计算机科学与技术外文翻译.docx

计算机科学与技术外文翻译.docx

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计算机科学与技术外文翻译

毕业设计（论文）外文资料

原文及译文

专业计算机科学与技术

班级08104121

学号0810411504

姓名

指导教师

原文出处：

Flash8ActionScriptBible,JoeyLottandRobertReinhardt,PublishedbyWileyPublishing,Inc.

Flash8ActionScriptBible

JoeyLottandRobertReinhardt

UnderstandingDatatypes

Whenwetalkaboutdata,we’retalkingaboutinformationorvalues.Thesevaluescanbeofmanytypes.Forexample,eveninaverysimplemovieyoumightstillhaveanumber,sometext,andaMovieClipinstance.Allthreeoftheseexamplesaredataofdifferenttypes—whatActionScriptcallsdatatypes.

Flashisactuallycapableofperformingdatatypeconversionswhennecessary.However,thiscanleadtosomepoorcodingpracticesonthepartofActionScriptdevelopers.Forthisreason,theActionScript2.0standardsrequirethatyoupaycloserattentiontothedatatypesyouareusing.

InActionScript,you’llworkwithmanydifferentdatatypes.However,forthesakeofunderstandinghowthesedatatypeswork,youcanconsiderthemintwobasiccategories:

primitivetypesandreferencetypes.Theprimitivetypesarecalledprimitivebecausetheyarethebasicfoundationaldatatypes,notbecausetheylackimportance.Thereferencedatatypesarecalledreferencetypesbecausetheyreferencetheprimitivetypes.

Primitivedatatypesincludestrings,numbers,Booleans,undefined,andnull.We’llexamineeachoftheseprimitivedatatypesalittlemorecloselyinthischapter.Referencedatatypesareallobjects,whichisthesubjectofmuchoftherestofthisbook,sowe’lldeferthemajorityofthediscussionofreferencedatatypestothoselaterchapters.

WorkingwithStrings

Stringsarecharactersorwords.Stringvaluesmustalwaysbeenclosedineithersinglequotesordoublequotes.Hereareafewexamplesofstrings:

“a”

‘b’

“1”

“Joey”

‘123’

‘abc’

“****”

Stringsareusedwheneveryouwanttoworkwithcharactersorwords.Forexample,youcanusestringstopopulatetextfieldsinyourmovie,oryoucanusestringstoprogrammaticallycreatenamesfornewMovieClipinstances.You’vealsoalreadyseenhowstringscanbeusedwithactionssuchastrace（）.Thetrace（）actionrequiresthatyouprovideitwithamessagetodisplayintheOutputpanel.Thatmessagemustevaluatetoastringvalue.

trace（“Iknowhim;Marley’sGhost!

”）;

Asalreadymentioned,youcanuseeitherdoublequotesorsinglequoteswhendefiningastringvalue.Whichyouchooseisoftenpurelyamatterofpersonalpreference.Therearetworulesthatyoumustfollow,however,ifyouwantyourcodetoworkwithouterror.First,youmusthaveamatchingclosingquoteforeveryopeningquote.Andwhichevertypeofquoteyouusetoopenthestringliteralmustbeusedtocloseit.Inotherwords,mismatchedquotesarenotallowed.Herearetwoexamplesofcorrectlymatchedquotesonstringliterals:

“hereisastring”

‘hereisastring’

Andherearethreeexamplesofincorrectquotesonstringliterals:

“hereisastring’

‘hereisastring”

“hereisastring

Therearetimeswhenmorethanpersonalpreferencemightdictatewhichtypeofquotesyouchoosetouse.Noticewhatwouldhappenifyoutriedthefollowing:

trace（‘Iknowhim;Marley’sGhost!

’）;

Thislineofcodewouldactuallycauseanerrorbecauseitwouldinterprettheapostropheastheclosingquoteandthenfailtoknowwhattodowiththeremainderofthestring.Thisiseasilyremediedbyusingdoublequotesaroundthestring:

trace（“Iknowhim;Marley’sGhost!

”）;

Theinverseistrueaswell,ofcourse—ifyouwanttouseadoublequotationmarkasacharacterinastringliteral,youcanusesinglequotesaroundtheentirevalue.Theproblemariseswhenyouwanttousebothsingleanddoublequotationmarksascharacterswithinastringliteral.Thereisaneasywaytoaccommodatethis:

byusingspecialcharacters.Tolearnmoreaboutspecialcharacters,seeChapter11.

WorkingwithNumbers

InFlash,allnumbersaretreatedasthenumberdatatype.Positive,negative,floatingpoint,integer,andsoforth,areallsimplyconsiderednumbers,withnofurtherdifferentiationgenerallyrequiredonyourpart.

Todefineanumber,youneedonlytypethenumberwithoutanyquotes.Thefollowingareexamplesofnumbers.

6

12

-1

3.3

1.8

Numberdatatypesallowyoutoperformallkindsofmathematicaloperations,asshowninthefollowingexamples:

trace（5+5）;//Displays:

10

trace（5–4）;//Displays:

1

trace（5/2）;//Displays:

2.5

Itisimportanttounderstandwhentousenumbersandwhentousestrings.Ifyoutrytouseastringwhenyoureallywanttouseanumber,youcanendupwithunexpectedresults.Forexample:

trace（“5”+“5”）;//Displays:

55

Intheexample,theresultingvalueofaddedAgesis“55”,not10（asyoumayexpect）.ThisisbecauseActionScripttreatsthetwovaluesasstringsandconcatenatesthem,ratherthanaddin