java认证 习题 第04章 有答案版 OK该试题还有第0305章.docx
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java认证 习题 第04章 有答案版 OK该试题还有第0305章.docx
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java认证习题第04章有答案版OK该试题还有第0305章
1、whatistheresultwhenyoucompileandrunthefollowingcode?
C
ClassExample
{
Publicstaticvoidmain(String[]args)
{
System.out.println(3/0);
}
}
Selectallrightanswer:
Aacompilererror
Baruntimeerror
Cjava.lang.ArtithmeticException:
/byzero
Dinfinity
考察算术运算,分母为0,非法
2、whichresultsistruewhenyoucompileandrunthefollowingcode?
B
booleanb1=true;Booleanb2=false
Selectallrightanswer:
A、b1==b2B、b1||b2C、b1|&b2D、b1&&b2
考察逻辑运算,A返回false,C语法错误运算符没有连接操作,D返回false
3、whatistheresultwhenyoucompileandrunthefollowingcode?
C
ClassExample
{
Publicstaticvoidmain(String[]args)
{
inti=1;
intj;
j=i++;
System.out.print(i+”,”+j);
}
}
Selectallrightanswer:
A、1,1B。
1,2C、2,1D、2,2
运算过程是:
先把i赋给j,此时i=1,y=1,然后i自动加1,并把结果赋给I,则i变为2
4、whatistheresultwhenyoucompileandrunthefollowingcode?
A
ClassExample
{
Publicstaticvoidmain(String[]args)
{
intx=5;
booleany=true;
System.out.print(x } } 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
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