiersforoutputtingabooleanvalue,acharacter,adecimalinteger;afloating-point

number,andastringare%b,%c,%d,%f,and%s.

21.

(a)thelastitem3doesnothaveanyspecifier.

(b)Thereisnotenoughitems

(c)Thedatafor%fmustafloating-pointvalue

22.

(a)amountis32.3200003.233000e+01

(b)amountis32.32003.2330e+01

(c)*false〃*denoteaspace

(d)**Java//*denoteaspace

(e)false*****Java

(f)*falseJava

23.UsetheString.formatmethodtocreateaformattedstring.

24.

Theprecedenceorderforbooleanoperatorsis&,八，|,&&,and11

true|true&&falseisfalse

true11true&&falseistrue

true|true&falseistrue.

25.

a.Theoperandsareevaluatedfirstandfromlefttoright.So(-i+i+i++)is-1-1-1.i++return

thevalueofi,theniisincrementedby1.So,inthenextprintinstatementi+++iis0+1.

b.Theoperandsareevaluatedfirstandfromlefttoright.So,theleftibeforethe+operatoris0

andrightiisassignedto1by(i=1).Thereforetheprintinstatementprints1.

c.Theoperandsareevaluatedfirstandfromlefttoright.So,beforeiintherightofthe+

operatorisevaluated,iisassignedto1.Therefore,(i=1)+ievaluatesto2.

26.

a=(a=3)+a;=>a=3+3=6

a=a+(a=3);=>a=l+3=4

a+=a+(a=3);=>thevalueofaintheleftsideof+=isobtained(1),a+(a=3)is

4,therefore,thefinalresultais5.

a=5+5*2%a—;=>a=5+10%a-=5+0=5

a=4+l+4*5%(++a+l)=>a=5+4*5%(++a+1)=5+20%(++a+1)=5+20%

(2+l)=5+20%3=5+2=7;

d+=1.5*3+(++d);=>thevalueofdintheleftsideof+=isobtained(1.0),1.5*3

+(++d)=4.5+(++d)=4.5+2.0=6.5,therefore,thefinalresultais7.5.

d-=1.5*3+d++；=>thevalueofdintheleftsideof+=isobtained(1.0),1.5*3+

d++=4.5+d++=4.5+1.0=5.5,therefore,thefinalresultis1.0-5.5=-4.5.

Chapter4Loops

1.

(A)Theloopbodyisnotexecuted.

(B)Theloopbodyisexecutedninetimes.Theprintoutis2,4,6,8on

separatelines.

2.Thedifferencebetweenado-whileloopandawhileloopistheorderofevaluatingthe

continuation-conditionandexecutingtheloopbody.Inawhileloop,thecontinuation-condition

ischeckedandthen,iftrue,theloopbodyisexecuted.Inado-whileloop,theloopbodyis

executedforthefirsttimebeforethecontinuation-conditionisevaluated.

3.Same.Whenthei++and++iareusedinisolation,theireffectsaresame.

4.

Thethreepartsinaforloopcontrolareasfollows:

Thefirstpartinitializesthecontrolvariable.

ThesecondpartisaBooleanexpressionthatdetermineswhethertheloopwill

repeat.

Thethirdpartistheadjustmentstatement,whichadjuststhecontrolvariable.

for(inti=l,i<=100,i++)

System.out.println(i);

5.Theloopkeepsdoingsomethingindefinitely.

6.No.Thescopeofthevariableisinsidetheloop.

7.Yes.Theadvantagesofforloopsaresimplicityandreadability.Compilerscanproducemore

efficientcodefortheforloopthanforthecorrespondingwhileloop.

8.

whileloop:

longsum=0;

inti=0;

while(i<=1000){

sum+=i++;

}

do-whileloop:

longsum=0;

inti=0;

do{

sum+=i++;

)

while(i<=1000);

9.No.Trynl=3andn2=3.

10.

Thekeywordbreakisusedtoexitthecurrentloop.Theprogramin(A)willterminate.Theoutput

isBalanceis1.Thekeywordcontinuecausestherestoftheloopbodytobeskippedforthe

currentiteration.Thewhileloopwillnotterminatein(B).

11.Yes.

for(inti=l;sum<10000;i++)

sum=sum+i;

12.Ifacontinuestatementisexecutedinsideaforloop,therestoftheiterationisskipped,then

theaction-after-each-iterationisperformedandtheloop-continuation-conditionischecked.Ifa

continuestatementisexecutedinsideawhileloop,therestoftheiterationisskipped,thenthe

loop-continuation-conditionischecked.

Hereisthefix:

inti=0;

while(i<4){

if(i%3==0){

i++;

continue;

)

sum+=i；

i++；

)

13.

classTestBreak{

publicstaticvoidmain(string[]args){

intsum=0;

intnumber=0;

do{

number++；

sum+=number;

}

while(number<2011sum>=100);

System.out.println("Thesumis"+sum);

classTestContinue{

publicstaticvoidmain(String[]args){

intsum=0;

intnumber=0;

do{

number++；

if(number!=10&&number!=11)

sum+=number;

)

while(number<20);

System.out.println("Thesumis"+sum);

)

}

14.Thestatementlabelednext.

15.Thecontrolisintheouterloop,andthenextiterationoftheouterloopisexecuted.

16.

Line3:Thesemicolon(;)attheendoftheforloopheadingshouldberemoved.

Line4:sumnotdefined.

Line5:thesemicolon(;)attheendoftheifstatementshouldberemoved.

Line6:Missingasemicolonforthefirstprintinstatement.

Une6:jnotdefined.

Line10:Thesemicolon(;)attheendofthewhileheadingshouldberemoved.

Line17:Missingasemicolonattheendofthewhileloop.

17.

(A)compileerror:iisnotinitialized.

(B)Line3:The;attheendofforloopshouldberemoved.

for(inti=0;i<10;i++);

18.

(A).0010120123

(B)********2****32****432****

(C).Ixxx2xxx4xxx8xxxl6xxxIxxx2xxx4xxx8xxxIxxx2xxx4xxxlxxx2xxxlxxx

(D).1G1G3G1G3G5G1G3G5G7G1G3G5G7G9G

19.

(A)

publicclassTest{

publicstaticvoidmain(String[]args){

inti=0;

if(i>0)

i++；

else

chargrade;

if(i>=90)

grade='A';

elseif(i>=80)

grade=B;

)

}

(B)

publicclassTest{

publicstaticvoidmain(String[]args){

for(inti=0;i<10;i++)

if(i>0)

i++;

else

Ch叩ter5Methods

1.Atleastthreebenefits:(1)Reusecode;(2)Reducecomplexity;(3)Easytomaintain.

SeetheSections4.2and4.3onhowtodeclareandinvokemethods.

2.void

3.Yes.return(numl>num2)?numl:num2;

4.

True:acalltoamethodwithavoidreturntypeisalwaysastatementitself.

False:acalltoamethodwithanonvoidreturntypeisalwaysacomponentofan

expression.

5.Asyntaxerroroccursifareturnstatementdoesnotappearinanon-voidmethod.Youcan

haveareturnstatementinavoidmethod,whichsimplyexitsthemethod.Butareturnstatement

cannotreturnavaluesuchasreturnx+yinavoidmethod.

6.SeeSection5.2.

7.

Computingasalescommissiongiventhesalesamountandthecommissionrate

publicstaticdoublegetCommission(doublesalesAmount,double

commissionRate)

Printingacalendarforamonth

publicstaticvoidprintCalendar(intmonth,intyear)

Computingasquareroot

publicstaticdoublesqrt(doublevalue)

Testingwhetheranumberisevenandreturntrueifitis

publicstaticbooleanisEven(intvalue)

Printingamessageforaspecifiednumberoftimes

publicstaticvoidprintMessage(Stringmessage,inttimes)

Computingthemonthlypayment,giventheloanamount,

numberofyears,andannualinterestrate.

publicstaticdoublemonthlyPayment(doubleloan,int

numberOfYears,doubleannuallnterestRate)

Findingthecorrespondinguppercaselettergivenalowercaseletter,

publicstaticchargetUpperCase(charletter)

8.

Line2:methodiisnotdefinedcorrectly.Itdoesnothaveareturntypeorvoid.

Line2:typeintshouldbedeclaredforparameterm.

Line8:parametertypefornshouldbedoubletomatchxMethod(3.4).

Line11:if(n<0)shouldberemovedinxMethod,otherwisetheacompilation

errorisreported.

9.

publicclassTest{

publicstaticdoublexMethod(doublei,doublej){

while(i<j){

j-；

}

returnj;

}

}

10.Youpassactualparametersbypassingtherighttypeofvalueintherightorder.Theactual

parametercanhavethesamenameasitsformalparameter.

11."Passbyvalue"istopassacopyofthevaluetothemethod.

(A)Theoutputoftheprogramis0,becausethevariablemaxisnotchangedby

invokingthemethodmax.

(B)Beforethecall,variabletimesis3

n=3

WelcometoJava!

n=2

WelcometoJava!

n=1

WelcometoJava!

Afterthecall,variabletimesis3

(C)

2

24

248

24816

2481632

248163264

①)

1

21

21

421

iis5

12.

Justbeforemaxis

invoked.

Spacerequiredforthe

mainmethod

max:0

Justenteringmax.

Spacerequiredforthe

maxmethod

max:0value2:2valuel:lJustbeforemaxis

returned

Spacerequiredforthe

mainmethod

max:0

Spacerequiredforthe

maxmethod

max:2value2:2valuel:ISpacerequiredforthe

mainmethod

max:OSpacerequiredforthe

mainmethod

max:0

Rightaftermaxis

returned

13.Twomethodswiththesamename,definedinthesameclass,iscalledmethodoverloading.It

isfinetohavesamemethodname,butdifferentparametertypes.Youcannotoverloadmethods

basedonreturntype,ormodifiers.

14.Methodspublicstaticvoidmethod(intx)andpublicstaticintmethod(inty)havethesame

signaturemethod(int).

15.Line8:intn=1iswrongsincenisalreadydeclaredinthemethodsignature.

16.True

17.

(a)34+(int)(Math.random()*(55-34))

(b)(int)(Math.random()*1000)

(c)5.5+(Math.random()*(55.5-5.5))

(d)(char)(H+(Math.random()*(N-'a，+1))

18.

Math.sqrt(4)=2.0

Math.sin(2*Math.PI)=0

Math.cos(2*Math.PI)=1

Math.pow(2,2)=4.0

Math.log(Math.E)=1

Math.exp(l)=2.718

Math.max(2,Math.min(3,4))=3

Math.rint(-2.5)=-2.0

Math.ceil(-2.5)=-2.0

Math.floor(-2.5)=-3.0

Math.round(-2.5f)=-2

Math.round(-2.5)=-2

Math.rint(2.5)=2.0

Math.ceil(2.5)=3.0

Math.floor(2.5)=2.0

Math.round(2.5f)=3

Math.round(-2.5)=-2

Math.round(Math.abs(-2.5))=3

19.Threebenefits:(1)toavoidnamingconflicts.(2)todistributesoftwareconveniently.

(3)Toprotectclasses.

20.Thesourcecode.javafileshouldbestoredinanyDir\java\chapter4,andtheclassfilemaybe

storedinanyOtherDir\java\chapter4.The.javafileand.classmaybeinthesamedirectoryora

differentdirectory.SoanyDirandanyOtherDirmaybesameordifferent.Tomaketheclass

available,addanyOtherDirintheclassspathusingthecommand

setclasspath=%classpath%;anyOtherDir

21.TheMathclassisinthejava.langpackage.Anyclassinthejava.langpackageisautomatically

imported.Sothereisnoneedtoimportitexplicitly.

Chapter6Arrays

1.Seethesection"DeclaringandCreatingArrays."

2.Youaccessanarrayusingitsindex.

3.Nomemoryisallocatedwhenanarrayisdeclared.Thememoryisallocatedwhencreatingthe

array,xis60Thesizeofnumbersis30

4.Indicatetrueorfalseforthefollowingstatements:

1.Everyelementinanarrayhasthesametype.Answer:True

2.Thearraysizeisfixedafteritisdeclared.Answer:False

3.Thearraysizeisfixedafteritiscreated.Answer:True

4.Theelementinthearraymustbeofprimitivedatatype.Answer:False

5.Whichofthefollowingstatementsarevalidarraydeclarations?

inti=newint(30);Answer:Invalid

doubled[]=newdouble[30];Answer:Valid

char[]r=newchar(1..3O);Answer:Invalid

inti[]=(3,4,3,2);Answer:Invalid

floatf[]={2.3,4.5,5.6};Answer:Valid

char[]c=newchar();Answer:Invalid

6.Thearrayindextypeisintanditslowestindexis0.

7.a[2]

8.Aruntimeexceptionoccurs.

9.

Line3:thearraydeclarationiswrong.Itshouldbedoublet].Thearrayneedsto

becreatedbeforeitsbeenused.e.g.newdouble[10]

Line5:Thesemicolon(;)attheendoftheforloopheadingshouldberemoved.

Line5:r.length()shouldber.length.

Line6:randomshouldberandom()

Line6:r(i)shouldber[i].

10.System.arraycopy(source,0,t,0,source.length);

11.ThesecondassignmentstatementmyList=newint[20]createsanewarrayand

assignsitsreferencetomyList.

myListnewint[10]Array

myListnewint[10]Array

newint[20]Array

12.False.Whenanarrayispassedtoamethod,thereferencevalueofthearrayispassed.No

newarrayiscreated.Bothargumentandparameterpointtothesamearray.

13.numbersis0andnumbers[0]is3

14.

Spacerequiredforthe

displayArraymethod

char[]chars:re

A)ESpacerequiredforthe

mainmethod

char[]chars:ref

Heap

Arrayof100

characters

Spacerequiredforthe

createArraymethod

char[]chars:ref

(B)

Spacerequiredforthe

mainmethod

char[]chars:refHeapArrayof100

characters

StackStack

C)ESpacerequiredforthe

mainmethod

char[]chars:ref

Heap

Arrayof100

charactersf

(D)

Spacerequiredforthe

mainmethod

char[]chars:refHeapArrayof100

characters

StackStack

E)ESpacereqidredforthe

mainmethod

int[]counts:ref

char[]chars:ref

Heap

Arrayof100

characters

Spacerequiredforthe

countLettersmethod

int[]counts:ref

char[]chars:ref

(F)

Spacerequiredforthe

mainmethod

int[]counts:refchar[]chars:refHeapArrayof100

characters

StackStack

Arrayof26

integers

Arrayof26

integers

G)ESpacerequiredforthe

mainmethod

int[]counts:ref

char[]chars:ref

Heap

Arrayof100

characters

Spacerequiredforthe

displaycounts

method

int[]counts:ref

(H)

Spacerequiredforthe

mainmethod

int[]counts:refchar[]chars:refHeapArrayof100

characters

StackStack

Arrayof26

integers

Arrayof26

integers

15.Onlyonevariable-lengthparametermaybespecifiedinamethodandthisparametermustbe

thelastparameter.Themethodreturntypecannotbeavariable-lengthparameter.

16.Thelastone

printMax(newint[]{l,2,3});

isincorrect,becausethearraymustofthedoublet]

type.

17.Omitted

18.Omitted

19.Omitted

20Simplychange(currentMax<list[j])onLine10to

(currentMax>list[j])

21Simplychangelist[k]>currentElementonLine9to

list[k]<currentElement

22.Toapplyjava.util.Arrays.binarySearch(array,key),thearraymustbesortedinincreasingorder.

23.Youcansortanarrayofanyprimitivetypesexceptboolean.Thesortmethodisvoid,soit

doesnotreturnanewarray.

24.

Line1:listis[2,4,7,10}

Line2:listis{7,7,7,7}

Line3:listis{7,8,8,7}

Line4:listis{7,8,8,7}

25int[][]m=newint⑷⑸；

26Yes.Theyareraggedarray.

27array[0][l]is2.

28.

r=newint[2];

int[][]Answer:Invalid

=newint[];

int[]xAnswer:Invalid

int[][]y=newint[3][];Answer:Valid

Chapter7ObjectsandClasses

1.Seethesection"DeclaringandCreatingObjects."

2.Constructorsarespecialkindsofmethodsthatarecalledwhencreatinganobjectusingthe

newoperator.Constructorsdonothaveareturntype—notevenvoid.

3.Anarrayisanobject.Thedefaultvaluefortheelementsofanarrayis0fornumeric,falsefor

boolean,'XuOGOO'forchar;nullforobjectelementtype.

4.

(a)ThereissuchconstructorShowErrors(int)intheShowErrorsclass.

TheShowErrorsclassinthebookhasadefaultconstructor.Itisactuallysameas

publicclassShowErrors{

publicstaticvoidmain(String[]args){

ShowErrorst=newShowErrors(5);

}

publicShowErrors(){

)

}

OnLine3,newShowErrors(5)attemptstocreateaninstanceusingaconstructorShowErrors(int),

buttheShowErrorsclassdoesnothavesuchaconstructor.Thatisanerror.

(b)x()isnotamethodintheShowErrorsclass.TheShowErrorsclassinthebookhasadefault

constructor.Itisactuallysameas

publicclassShowErrors{

publicstaticvoidmain(String[]args){

ShowErrorst=newShowErrors();

t.x();

)

publicShowErrors(){

)

)

OnLine4,t.x()isinvoked,buttheShowErrorsclassdoesnothavethemethodnamedx().Thatis

anerror.

(c)Theprogramcompilesfine,butithasaruntimeerrorbecausevariablecisnullwhenthe

printinstatementisexecuted.

(d)newC(5.0)doesnotmatchanyconstructorsinclassC.Theprogramhasacompilationerror

becauseclassCdoesnothaveaconstructorwithadoubleargument.

5.TheprogramdoesnotcompilebecausenewA()isusedinclassTest,butclassAdoesnothave

adefaultconstructor.SeethesecondNOTEintheSection,^Constructors/

6.false

7.UsetheDate'sno-argconstructortocreateaDateforthecurrenttime.UsetheDate'stoString()

methodtodisplayastringrepresentationfortheDate.

8.UsetheJFrame'sno-argconstructortocreateJFrame.UsethesetTitle(String)methodaseta

titleandusethesetVisible(true)methodtodisplaytheframe.

9.Dateisinjava.util.JFrameandJOptionPaneareinjavax.swing.SystemandMatharein

java.lang.

10.

System.out.println(f.i);Answer:Correct

System.out.println(f.s);Answer:Correct

f.imethod();Answer:Correct

f.smethod();Answer:Correct

System.out.println(Foo.i);Answer:Incorrect

System.out.println(Foo.s);Answer:Correct

Foo.imethod();Answer:Incorrect

Foo.smethod();Answer:Correct

11.Addstaticinthemainmethodandinthefactorialmethodbecausethesetwomethodsdon't

needreferenceanyinstanceobjectsorinvokeanyinstancemethodsintheTestclass.

12.Youcannotinvokeaninstancemethodorreferenceaninstancevariablefromastaticmethod.

Youcaninvokeastaticmethodorreferenceastaticvariablefromaninstancemethod?cisan

instancevariable,whichcannotbeaccessedfromthestaticcontextinmethod2.

13.Accessormethodisforretrievingprivatedatavalueandmutatormethodisforchanging

privatedatavalue.ThenamingconventionforaccessormethodisgetDataFieldName()for

non-booleanvaluesandisDataFieldName()forbooleanvalues.Thenamingconventionfor

mutatormethodissetDataFieldName(value).

14.Twobenefits:(1)forprotectingdataand(2)foreasytomaintaintheclass.

15.Yes.Thoughradiusisprivate,myCircle.radiusisusedinsidetheCircleclass.Thus,itisfine.

16.No.Itmustalsocontainnogetmethodsthatwouldreturnareferencetoamutabledatafield

object.

17.Yes.

18.Javauses“passbyvalue“topassparameterstoamethod.Whenpassingavariableofa

primitivetypetoamethod,thevariableremainsunchangedafterthemethodfinishes.However,

whenpassingavariableofareferencetypetoamethod,anychangestotheobjectreferencedby

thevariableinsidethemethodarepermanentchangestotheobjectreferencedbythevariable

outsideofthemethod.Boththeactualparameterandtheformalparametervariablesreference

tothesameobject.

Theoutputoftheprogramisasfollows:count101times0

19.

Remark:Thereferencevalueofcirclelispassedtoxandthereferencevalueofcircle?ispassed

toy.Thecontentsoftheobjectsarenotswappedintheswaplmethod,circlelandcircle?are

notswapped.Toactuallyswapthecontentsoftheseobjects,replacethefollowingthreelines

Circletemp=x;

x=y;

y=temp;

by

doubletemp=x.radius;

x.radius=y.radius;

y.radius=temp;

asinswap2.

20.

a.a[0]=1a[l]=2

b.a[0]=2a[l]=l

c.el=2e2=1

d.tl/si=2tl/sj=l

t2/si=2t2/sj=l

21.i+jis23(becausei(valueof2)isconcatenatedwithstringj+jis,thenj(valueof3)is

concatenatedwithstringi+jis2.)kis2jis0

22.Seethesectiononthethiskeyword.Thevalueofparameterpisassignedtoparameterpin

Line5.Itshouldbethis.p=p;

23.(Line4printsnullsincedates[0]isnull.Line5causesaNullPointerExceptionsinceitinvokes

toString()methodfromthenullreference.)

24.No.TheLoanclasshasthegetLoanDate()methodthatreturnsloanDate.loanDateisanobject

oftheDateclass.SinceDateismutable,thecontentsofloanDatecanbechanged.So,theLoan

classisnotimmutable.

25.TheStackOfIntegerclassisimmutable,becausethecontentsofastackcanbechanged

throughthepopandpushmethods.

Chapter8StringsandTextI/O

1.

si==s2=>true

s2==s3=>false

sl.equals(s2)=>true

s2.equals(s3)=>true

pareTo(s2)=>0

pareTo(s3)=>0

si==s4=>true

sl.charAt(O)=>W

sl.indexOf('j')=>-1

sl.indexOf("to")=>8

sl.lastlndexOf('a')=>14

sl.lastlndexOf("o",15)=>9

sl.length()=>16

sl.substring(5)=>metoJava!

sl.substring(5,11)=>meto

sl.startsWith("Wel")=>true

sl.endsWith("Java")=>true

sl.toLowerCase()=>welcometojava!

sl.toUpperCase()=>WELCOMETOJAVA!

"Welcome".trim()=>Welcome

sl.replace('o',T)=>WelcTmetTJava!

sl.replaceAII("o","T")=>WelcTmetTJava!

sl.replaceFirst("o"z"T")=>WelcTmetTJava!

sl.toCharArray()returnsanarrayofcharactersconsistingofW,e,I,c,o,m,e,,t,o,,J,a,v,a

(Notethatnoneoftheoperationcausethecontentsofastringtochange)

2.

Strings=newString("newstring");Answer:Correct

Strings3=si+s2;Answer:Correct

Strings3=si-s2;Answer:Incorrect

si==s2Answer:Correct

si>=s2Answer:Incorrect

pareTo(s2);Answer:Correct

inti