测试与答案4.docx
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测试与答案4
J@Whiz1.4---30道1.4模拟经典题（附详解）
1.Whatwillhappenwhenyouattempttocompileandrunthefollowingcode?
（Assumethatthecodeiscompiledandrunwithassertionsenabled.）
publicclassAssertTest{
publicvoidmethodA（inti）{
asserti>=0:
methodB（）;/////此处要求表达式，返回值VOID，通不过编译。
System.out.println（i）;
}
publicvoidmethodB（）{ //无返回值
System.out.println（"Thevaluemustnotbenegative"）;
}
publicstaticvoidmain（Stringargs[]）{
AssertTesttest=newAssertTest（）;
test.methodA（-10）;
}
}
A.itwillprint-10
B.itwillresultinAssertionErrorshowingthemessage-“thevaluemustnotbenegative”.
C.thecodewillnotcompile.
D.Noneofthese.
2.Whatwillhappenwhenyouattempttocompileandrunthefollowingcode?
D
publicclassStatic{
static{
intx=5; //在static内有效
}
staticintx,y; //初始化为0
publicstaticvoidmain（Stringargs[]）{
x--; //-1
myMethod（）;
System.out.println（x+y+++x）;
}
publicstaticvoidmyMethod（）{
y=x+++++x; //y=-1+1 x=1
}
}
A.compiletimeerror
B.prints:
1
C.prints:
2
D.prints:
3
E.prints:
7
F.prints:
8
3.Giventhefollowingcode,whatwillbetheoutput?
B
classValue{
publicinti=15;
}
publicclassTest{
publicstaticvoidmain（Stringargv[]）{
Testt=newTest（）;
t.first（）;
}
publicvoidfirst（）{
inti=5;
Valuev=newValue（）;
v.i=25;
second（v,i）;
System.out.println（v.i）;
}
publicvoidsecond（Valuev,inti）{
i=0;
v.i=20;
Valueval=newValue（）;
v=val;
System.out.println（v.i+""+i）;
}
}
A.15020
B.15015
C.20020
D.01520
4.Whatwillhappenwhenyouattempttocompileandrunthefollowingcode?
classMyParent{
intx,y;
MyParent（intx,inty）{
this.x=x;
this.y=y;
}
publicintaddMe（intx,inty）{
returnthis.x+x+y+this.y;
}
publicintaddMe（MyParentmyPar）{
returnaddMe（myPar.x,myPar.y）;
}
}
classMyChildextendsMyParent{
intz;
MyChild（intx,inty,intz）{
super（x,y）;
this.z=z;
}
publicintaddMe（intx,inty,intz）{
returnthis.x+x+this.y+y+this.z+z;
}
publicintaddMe（MyChildmyChi）{
returnaddMe（myChi.x,myChi.y,myChi.z）;
}
publicintaddMe（intx,inty）{
returnthis.x+x+this.y+y;
}
}
publicclassMySomeOne{
publicstaticvoidmain（Stringargs[]）{
MyChildmyChi=newMyChild（10,20,30）;
MyParentmyPar=newMyParent（10,20）;
intx=myChi.addMe（10,20,30）;
inty=myChi.addMe（myChi）;
intz=myPar.addMe（myPar）;
System.out.println（x+y+z）;
}
}
A.300
B.240
C.120
D.180
E.compileerror
F.noneoftheabove
5.TheclassAssertionErrorhas"is-a"relationshipwiththeseclasses（choosetwo）B，E
A.RuntimeException
B.Error
C.VirtualMachineError
D.IllegalAccessException
E.Throwable
6.Whatwillbetheresultofexecutingthefollowingcode?
D
1.booleana=true;
2.booleanb=false;
3.booleanc=true;
4.if（a==true）
5. if（b==true）
6. if（c==true）System.out.println（"Somethingsaretrueinthisworld"）;
7. elseSystem.out.println（"Nothingistrueinthisworld!
"）;
8. elseif（a&&（b=c）） //这里是赋值，不是比较
System.out.println（"It'stooconfusingtotellwhatistrueandwhatisfalse"）;
9. else System.out.println（"Heythiswon'tcompile"）;
A.Thecodewon’tcompile.
B.“somethingsaretrueinthisworld”willbeprinted
C.“heythiswon’tcompile”willbeprinted
D.Noneofthese
7.Whatwillhappenwhenyouattempttocompileandrunthefollowingcode?
C
interfaceMyInterface{}
publicclassMyInstanceTestimplementsMyInterface{
staticStrings;
publicstaticvoidmain（Stringargs[]）{
MyInstanceTestt=newMyInstanceTest（）;
if（tinstanceofMyInterface）{
System.out.println（"Iamtrueinterface"）;
}else{
System.out.println（"Iamfalseinterface"）;
}
if（sinstanceofString）{
System.out.println（"IamtrueString"）;
}else{
System.out.println（"IamfalseString"）;
}
}
}
A.compiletimeerror
B.runtimeerror
C.prints:
“Iamtrueinterface”followedby“IamtrueString”
D.prints:
“Iamfalseinterface”followedby“IamfalseString”
E.prints:
“Iamtrueinterface”followedby“IamfalseString”
F.prints:
“Iamfalseinterface”followedby“IamtrueString”
8.Whatresultsfromattemptingtocompileandrunthefollowingcode?
D
publicclassTernary{
publicstaticvoidmain（Stringargs[]）{
inta=5;
System.out.println（"Valueis-"+（（a<5）?
9.9:
9））;
}
}
A.print:
Valueis-9
B.print:
Valueis-5
C.Compilationerror
D.Noneofthese
9.Inthefollowingpiecesofcode,AandDwillcompilewithoutanyerror.True/False?
FAL
A:
StringBuffersb1="abcd";
B:
Booleanb=newBoolean（"abcd"）;
C:
byteb=255;
D:
intx=0x1234;
E:
floatfl=1.2;
10.Consideringthefollowingcode,Whichvariablesmaybereferencedcorrectlyatline12?
ABCE
1.publicclassOuter
2.{
3.publicinta=1;
4.privateintb=2;
5.publicvoidmethod（finalintc）
6.{
7.intd=3;
8.classInner
9.{
10.privatevoidiMethod（inte）
11.{
12.
13.}
14.}
15.}
16.}
abcde
11.Whatwillbetheresultofexecutingthefollowingcode?
C
publicstaticvoidmain（Stringargs[]）{
chardigit='a';
for（inti=0;i<10;i++）{
switch（digit）{
case'x':
{
intj=0;
System.out.println（j）;
}
default:
{
intj=100;
System.out.println（j）;
}
}
}
inti=j;
System.out.println（i）;
}
A.100willbeprinted11times.
B.100willbeprinted10timesandthentherewillbearuntimeexception
C.Thecodewillnotcompilebecausethevariableicannotbedeclaredtwicewithinthemani（）method.
D.Thecodewillnotcompilebecausethevariablejcannotbedeclaredtwicewithintheswitchstatement.
E.Noneofthese.
12.Whichofthefollowingcollectionclassesfromjava.utilpackageareThreadsafe?
A
A.Vector
B.ArrayList //与Vector类似，只是不同步
C.HashMap
D.Hashtable
13.Whatwillhappenwhenyouattempttocompileandrunthefollowingcode?
CD
classMyThreadextendsThread{
publicvoidrun（）{
System.out.println（"MyThread:
run（）"）;
}
publicvoidstart（）{
System.out.println（"MyThread:
start（）"）;
}
}
classMyRunnableimplementsRunnable{
publicvoidrun（）{
System.out.println（"MyRunnable:
run（）"）;
}
publicvoidstart（）{
System.out.println（"MyRunnable:
start（）"）;
}
}
publicclassMyTest{
publicstaticvoidmain（Stringargs[]）{
MyThreadmyThread = newMyThread（）;
MyRunnablemyRunnable=newMyRunnable（）;
Threadthread = newThread（myRunnable）;
myThread.start（）;
thread.start（）;
}
}
A.prints:
MyThread:
start（）followedbyMyRunnable:
run（）
B.prints:
MyThread:
run（）followedbyMyRunnable:
start（）
C.prints:
MyThread:
start（）followedbyMyRunnable:
start（）
D.prints:
MyThread:
run（）followedbyMyRunnable:
run（）
E.compiletimeerror
F.Noneoftheabove
14.Whatwillbetheresultofexecutingthefollowingcode?
D
//Filename;SuperclassX.java
packagepackageX;
publicclassSuperclassX{
protectedvoidsuperclassMethodX（）{}
intsuperclassVarX;
}
//FilenameSubclassY.java
1.packagepackageX.packageY;
2.
3.publicclassSubclassYextendsSuperclassX
4.{
5.SuperclassXobjX=newSubclassY（）;
6.SubclassYobjY=newSubclassY（）;
7.voidsubclassMethodY（）
8.{
9.objY.superclassMethodX（）;
10.inti;
11.i=objY.superclassVarX;
12.}
13.}
A.Compileerroratline5.
B.Compileerroratline9.
C.Runtimeexceptionatline11.
D.Noneofthese
15.Considertheclasshierarchyshownbelow:
E
FourWheeler
（implementsDrivingUtilities）
//\\
/ / \ \
/ / \ \
/ / \ \
/ / \ \
Car Truck Bus Crane
Considerthefollowingcodebelow:
1.DrivingUtilitiesdu;
2.FourWheelerfw;
3.TruckmyTruck=newTruck（）;
4.du=（DrivingUtilities）myTruck;
5.fw=newCrane（）;
6.fw=du;
Whichofthestatementsbelowaretrue?
A.Line4willnotcompilebecauseaninterfacecannotrefertoanobject.
B.Thecodewillcompileandrun.
C.Thecodewillnotcompilewithoutanexplicitcastatline6,becausegoingdownthehierarchywithoutcastingisnotallowed.
D.Thecodeatline4willcompileevenwithouttheexplicitcast.
E.Thecodewillcompileifweputanexplicitcastatline6butwillthrowanexceptionatruntime.
16.Whatresultsfromthefollowingcode?
D
1.classMyClass
2.{
3.voidmyMethod（inti）{System.out.println（"intversion"）;}
4.voidmyMethod（Strings）{System.out.println（"Stringversion"）;}
5.publicstaticvoidmain（Stringargs[]）
6.{
7.MyClassobj=newMyClass（）;
8.charch='c';
9.obj.myMethod（ch）;
10.}
11.}
A.Line4willnotcompileasvoidmethodcan’teoverridden.
B.Anexceptionatline9.
C.Line9willnotcompileasthereisnoversionofmyMethodwhichtakesacharasargument.
D.Thecodecompilesandproducesoutput:
intversion
E.Thecodecompilesandproducesoutput:
Stringversion
17.Whatistheresultwhenyoucompileandrunthefollowingcode?
D
publicclassThrowsDemo{
staticvoidthrowMethod（）{
System.out.println（"InsidethrowMethod."）;
thrownewIllegalAccessException（"demo"）;
}
publicstaticvoidmain（Stringargs[]）{
try{
throwMethod（）;
}catch（IllegalAccessExceptione）{
System.out.println（"Caught"+e）;
}
}
}
A.compileerror
B.runtimeerror
C.compilesuccessfully,nothingisprinted.
D.insidethrowMethodfollowedbycaught:
java.lang.IllegalAccessException:
demo
18.Whatwillbeprintedwhenyouexecutethefollowingcode?
C
classX{
Yb=newY（）;
X（）{
System.out.print（"X"）;
}
}
classY{
Y（）{
System.out.print（"Y"）;
}
}
publicclassZextendsX{
Yy=newY（）;
Z（）{
System.out.print（"Z"）;
}
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