}
}
Selectallrightanswer:
A、acompilererror
B、arunningerror
C、true
D、false
考察关系运算，不能用0替代false
5、whatistheresultwhenyoucompileandrunthefollowingcode?
A
ClassExample
{
Publicstaticvoidmain（String[]args）
{
Shorts=newShort（“5”）;
Booleanb;
//insertcodehere
}
}
Which,insertedindependentlyat//insertcodehere?
willcompile?
BD
Selectallrightanswer:
Ab=（Numberinstanceofs）;
Bb=（sinstanceofShort）;
Cb=sinstanceof（Short）;
Db=（sinstanceofNumber）;
Eb=sinstanceof（Object）;
Fb=（sinstanceofString）;
考察instanceof运算符，A写反了，C.E语法错误F类型不兼容
6、whichofthefollowinglinesofcodewillcompilewithouterror?
BC
A
inti=0;
if（i）System.out.println（“Hi”）;
B
booleanb=true;
booleanb2=true;
if（b==b2）System.out.println（“sotrue”）;
C
inti=1;
intj=2;
if（i==1||j==2）System.out.println（“OK”）;
D
inti=1;
intj=2;
if（i==1&|j==2）System.out.println（“OK”）;
本题考察boolean表达式，A错在不能用数字充当boolean型值，D错在逻辑操作非法
7、whatistheresultwhenyoucompileandrunthefollowingcode?
BD
ClassExample
{
Publicstaticvoidmain（String[]args）
{
Floatf=newFloat（4.2f）;
Floatc;
Doubled=newDouble（4.2）;
floatf1=4.2f;
c=f;
}
}
Selectallrightanswer:
Af.equals（d）Bc==fCc==dDc.equals（f）
＝＝比较内存地址，equals比较内容
8、whatistheresultwhenyoucompileandrunthefollowingcode?
D
ClassExample
{
Publicstaticvoidmain（String[]args）
{
bytex=-－64;
bytey=-－6;
System.out.println（x/y+””+x%y）;
}
}
Selectallrightanswer:
AacompilererrorBaruntimeerrorC104D10－4
9、whatistheresultwhenyoucompileandrunthefollowingcode?
G
ClassExample
{
publicstaticvoidmain（String[]args）
{
longx=42L;
longx=44L;
System.out.println（““+7+2+”“）;
System.out.println（foo（）+x+5+”“）;
System.out.println（x+y+foo（））;
}
staticStringfoo（）
{return“foo”;
}
}
Selectallrightanswer:
A、9foo4786fooB、9foo474244fooC、9foo42586foo
D、9foo4254244fooE、72foo4786fooF、72foo474244foo
G、72foo42586fooH、72foo4254244fooI、compilationfails
本题考察字符串连接，，两个操作数中有一个以上字符串就进行连接，俩操作数都是数值时做＋运算
10、whatistheresultwhenyoucompileandrunthefollowingcode?
A
ClassExample
{
publicstaticvoidmain（String[]args）
{
Strings1=”Amit”;
Strings2=”Amit”;
Strings3=newString（“abcd”）;
Strings4=newString（“abcd”）;
System.out.println（s1.equals（s2））;
System.out.println（（s1==s2））;
System.out.println（s3.equals（s4））;
Strings3=newString（（s3==s4））;
}
}
Selectallrightanswer:
AtruetruetruefalseBtruetruetruetrueCtruefalsetruefalse
S1和S2内容一样，引用也一样，因为不是new的就都是从字符串池中取的，s3,s4内容一样，但不是指同一对象
11、whatistheresultwhenyoucompileandrunthefollowingcode?
B
charc=’c’;
inti=10;
doubled=10;
longl=1;
Strings=”Hello”
Selectallrightanswer:
Ac=c+iBs+=iCi+=sDc+s
＋＝符号左侧应是字符串
12、whichofthefollowingreturnstruewhenreplacewith*****?
A
ClassExample
{
publicstaticvoidmain（String[]args）
{
Buttonb=newButton（“Button”）;
if（*******）
System.out.println（“thisisaninstanceofButton”）;
}
}
Selectallrightanswer:
A、binstanceofButtonB、ButtoninstancofbC、b==ButtonD、Button==（Object）b
考察比较运算符，
13、whatistheresultwhenyoucompileandrunthefollowingcode?
A
importjava.awt.*;
ClassExample
{
publicstaticvoidmain（String[]args）
{
try
{
Button[]var=newButton[5];
System.out.println（varinstanceof[]）;
}
catch（Exceptione）
{
System.out.println（“Exceptionthrown”）;
}
}
}
Selectallrightanswer:
AacompilererrorBExceptionthrownCtrueDflaseEnoneoftheabove
Instanceof右侧应该是类，接口或数组类型
14、whatistheresultwhenyoucompileandrunthefollowingcode?
D132
importjava.awt.*;
ClassExample
{
publicstaticvoidmain（String[]args）
{
intOutput=10;
booleanb1=false;
if（（b1==true）&&（Output+=10）==20））
{
System.out.println（“weareequal”+Output）;
}
else
System.out.println（“Notequal”+Output）;
}
}
Selectallrightanswer:
Acompileerror,attemptingtoperformbinarycomparisononlogicaldatatype
BCompilationandoutputof“weareequal10”
Ccompilationandoutputof“notequal20”
Dcompilationandoutputof“notequal10”
考察逻辑短路因为逻辑短路，所以（Output+=1没被执行
15、whatistheresultwhenyoucompileandrunthefollowingcode?
F145
ClassExample
{Strings;
publicstaticvoidmain（String[]args）
{Exampleks=newExample（）;
intj,i;
i=ks.hai（）;
j=ks.hello（）;
System.out.println（i+””+j）;
}
inthai（）
{
if（（s==null）||（s.length（）==0））{return10;}
elsereturn0;
}
inthello（）
{
if（（s==null）||（s.length（）==20））{return10;}
elsereturn0;
}
}
Selectallrightanswer:
A1010B10nullC00DcompilationerrorEAnexceptioninhaiFanexceptoninhello
考察逻辑短路，|不属于短路运算，所以s.lengh（）会被执行，因为s为null，所以抛出异常
课后作业:
1.Given:
classHexy{
publicstaticvoidmain（String[]args）{
Integeri=42;
Strings=（i<40）?
"life":
（i>50）?
"universe":
"everything";
System.out.println（s）;
}
}
Whatistheresult?
A.null
B.life
C.universe
D.everything
E.Compilationfails.
F.Anexceptionisthrownatruntime.
Answer:
®3Discorrect.Thisisaternarynestedinaternarywithalittleunboxingthrownin.
Bothoftheternaryexpressionsarefalse.
®˚A,B,C,E,andFareincorrectbasedontheabove.
（Objective7.6）
2.Given:
1.classExample{
2.publicstaticvoidmain（String[]args）{
3.Shorts=15;
4.Booleanb;
5.//insertcodehere
6.}
7.}
Which,insertedindependentlyatline5,willcompile?
（Chooseallthatapply.）
A.b=（Numberinstanceofs）;
B.b=（sinstanceofShort）;
SelfTestAnswers307
C.b=s.instanceof（Short）;
D.b=（sinstanceofNumber）;
E.b=s.instanceof（Object）;
F.b=（sinstanceofString）;
Answer:
®3BandDcorrectlyuseboxingandinstanceoftogether.
®˚Aisincorrectbecausetheoperandsarereversed.CandEuseincorrectinstanceofsyntax.
FiswrongbecauseShortisn'tinthesameinheritancetreeasString.
（Objective7.6）
3.Given:
1.classComp2{
2.publicstaticvoidmain（String[]args）{
3.floatf1=2.3f;
4.float[][]f2={{42.0f},{1.7f,2.3f},{2.6f,2.7f}};
5.float[]f3={2.7f};
6.Longx=42L;
7.//insertcodehere
8.System.out.println（"true"）;
9.}
10.}
Andthefollowingfivecodefragments:
F1.if（f1==f2）
F2.if（f1==f2[2][1]）
F3.if（x==f2[0][0]）
F4.if（f1==f2[1,1]）
F5.if（f3==f2[2]）
Whatistrue?
A.Oneofthemwillcompile,onlyonewillbetrue.
B.Twoofthemwillcompile,onlyonewillbetrue.
C.Twoofthemwillcompile,twowillbetrue.
D.Threeofthemwillcompile,onlyonewillbetrue.
E.Threeofthemwillcompile,exactlytwowillbetrue.
F.Threeofthemwillcompile,exactlythreewillbetrue.
308Chapter4:
Operators
Answer:
®3Discorrect.FragmentsF2,F3,andF5willcompile,andonlyF3istrue.
®˚A,B,C,E,andFareincorrect.F1isincorrectbecauseyoucan’tcompareaprimitiveto
anarray.F4isincorrectsyntaxtoaccessanelementofatwo-dimensionalarray.
（Objective7.6）
4.Given:
classFork{
publicstaticvoidmain（String[]args）{
if（args.length==1|args[1].equals（"test"））{
System.out.println（"testcase"）;
}else{
System.out.println（"production"+args[0]）;
}
}
}
Andthecommand-lineinvocation:
javaForklive2
Whatistheresult?
A.testcase
B.production
C.testcaselive2
D.Compilationfails.
E.Anexceptionisthrownatruntime.
Answer:
®3Eiscorrect.Becausetheshortcircuit（||）isnotused,bothoperandsareevaluated.Since
args[1]ispasttheargsarraybounds,anArrayIndexOutOfBoundsExceptionisthrown.
®˚A,B,C,andDareincorrectbasedontheabove.
（Objective7.6）
SelfTestAnswers309
5.Given:
classFoozit{
publicstaticvoidmain（String[]args）{
Integerx=0;
Integery=0;
for（Shortz=0;z<5;z++）
if（（++x>2）||（++y>2））
x++;
System.out.println（x+""+y）;
}
}
Whatistheresult?
A.51
B.52
C.53
D.81
E.82
F.83
G.102
H.103
Answer:
®3Eiscorrect.Thefirsttwotimestheiftestruns,bothxandyareincrementedonce（the
x++isnotreacheduntilthethirditeration）.Startingwiththethirditerationoftheloop,
yisnevertouchedagain,becauseoftheshort-circuitoperator.
®˚A,B,C,D,F,G,andHareincorrectbasedontheabove.
（Objective7.6）
6.Given:
classTitanic{
publicstaticvoidmain（String[]args）{
Booleanb1=true;
booleanb2=false;
booleanb3=true;
if（（b1&b2）|（b2&b3）&b3）
System.out.print（"alpha"）;
if（（b1=false）|（b1&b3）|（b1|b2））
System.out.print（"beta"）;
}
}
310Chapter4:
Operators
Whatistheresult?
A.beta
B.alpha
C.alphabeta
D.Compilation
升级会员 