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java

question1）

whatwillhappenwhenyouattempttocompileandrunthiscode?

abstractclassbase{

abstractpublicvoidmyfunc（）;

publicvoidanother（）{

system.out.println（"anothermethod"）;

}

}

publicclassabsextendsbase{

publicstaticvoidmain（stringargv[]）{

absa=newabs（）;

a.amethod（）;

}

publicvoidmyfunc（）{

system.out.println（"myfunc"）;

}

publicvoidamethod（）{

myfunc（）;

}

}

1）thecodewillcompileandrun,printingoutthewords"myfunc"

2）thecompilerwillcomplainthatthebaseclasshasnonabstractmethods

3）thecodewillcompilebutcomplainatruntimethatthebaseclasshasnonabstractmethods

4）thecompilerwillcomplainthatthemethodmyfuncinthebaseclasshasnobody,nobodyatalltoloooveit

question2）

whatwillhappenwhenyouattempttocompileandrunthiscode?

publicclassmymain{

publicstaticvoidmain（Stringargv）{//改为：

main（String[]argv）

System.out.println（"hellocruelworld"）;

}

}

1）thecompilerwillcomplainthatmainisareservedwordandcannotbeusedforaclass

2）thecodewillcompileandwhenrunwillprintout"hellocruelworld"

3）thecodewillcompilebutwillcomplainatruntimethatnoconstructorisdefined

4）thecodewillcompilebutwillcomplainatruntimethatmainisnotcorrectlydefined

question5）（不做）

whymightyoudefineamethodasnative?

1）togettoaccesshardwarethatjavadoesnotknowabout

2）todefineanewdatatypesuchasanunsignedinteger

3）towriteoptimisedcodeforperformanceinalanguagesuchasc/c++

4）toovercomethelimitationoftheprivatescopeofamethod

question6）

whatwillhappenwhenyouattempttocompileandrunthiscode?

classbase{

publicfinalvoidamethod（）{

System.out.println（"amethod"）;

}

}

publicclassfinextendsbase{

publicstaticvoidmain（Stringargv[]）{

baseb=newbase（）;

b.amethod（）;

}

}

1）compiletimeerrorindicatingthataclasswithanyfinalmethodsmustbedeclaredfinalitself

2）compiletimeerrorindicatingthatyoucannotinherit（继承）fromaclasswithfinalmethods

3）runtimeerrorindicatingthatbaseisnotdefinedasfinal

4）successincompilationandoutputof"amethod"atruntime

question7）（不做）

whatwillhappenwhenyouattempttocompileandrunthiscode?

publicclassmod{

publicstaticvoidmain（Stringargv[]）{

}

publicstaticnativevoidamethod（）;

}

1）erroratcompilation:

nativemethodcannotbestatic

2）erroratcompilationnativemethodmustreturnvalue

3）compilationbuterroratruntimeunlessyouhavemadecodecontainingnativeamethodavailable

4）compilationandexecutionwithouterror

question8）

whatwillhappenwhenyouattempttocompileandrunthiscode?

privateclassbase{}//类的修饰符只能是public,final,abstract

publicclassvis{

transientintival;

publicstaticvoidmain（Stringelephant[]）{

}

}

1）compiletimeerror:

basecannotbeprivate

2）compiletimeerrorindicatingthatanintegercannotbetransient

3）compiletimeerrortransientnotadatatype

4）compiletimeerrormalformedmainmethod

question9）

whathappenswhenyouattempttocompileandrunthesetwofilesinthesamedirectory?

//filep1.java

packagemypackage;

classp1{

voidafancymethod（）{

system.out.println（"whatafancymethod"）;

}

}

//filep2.java

publicclassp2extendsp1{

publicstaticvoidmain（Stringargv[]）{

p2p2=newp2（）;

p2.afancymethod（）;

}

}

1）bothcompileandp2outputs"whatafancymethod"whenrun

2）neitherwillcompile

3）bothcompilebutp2hasanerroratruntime

4）p1compilescleanlybutp2hasanerroratcompiletime

question10）

youwanttofindoutthevalueofthelastelementofanarray.youwritethefollowingcode.whatwillhappenwhenyoucompileandrunit.?

publicclassmyar{

publicstaticvoidmain（Stringargv[]）{

int[]i=newint[5];

System.out.println（i[5]）;//数组越界

}

}

1）anerroratcompiletime

2）anerroratruntime

3）thevalue0willbeoutput

4）thestring"null"willbeoutput

question18）

whatwillhappenwhenyouattempttocompileandrunthefollowingcode?

publicclassbgroundextendsthread{

publicstaticvoidmain（stringargv[]）{

bgroundb=newbground（）;

b.run（）;//应该是重写run（）方法，继承start（）方法，

}

publicvoidstart（）{

for（inti=0;i<10;i++）{

system.out.println（"valueofi="+i）;

}

}

}

1）acompiletimeerrorindicatingthatnorunmethodisdefinedforthethreadclass

2）aruntimeerrorindicatingthatnorunmethodisdefinedforthethreadclass

3）cleancompileandatruntimethevalues0to9areprintedout

4）cleancompilebutnooutputatruntime

question25）

whatwillhappenwhenyouattempttocompileandrunthefollowingcode

publicclasshope{

publicstaticvoidmain（Stringargv[]）{

hopeh=newhope（）;

}

protectedhope（）{

for（inti=0;i<10;i++）{

System.out.println（i）;

}

}

}

1）compilationerror:

constructorscannotbedeclaredprotected

2）runtimeerror:

constructorscannotbedeclaredprotected

3）compilationandrunningwithoutput0to10

4）compilationandrunningwithoutput0to9

question26）

whatwillhappenwhenyouattempttocompileandrunthefollowingcode

publicclassmyswitch{

publicstaticvoidmain（Stringargv[]）{

myswitchms=newmyswitch（）;

ms.amethod（）;

}

publicvoidamethod（）{

intk=10;

switch（k）{

case10:

system.out.println（"ten"）;

case20:

system.out.println（"twenty"）;

break;

default:

system.out.println（"thisisthedefaultoutput"）;

break;

}

}

}

1）noneoftheseoptions//应该是tentwenty

2）compiletimeerrortargetofswitchmustbeanintegraltype

3）compileandrunwithoutput"thisisthedefaultoutput"

4）compileandrunwithoutputofthesingleline"ten"

question28）

whatwillhappenwhenyouattempttocompileandrunthefollowingcode

publicclassas{

inti=10;

intj;

charz=1;

booleanb;

publicstaticvoidmain（Stringargv[]）{

asa=newas（）;

a.amethod（）;

}

publicvoidamethod（）{

System.out.println（j）;

System.out.println（b）;

}

}

1）compilationsucceedsandatruntimeanoutputof0andfalse

2）compilationsucceedsandatruntimeanoutputof0andtrue

3）compiletimeerrorbisnotinitialised

4）compiletimeerrorzmustbeassignedacharvalue

question29）

whatwillhappenwhenyouattempttocompileandrunthefollowingcodewiththecommandline"hellothere"

publicclassarg{

string[]myarg;

publicstaticvoidmain（stringargv[]）{

myarg=argv;//静态方法只能使用静态变量，myarg不是静态变量

}

publicvoidamethod（）{

System.out.println（argv[1]）;//argv是局部变量，在这个函数里不能使用

}

}

1）compiletimeerror

2）compilationandoutputof"hello"

3）compilationandoutputof"there"

4）noneoftheabove

question30）

whatwillhappenwhenyouattempttocompileandrunthefollowingcode

publicclassstreq{

publicstaticvoidmain（stringargv[]）{

streqs=newstreq（）;

}

privatestreq（）{

strings="marcus";

strings2=newstring（"marcus"）;

if（s==s2）{

system.out.println（"wehaveamatch"）;

}else{

system.out.println（"notequal"）;

}

}

}

1）compiletimeerrorcausedbyprivateconstructor

2）outputof"wehaveamatch"

3）outputof"notequal"

4）compiletimeerrorbyattemptingtocomparestringsusing==

question31）

whatwillhappenwhenyouattempttocompileandrunthefollowingcode

importjava.io.*;

classbase{

publicvoidamethod（）throwsfilenotfoundexception{}

}

publicclassexcepdemoextendsbase{

publicstaticvoidmain（stringargv[]）{

excepdemoe=newexcepdemo（）;

}

publicvoidamethod（）{}//重写方法时，子类的方法抛出的异常只能比父类的少，不能比父类多

protectedexcepdemo（）{

try{

datainputstreamdin=newdatainputstream（system.in）;

system.out.println（"pausing"）;

din.readbyte（）;

system.out.println（"continuing"）;

this.amethod（）;

}catch（ioexceptionioe）{}

}

}

1）compiletimeerrorcausedbyprotectedconstructor

2）compiletimeerrorcausedbyamethodnotdeclaringexception

3）runtimeerrorcausedbyamethodnotdeclaringexception

4）compileandrunwithoutputof"pausing"and"continuing"afterakeyishit

question32）

whatwillhappenwhenyouattempttocompileandrunthisprogram

publicclassouter{

publicstringname="outer";

publicstaticvoidmain（stringargv[]）{

inneri=newinner（）;

i.showname（）;

}//endofmain

privateclassinner{

stringname=newstring（"inner"）;

voidshowname（）{

system.out.println（name）;

}

}//endofinnerclass

}

1）compileandrunwithoutputof"outer"

2）compileandrunwithoutputof"inner"

3）compiletimeerrorbecauseinnerisdeclaredasprivate

4）compiletimeerrorbecauseofthelinecreatingtheinstanceofinner

question33）（不做）

whatwillhappenwhenyouattempttocompileandrunthiscode

//demonstrationofeventhandling

importjava.awt.*;

importjava.awt.event.*;

publicclassmywcextendsframeimplementswindowlistener{

publicstaticvoidmain（stringargv[]）{

mywcmwc=newmywc（）;

}

publicvoidwindowclosing（windoweventwe）{

system.exit（0）;

}//endofwindowclosing

publicvoidmywc（）{

setsize（300,300）;

setvisible（true）;

}

}//endofclass

1）erroratcompiletime

2）visibleframecreatedthatthatcanbeclosed

3）compilationbutnooutputatruntime

4）erroratcompiletimebecauseofcommentbeforeimportstatements

question34）

whichoptionmostfullydescribeswillhappenwhenyouattempttocompileandrunthefollowingcode

publicclassmyar{

publicstaticvoidmain（stringargv[]）{

myarm=newmyar（）;

m.amethod（）;

}

publicvoidamethod（）{

staticinti;//局部变量不能定义为static，编译出错

system.out.println（i）;

}

}

1）compilationandoutputofthevalue0

2）compiletimeerrorbecauseihasnotbeeninitialized

3）compilationandoutputofnull

4）compiletime