面向对象编程题目.docx
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面向对象编程题目
面向对象编程
（1）
GiventhefollowingJavacode:
classAnimal{publicStringnoise（）{return"peep"}}
classDogextendsAnimal{
publicStringnoise（）{return"back";}
}
classCatextendsAnimal{
publicStringnoise（）{return"move";}
}
...
Animalanimal=newDog（）;
Catcat=（Cat）animal;
System.out.printIn（cat.noise（））;
Whatistheresult?
A.peep
B.back
C.move
D.Compilationfails.
E.Anexceptionisthrownatruntime
（2）
GiventhefollowingJavacode:
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interfaceA{publicintgetValue（）;}
classBimplementsA{
publicintgetValue（）{return1;}
}
classCextendsB{
//insertcodehere
}
Whatthreecodefragmentsinsertedindividuallyatline15,makeusedofpolymorphism?
（choosethree）
A.publicvoidadd（Cc）{c.getValue（）;}
B.publicvoidadd（Bb）{b.getValue（）;}
C.publicvoidadd（Aa）{a.getValue（）;}
D.publicvoidadd（Aa,Bb）{a.getValue（）;}
E.publicvoidadd（Cc1Cc2）{c1.getValue（）;}
（3）
AddmethodstotheBetaclasstomakeitcompilecorrectly.
classAlpha{
publicvoidbar（int…x）{}
publicvoidbar（intx）{}
}
publicclassBetaextendsAlpha{
placehere
placehere
placehere
}
Methods
privatevoidbar（intx）{}
publicvoidbar（intx）{}
publicintbar（Stringx）{return1;}
publicAlphabar（intx）{}
publicvoidbar（intx,inty）{}
publicintbar（intx）{returnx;}
（4）
GiventhefollowingJavacode:
classTest1{
publicTest1foo（）{returnthis;}
}
classTest2extendsTest1{
publicTest1foo（）{returnthis;}
}
classTest3extendsTest2{
//insertmethodhere
}
Whichtwomethods,insertedindividually,correctlycompletetheTest3class?
（choosetwo）
A.publicvoidfoo（）{}
B.publicintfoo（）{return3;}
C.publicTest2foo（）{returnthis;}
D.publicTest1foo（）{returnthis;}
（5）
GiventhefollowingJavacode:
publicclassBootchy{
intbootch;
Stringsnootch;
publicBootchy（）{
this（"snootchy"）;
System.out.print（"first"）;
}
publicBoothchy（Stringsnootch）{
this（420,"snootchy"）;
System.out.print（"second"）;
}
publicBootchy（intbootch,Stringsnootch）{
this.bootch=bootch;
this.snootch=snootch;
System.out.print（"third"）;
}
publicstaticvoidmain（String[]args）{
Bootchyb=newBootchy（）;
System.out.print（b.snootch+""+b.bootch）;
}
}
Whatistheresult?
（运行结果）
（6）
GiventhefollowingJavacode:
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publicclassTest{
staticclassA{
voidprocess（）throwsException{thrownewException（）;}
}
staticclassBextendsA{
voidprocess（）{System.out.println（"B"）;}
}
publicstaticvoidmain（String[]args）{
Aa=newB（）;
a.process（）;
}
}
Whatistheresult?
A.B
B.Thecodeexceptionisthrownatruntime（执行时抛出exception）
C.Thecoderunwithnooutput（沒有任何输出）
D.Compilationfailsbecauseofanerrorinline15.
E.Compilationfailsbecauseofanerrorinline18.
F.Compilationfailsbecauseofanerrorinline19.
（7）
GiventhefollowingJavacode:
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interfaceFoo{}
classAlphaimplementsFoo{}
classBetaextendsAlpha{}
classDeltaextendsBeta{
publicstaticvoidmain（String[]args）{
Betax=newBeta（）;
//insertcodehere
}
}
Whichcode,insertedatline16willcauseajava.lang.ClassCastException?
A.Alphaa=x;
B.Foof=（Delta）x;
C.Foof=（Alpha）x;
D.Betab=（Beta）（Alpha）x;
（8）
GiventhefollowingJavacode:
publicclassPerson{
privateStringname,comment;
privateintage;
publicPerson（Stringn,inta,Stringc）{
name=n;age=a;comment=c;
}
publicBooleanequals（Objecto）{
if（!
（oinstanceofPerson））returnfalse;
Personp=（Person）o;
returnage==p.age&&name.equals（p.name）;
}
}
WhatistheappropriateddefinitionofthehashCodemethodinclassPerson?
A.returnsuper.hashCode（）;
B.returnname.hashCode（）+age*7;
C.returnnamehashcode（）+comment.hashCode（）/2;
D.returnname.hashCode（）+comment.hashCode（）/2-age*3;
（9）
Giventhefollowingcode:
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publicclassPerson{
privateStringname;
publicPerson（Stringname）{this.name=name;}
publicBooleanequals（Personp）{
returnp.name.equals（this.name）;
}
}
Whichstatementistrue?
A.TheequalsmethoddoesNOTproperlyoverridetheobjectObject.equalsmethod.
B.Compilationfailsbecausetheprivateattributep.namecannotbeaccessedinline5.
C.Toworkcorrectlywithhash-baseddatastructures,thisclassmustalsoimplementthehashCodemethod.
D.WhenaddingPersonobjectstojava.util.Setcollection,theequalsmethodinline4willpreventduplicates.
（10）
PlacetheOutputOptionsintheActualOutputSequencetoindicatetheoutputfromthiscode:
classAlpha{
publicvoidfoo（String...args）{
System.out.print（"Alpha:
foo"）;
}
publicvoidbar（Stringa）{
System.out.print（"Alpha:
bar"）;
}
}
publicclassBetaextendsAlpha{
publicvoidfoo（Stringa）{
System.out.print（"Beta:
foo"）;
}
publicvoidbar（Stringa）{
System.out.print（"Beta:
bar"）;
}
publicstaticvoidmain（String[]args）{
Alphaa=newBeta（）;
Betab=（Beta）a;
a.foo（"test"）;
b.foo（"test"）;
a.bar（"test"）;
b.bar（"test"）;
}
}
ActulOutputSequence:
Placehere
Placehere
Placehere
Placehere
OutputOption:
Alpha:
foo
Alpha:
bar
Beta:
foo
Beta:
bar
（11）
GiventhefollowingJavacode:
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publicinterfaceA{
publicvoiddoSomething（Stringthing）;
}
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publicclassAImp1implementsA{
publicvoiddoSomething（Stringmsg）{}
}
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publicclassB{
publicAdoit（）{
//morecodehere
}
publicStringexecute（）{
//morecodehere
}
}
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publicclassCextendsB{
publicAImp1doit（）{
//morecodehere
}
publicObjectexecute（）{
//morecodehere
}
}
Whichstatementistrueabouttheclassandinterfacesinthis"Code"?
A.Compilationwillsucceedforallclassesandinterfaces.
B.CompilationofclassCwillfailbecauseofanerrorintline2.
C.CompilationofclassCwillfailbecauseofanerrorintline6.
D.CompilationofAImplwillfailbecauseofanerrorinline2.
（12）
GiventhefollowingJavacode:
classA{
Stringname="A";
StringgetName（）{
returnname;
}
Stringgreeting（）{
return"classA";
}
}
classBextendsA{
Stringname="B";
Stringgreeting（）{
return"classB";
}
}
publicclassClient{
publicstaticvoidmain（String[]args）{
Aa=newA（）;
Ab=newB（）;
System.out.println（a.greeting（）+"hasname"+a.getName（））;
System.out.println（b.greeting（）+"hasname"+b.getName（））;
}
}
Placethenames"A"and"B"inthefollowingoutput.
ClassPlaceherehasnamePlacehere
ClassPlaceherehasnamePlacehere
Names:
A
B
（13）
GiventhefollowingJavacode:
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classSuperClass{
publicAgetA（）{
returnnewA（）;
}
}
classSubClassextendsSuperClass{
publicBgetA（）{
returnnewB（）;
}
}
Whichstatementistrue?
A.CompilationwillsucceedifAextendsB
B.CompilationwillsucceedifBextendsA
C.Compilationwillalwaysfailbecauseofanerrorinline7
D.Compilationwillalwaysfailbecauseofanerrorinline8
（14）
GiventhefollowingJavacode:
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classPizza{
java.util.ArrayListtoppings;
publicfinalvoidaddTopping（Stringtopping）{
toppings.add（topping）;
}
}
publicclassPepperoniPizzaextendsPizza{
publicvoidaddTopping（Stringtopping）{
System.out.println（"CannotandUoppings"）;
}
publicstaticvoidmain（String[]args）{
Pizzapizza=newPepperoniPizza（）;
Pizza.addTopping（"Mushrooms"）;
}
}
Whatistheresult?
A.Compilationfails
B.CannotandUoppings
C.Thecoderunswithnooutput
D.ANullPointerExceptionisthrowninLine4
（15）
GiventhefollowingJavacode:
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interfaceA{
voidx（）;
}
classBimplementsA{
publicvoidx（）{}
publicvoidy（）{}
}
classCextendsB{
publicvoidx（）{}
}
And:
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java.util.Listlist=newjava.util.ArrayList（）;
list.add（newB（））;
list.add（newC（））;
for（Aa:
list）{
a.x（）;
a.y（）;
}
Whatistheresult?
A.Thecoderunswithnooutput
B.Anexceptionthrownatruntime
C.Compilationfailsbecauseofanerrorinline20
D.Compilationfailsbecauseofanerrorinline21
E.Compilationfailsbecauseofanerrorinline23
F.Compilationfailsbecauseofanerrorinline25
（16）
GiventhefollowingJavacode:
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classOne{
voidfoo（）{}
}
classTwoextendsOne{
//insertmethodhere
}
Whichthreemethods,insertedindividuallyatline14willcorrectlyclassTwo?
（Choosethree）
A.intfoo（）{/*morecodehere*/}
B.voidfoo（）{/*morecodehere*/}
C.publicvoidfoo（）{/*morecodehere*/}
D.privatevoidfoo（）{/*morecodehere*/}
E.protectedvoidfoo（）{/*morecodehere*/}
（17）
WhichtwostatementsaretrueaboutthehashCodemethod?
（Choosetwo）
A.ThehashCodemethodforagivenclasscanbeusedtotestforobjectequalityandobjectinequalityforthatclass.（hashCodemethod
B.ThehashCodemethodisusedbythejava.util.SortedSetcollectionclasstoordertheementswithinthatset.
C.ThehashCodemethodforagivenclasscanbeusedtotestforobjectinequality,butNOTobjectequalityforthatclass.
D.TheonlyimportantcharacteristicofthevaluesreturnedbyahashCo
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