Betax=newBeta();

//insertcodehere

}

}

Whichcode,insertedatline16,willcauseajava.lang.ClassCastException?

Alphaa=x;

Foof=(Delta)x;

Foof=(Alpha)x;

Betab=(Beta)(Alpha)x;

Question4

WhichManclassproperlyrepresentstherelationship“ManhasabestfriendwhoisaDog”?

classManextendsDog{}

classManimplementsDog{}

classMan{privateBestFrienddog;}

classMan{privateDogbestFriend;}

classMan{privateDog<bestFriend>}

classMan{privateBestFriend<dog>}

Question5Given:

Object[]myObjects={

newinteger(12),

newString(”foo”),

newinteger(5),

newBoolean(true)

};

Arrays.sort(myObjects);

for(inti=0;i<myObjects.length;i++){

System.out.print(myObjects[i].toString());

System.out.print(”“);

}

Whatistheresult?

Compilationfailsduetoanerrorinline23.

Compilationfailsduetoanerrorinline29.

AClassCastExceptionoccursinline29.

AClassCastExceptionoccursinline31.

Thevalueofallfourobjectsprintsinnaturalorder.

Question6

Given:

publicclassPass{

publicstaticvoidmain(String[]args){

intx=5;

Passp=newPass();

p.doStuff(x);

System.out.print(”mainx=“+x);

}

voiddoStuff(intx){

System.out.print(”doStuffx=“+x++);

}

}

Whatistheresult?

Compilationfails.

Anexceptionisthrownatruntime.

doStuffx=6mainx=6

doStuffx=5mainx=5

doStuffx=5mainx=6

doStuffx=6mainx=5

Question7Given:

classNav{

publicenumDirection{NORTH,SOUTH,EAST,WEST}

}

publicclassSprite{

//insertcodehere

}

Whichcode,insertedatline14,allowstheSpriteclasstocompile?

Directiond=NORTH;

Nav.Directiond=NORTH;

Directiond=Direction.NORTH;

Nav.Directiond=Nav.Direction.NORTH;

Question8Given:

publicstaticvoidparse(Stringstr){

try{

floatf=Float.parseFloat(str);

}catch(NumberFormatExceptionnfe){

f=0;

}finally{

System.out.println(f);

}

}

publicstaticvoidmain(String[]args){

parse(”invalid”);

}

Whatistheresult?

0.0

Compilationfails.

AParseExceptionisthrownbytheparsemethodatruntime.

ANumberFormatExceptionisthrownbytheparsemethodatruntime.

Question9

Aprogrammerneedstocreatealoggingmethodthatcanacceptanarbitrarynumberofarguments.Forexample,itmaybecalledinthese

ways:

logIt(”logmessage1“);

logIt(”logmessage2”,”logmessage3”);

logIt(”logmessage4”,“logmessage5”,“logmessage6);Whichdeclarationsatisfiesthisrequirement?

publicvoidlogIt(String*msgs)

publicvoidlogIt(String[]msgs)

publicvoidlogIt(String...msgs)

publicvoidlogIt(Stringmsg1,Stringmsg2,Stringmsg3)

Question10

ClicktheExhibitbutton.

1.publicclassA{2.

3.privateintcounter=0;

4.

publicstaticintgetInstanceCount(){

returncounter;

}

publicA(){

counter++;

}

}

GiventhiscodefromClassB:

Aa1=newA();

Aa2=newA();

Aa3=newA();

System.out.printIn(A.getInstanceCount());Whatistheresult?

CompilationofclassAfails.

Line28printsthevalue3toSystem.out.

Line28printsthevalue1toSystem.out.

Aruntimeerroroccurswhenline25executes.

Compilationfailsbecauseofanerroronline28.

Question11Given:

publicstaticvoidmain(String[]args){

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

if(i>6)break;

}

System.out.println(i);

}

Whatistheresult?

6

7

10

11

Compilationfails.

Anexceptionisthrownatruntime.

Question12

Given:

publicstaticvoidsearch(List<String>list){

list.clear();

list.add(”b”);

list.add(”a”);

list.add(”c”);

System.out.println(Collections.binarySearch(list,“a”));

}

WhatistheresultofcallingsearchwithavalidListimplementation?

0

1

2

a

b

c

Theresultisundefined.

Question13

ClicktheExhibitbutton.

classFoo{

privateintx;

publicFoo(intx){this.x=x;}

publicvoidsetX(intx){this.x=x;}

publicintgetX(){returnx;}

}

publicclassG{18.

staticFoofooBar(Foofoo){

foo=newFoo(100);

returnfoo;

}

publicstaticvoidmain(String[]args){

Foofoo=newFoo(300);

System.out.print(foo.getX()+“-“);27.

FoofooFoo=fooBar(foo);

System.out.print(foo.getX()+“-“);

System.out.print(fooFoo.getX()+“-“);31.

foo=fooBar(fooFoo);

System.out.print(foo.getX()+“-“);

System.out.prmt(fooFoo.getX());

}

}

Whatistheoutputofthisprogram?

300-100-100-100-100

300-300-100-100-100

300-300-300-100-100

300-300-300-300-100

Question14

Given:

publicvoidgenNumbers(){

ArrayListnumbers=newArrayList();

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

intvalue=i*((int)Math.random());

IntegerintObj=newInteger(value);

numbers.add(intObj);

}

System.out.println(numbers);

}

WhichlineofcodemarkstheearliestpointthatanobjectreferencedbyintObj esacandidateforgarbagecollection?

Line16

Line17

Line18

Line19

TheobjectisNOTacandidateforgarbagecollection.

Question15Given:

publicclassThreads3implementsRunnable{

publicvoidrun(){

System.out.print(”running”);

}

publicstaticvoidmain(String[]args){

Threadt=newThread(newThreads3());

t.run();

t.run();

t.start();

10.}

11.}

Whatistheresult?

Compilationfails.

Anexceptionisthrownatruntime.

Thecodeexecutesandprints“running”.

Thecodeexecutesandprints“runningrunning”.

Thecodeexecutesandprints“runningrunningrunning”.

編程題：

請完成下列程序中的insert()函數，完成雙向鏈表的建立，并使得鏈表中的元素從小到大有序排列。

publicclassTestDuLink{

publicstaticvoidmain(Stringargs[]){

DuLinkl=newDuLink();l.insert("4");

l.insert("6");

l.insert("5");

l.insert("1");

l.insert("2");

l.insert