Java語言程序設(shè)計(jì)(鄭莉)第四章課后習(xí)題答案

1、Java語言程序設(shè)計(jì)第四章課后習(xí)題答案1.子類將繼承父類所有的屬性和方法嗎？為什么？答：不,子類不能直接訪問從父類中繼承的私有屬性及方法，但可以對(duì)公有及保護(hù)方法進(jìn)行訪問。2.方法的覆蓋與方法的重載有何不同？答：覆蓋是運(yùn)用在子類中實(shí)現(xiàn)與父類相同的功能，但采用不同的算法或公式；在名字相同的方法中，要做比父類更多的事情；在子類中需要取消從父類繼承的方法。3聲明兩個(gè)帶有無參構(gòu)造方法的兩個(gè)類A和B,聲明A的子類C,并且聲明B為C的一個(gè)成員，不聲明C的構(gòu)造方法。編寫測試代碼，生成類C的實(shí)例對(duì)象，并觀察結(jié)果。/A類publicclassApublicA()System.out.println(輸出A類)；/

2、B類publicclassBpublicB()System.out.println(輸出B類)；/C類publicclassCextendsABb=newB()；/測試類publicclasstest4_3publicstaticvoidmain(Stringargs)Cc=newC()；運(yùn)彳丁結(jié)果：,Problems自四日仃匸terminatedte*&t4_3Java輸出A類輸出萬類4聲明一個(gè)基類A,它只有一種非默認(rèn)構(gòu)造方法；聲明A的子類B,B具有默認(rèn)方法及非默認(rèn)方法，并在B的構(gòu)造方法中調(diào)用基類A的構(gòu)造方法。/A類publicclassApublicA(Stringlin)System.o

3、ut.println(A類的非默認(rèn)構(gòu)造方法+lin);/B類publicclassBextendsApublicB()super(Fuckyourteacher);System.out.println(B默認(rèn)類構(gòu)造方法);publicB(Stringlin)super(lin);System.out.println(B類非構(gòu)造方法);/測試類publicclasstest4_4publicstaticvoidmain(Stringargs)newB();System.out.println();newB(Fuckmyteacher);運(yùn)行結(jié)果,ProLlamsTJavado-c凰Declara

4、lion冃CorterminatedHe5t4_4JavaApplicationD:Prograi負(fù)類的非默認(rèn)構(gòu)鑿方法yoarteacherE默認(rèn)類構(gòu)苣方法直類的車監(jiān)認(rèn)構(gòu)苣方法FjcJemvteacrierE類非構(gòu)直方法5.聲明一個(gè)類，它具有一種方法，此方法被重載三次，派生一個(gè)新類，并增加一種新的重載方法，編寫測試類驗(yàn)證四種方法對(duì)于派生類驗(yàn)證四種方法對(duì)于派生類都有效。/A類publicclassApublicvoidshowTime()System.out.println(空重載);publicvoidshowTime(intl)System.out.println(整形參數(shù)重載);publi

5、cvoidshowTime(charl)System.out.println(字符參數(shù)重載);B類publicclassBextendsApublicvoidshowTime(Stringl)System.out.println(字符串參數(shù)重載);/測試類publicclasstest4_5publicstaticvoidmain(Stringargs)Bb=newB();b.showTime();b.showTime(5);b.showTime(f);b.showTime(林楚金);,ProLlernsavadoc鷹terminatedteet4_5JavaA|：空重載整砒卷數(shù)重載宇紆參埶重

6、載字符串蜃數(shù)重載6聲明一個(gè)具有final方法的類，聲明一個(gè)派生類，并試圖對(duì)這個(gè)方法進(jìn)行重寫，會(huì)有什么結(jié)果。/A類publicclassApublicfinalvoidshowTime()System.out.println(類A中方法);/B類publicclassBextendsApublicvoidshowTime()System.out.println(類B中方法);/測試類publicclasstest4_6publicstaticvoidmain(Stringargs)Bb=newB();b.showTime();運(yùn)行結(jié)果：.ProblemsJavadoc.DeclarationCo

7、nsole.Problemsterminatedtest4_6JavaApplicationD:ProgramFilesMyEclipseB.Ojrebinjavav.exe(Apr12,20111;19:44AM)ExceptioninthreadITmaLinrrjava.FeTlfyEHfoir:classBoverridesfinslJLmsttiDd.匚a匸javalanguClassXoaderdexneClassi(KTmt1工?已劇已匸比口d.auava：LRiig匸丄呂5：3工口日1已2cl巳工丄n巳Cl且ss(UnJcnciTriSource)atjava巴亡匚;1工:1匕

8、5亡匚口工皂二1且ssLo且浬亡:rd皂:fin亡f1且ss(UiHm購nSourc皂)atjavane!七URL1el日耳匸diaii皀聲込色匸丄玄龍m(nlcroxmSource)atava：i亡匸.URLClassLoaieribcuess車丄oo(umcrgumsource)atjava：i亡匸.URLClassLaaderS-ltunlDnlEnciwnSourc皂)atjavasecjizityAccessCcn.czoilerdoPrivi1egediLveblmthod)atjavs.：i亡匕urlcj_eleisjl且3皂工工丄ndClelssUaJercnmsource)a

9、tjava1己nor.ClassloaderSource)bl匸suzimiEUI.ELJLnc5h啟直fJippClaL日mlosLie：匱丄caaLdClaLSJE!(Unkniown.Source)atjava1己ngCJLia呂尋LdslcL皂tloiadClass(UnknownSource)-atjava丄込11口.Clia呂卻工口且小亡：lD；adEla迅且工nt已工nal(CJDkncnwriSource)attest46mcLxn.|匸芒n匸2E=uviB:q)(說白了就是B中showTime()的無法覆蓋A中showTime(),被覆蓋為final,不能覆蓋。)7聲明一個(gè)f

10、inal類，并試圖聲明其派生類，會(huì)有什么結(jié)果。/A類publicfinalclassA/B類publicclassBextendsA/測試類publicclasstest4_7publicstaticvoidmain(Stringargs)Bb=newB();運(yùn)行結(jié)果：蹩Pr&blemsavadoc陰Declaration同Console21&514_7JavaAoplicationD:PrcgramFlesMyEclipse6.0jrebinjavaw.exe（Apr12,2011124:11AM）EfEceptloninthxeadrTmain,Tjava1ang.Error:Unreso

11、lvedcompxlatDnprobiera:Thetype3匸且imotanibcl且3日thefin且1classA且匸te3tx.getscoreOfsum()System.out.println(this.getname()+總分大于+x.getname();if(this.getscoreOfsum()x.getscoreOfsum()System.out.println(this.getname()+總分小于+x.getname();elseSystem.out.println(this.getname()+總分等于+x.getname();/equals方法/比較2學(xué)生學(xué)號(hào)是否相

12、等(還沒完善)/*publicbooleanequals(Objectx)if(this.getClass()!=x.getClass()returnfalse;Studentb=(Student)x;if(this.id=b.getid()returntrue;*/（2）聲明StudentXW（學(xué)習(xí)委員）類為Student類的子類。在StudentXW類中增加責(zé)任屬性，并重寫testScore方法（評(píng)測成績=三門課平均分+3）publicclassStudentXWextendsStudentStringresponsibility;/構(gòu)造方法publicStudentXW()super()

13、;/responsibility=;publicStudentXW(Stringaid,Stringaname,floatascoreOfenglish,floatascoreOfmath,floatascoreOfcomputer,Stringaresponsibility)super(aid,aname,ascoreOfenglish,ascoreOfmath,ascoreOfcomputer);responsibility=aresponsibility;/testScore測評(píng)成績/平均分publicfloattestScore()return(this.scoreOfsum/3+3)

14、;/toString方法publicStringtoString()return(學(xué)號(hào)：+this.id+n姓名：+name+n英語：+this.scoreOfenglish+n數(shù)學(xué)：+this.scoreOfmath+n計(jì)算機(jī)：+this.scoreOfcomputer+n總分：+this.scoreOfsum+n職位：+this.responsibility);(3)聲明StudentBZ類為Student類的子類在StudentBZ類中增加責(zé)任屬性，并重寫testScore方法(評(píng)測成績=三門課平均分+5)publicclassStudentBZextendsStudentStringr

15、esponsibility;/構(gòu)造方法publicStudentBZ()super();/responsibility=;publicStudentBZ(Stringaid,Stringaname,floatascoreOfenglish,floatascoreOfmath,floatascoreOfcomputer,Stringaresponsibility)super(aid,aname,ascoreOfenglish,ascoreOfmath,ascoreOfcomputer);responsibility=aresponsibility;/testScore測評(píng)成績/平均分public

16、floattestScore()return(this.scoreOfsum/3+5);/toString方法publicStringtoString()return(學(xué)號(hào)：+this.id+n姓名：+name+n英語：+this.scoreOfenglish+n數(shù)學(xué)：+this.scoreOfmath+n計(jì)算機(jī)：+this.scoreOfcomputer+n總分：+this.scoreOfsum+n職位：+this.responsibility);4）聲明測試類，生成若干個(gè)Student類、StudentXW類及StudentBZ類對(duì)象，并分別計(jì)算它們的評(píng)測成績（建議采用:寫一個(gè)測試函數(shù)，該

17、函數(shù)以父類student數(shù)組作為參數(shù)）。importjava.text.*;publicclasstest4_10publicstaticvoidmain(Stringargs)Studentsu=newStudent(001,蘇軾,56.00f,87.00f,95.00f);Studentdu=newStudent(002,杜甫,86.00f,75.00f,80.00f);Studentbai=newStudent(003,白居易,42.00f,77.00f,65.00f);Studentliu=newStudent(004,柳宗元,67.00f,67.00f,67.00f);Student

18、XWou=newStudentXW(005,歐陽修,89.00f,98.00f,90.00f,數(shù)學(xué)代表)；StudentXWwang=newStudentXW(006,王安石,98.00f,87.00f,36.00f,英語代表);StudentBZli=newStudentBZ(007,李白,89.00f,87.00f,87.00f,班長”)；System.out.print(li);System.out.println(n評(píng)測成績System.out.println();System.out.print(wang);System.out.println(n評(píng)測成績System.out.pri

19、ntln();System.out.print(ou);System.out.println(n評(píng)測成績System.out.println();System.out.print(su);II+newDecimalFormat(0.00).format(li.testScore();II+newDecimalFormat(0.00).format(wang.testScore();II+newDecimalFormat(0.00).format(ou.testScore();3333System.out.println(n評(píng)測成績System.out.println();System.out.print(du);System.out.println(n評(píng)測成績System.out.println();System.out.print(bai);System.out.println(n評(píng)測成績System.out.println();System.out.print(liu);System.out.println(n評(píng)測成績：+newDecimalFormat(0.00).format(su.testScore();：+newDecimalFormat(0.00).format(du.testScor