Programming MethodologyLecture26Word格式文档下载.docx

Programming MethodologyLecture26Word格式文档下载.docx

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vethought.Therecouldbeacouplepeoplewhoareathome,evenifyoudon'

twinofgetting100onthefinalinarandomdrawing.Sothat'

sagoodsign.

OnethingIdowanttocheck,Ijustheardalittlebitbeforeclassthatsomefolkswerehavingsometroublesubmittingtheirgraphicscontestbecausethereactuallymighthavebeenanissuewiththeserverthattakessubmissions.Soifyousubmittedtothegraphicscontest,whetheryou'

reinhereoryouhappentobewatchingthevideo,emailme,andletmeknowwhatthenameofyourcontestentrywas.Thatway,Iknowforsurethatweactuallygotallthecontestentriesthatwethinkwehad,andifwedidn'

tgetone,Icanemailyouback.ThethingIwouldaskyouis,ifyoucan'

temailmeanytimethisweekendbecausethisweekendisactually,whenwe'

regoingtomakethefirstpasslookingoverallthecontestentries,andthenwe'

regoingtohaveasmallpoolthatwe'

lltaketothesectionleaders.Theywillvoteandgivethewinner.I'

llannouncethewinnerinclassnextweek.

Imightshowademoofthewinningtwoaswell.Wemightdotherandomdrawinginclassaswelltoseewhoactuallygetsthethirdcovetedrandomdrawingspot,evenifyoudon'

twin.Sopleaseemailmeifyouenteredthegraphicscontest,justtomakesure.

OneotherthingwithemailforSCPDstudents,Iknowit'

sstillalittletooearlytothinkaboutfinalexams,butifyou'

reanSCPDstudent,it'

snottooearly.Ifyou'

renotanSCPDstudent,it'

snottooearly,either.ButforSCPDstudents,ifyou'

retakingthefinalexam,ifyouplanoftakingitatyoursitesandyou'

renotgoingtocomeoncampustotakeit,emailmeby5:

00p.m.December5,lettingmeknowthatyou'

retakingitatyoursiteandthenameandemailofyoursitecoordinator,justlikethemidterm.Thatway,Icangettheinformationtoyoursitecoordinatorforthefinalwellbeforethefinal.

Ifyou'

replanningoncomingoncampustotakethefinal,youcanfeelfreetosendmeanemailtosayyou'

recomingoncampus.IfIdon'

thearfromyou,Iwillassumeyou'

recomingoncampus.Soyouonlyneedtoemailmeifyou'

retakingitatyoursite,sopleasedothatifyou'

reanSCPDstudentandyouplanontakingitatyoursite.

Anyquestionsaboutanythingwe'

vedonesofarbeforewediveintoournextgreattopic?

Allright.

Oneofthethingsthatwe'

vedonethewholetimeinthisclassisweusethesethingscalledtheACMlibraries.TheACMlibrariesareasetoflibrariesthatareactuallycreatedbyataskforceofpeople.TheACMistheAssociationofComputingMachinery.Wetalkedaboutthemattheverybeginningoftheclasswhenwetalkedabouttheselibraries.Theyputtogethersomenicelibrariesofstuffthatarereallyusefulforteaching,whichiswhyweusethem.

Today,whatI'

mgoingtodoisliftalittlebitunderneaththehoodandtalkaboutstandardJava,whichiswhatyouwouldgetifyoudidn'

tusetheACMlibrariesandyoujustusedthestandardJavalibraries.Now,there'

snoreasonwhyyoucan'

tcontinuetousetheACMlibrariesafterthisclass.They'

rejustanothersetoflibrariesthatwerewrittenbyagroupofpeoplethatyou'

recertainlywelcometouse.

Sothere'

snoreasonwhyyoushouldstopusingthem,buttherewereacoupleimportantissuesrelatedtostandardJava.Nowit'

stimeforyoutoknow.Sothefirstthingthat'

srelatedtothinkingaboutstandardJavaiswhenyou'

rerunningyourprograms,whenyougointoEclipseandyouclickonthelittlerunningguytocompileyourprograms.Itgiveyoualistofwhatclassesyouactuallymightwanttorun.

Ifyouonlyhaveoneproject,youmayonlygetonechoice,butoneofthethingsyoukindofthinkaboutisinthenamesurferprogram,Iactuallyhavefourorfivedifferentclasses.Howcomeitalwaysknewwhichclasstorun?

HowcomeitalwaysknewthenamesurferclasswastheclassthatIactuallyshouldrun?

Anyonewanttoventureaguess?

Student:

[Inaudible].

It'

stheonlyclasswith[inaudible]whichisveryrelatedtoanunderlyingissue.It'

stheonlyclassthatactuallywasextendingprograms.Sooneoftheextendedprograms,whatactuallywashappeningintheseACMlibrariesisyouweregettingamethodcalledmain.Mainisactuallytheplace?

you'

reoldenoughtoseemain.MainisactuallythemethodatwhichJavaclassesactuallystartrunning.

Sooneofthethingsyoushouldthinknow,youneverwroteamethodcalledmain.Ineversawamethodcalledmain,andyou'

retellingmethat'

swhereJavaprogramsactuallystartrunning.Yeah,infactitis.It'

sbecauseprogramsprovidedthismainmethodforyou.Whatthismainmethoddidintheprogramwasessentiallygettherestofyouprogramrunningbygettingafewthingssetupandthenkickingoffyourrunmethod.Soyoudidn'

tactuallyneedtoworryaboutthis.

Butnowyou'

resortofoldenoughtoactuallyseewhatthatmainmethodisallabout.Soifwethinkaboutwhatthismainmethoddoes,theheaderforthemainmethodisalsokindofweird.Thisispartofthereasonwhywenevershowedyouthemainmethodbefore.Theheaderforthemainmethodisactuallypublicstaticvoidmain,butwe'

renotdoneyet.Mainactuallyhassomearguments.Ithasanarrayofstringscalledargsandarguments,andthensomethinginherehappensinsideofme.

Ifweshowedthistoyouonthefirstday,wewould'

vehadtogothroughandexplainwhatallthesewordsmeantbeforeweexplainedwhatmainevenwas,beforeweexplainedhowyouwriteyourfirstprogram.Thatwould'

vebeenapain.Nowwecanjusttellyou.Publicmainsisapublicmethod.Youknowthat.Youprobablyrecalltheotherpublicmethodsyou'

vewritten.Staticmeansthatthisisactuallyamethodthatbelongstotheclass?

it'

snotsomethingthatyouwouldactuallycallonaparticularobject.

Soyouneverhavesomeobject?

like,here'

smyobjectX,andIcallX.main.Mainisjustsomethingthatgetscalled.It'

saclassmethodasopposedtobeingamethodthatgetscalledonaninstance.Voidmeansitjustreturnsnothing.

Whatisgettingpassedinhereisanarrayofstrings.Whereisthatarrayofstringscomingfrom?

Thisactuallyharksbacktowhencomputersweren'

tallniceandgraphicalandeverything.Whenpeoplewroteprograms,thewroteprogramandweretypingonwhat'

scalledacommandline.Theywrongthenameoftheprogramout.Theyactuallytypedit,andthentheytypedabunchofthingsthattheywantedtobepassedintotheprogramsuchasinitialinformationtostartthatprogram.Thatwastheinitialthing,soifyouhadsomeprogramlikenamesurfer,youmightactuallystartoffbygivingthenameoftheprogram.

Thenafternamesurfer,youmightgiveitthenameofthedatafile,likedatadottext.Youmight'

vegivenitsomeotherthingsaswellthatwereseparatedbyspaces.Thislistofstuffisessentiallywhatgetspassedinhereasarguments.They'

restrings,andthisishowtheprogramwouldactuallyknowwhatcameinonthecommandlinewhentheprogramwaskickedoff.Java'

snotthatoldofalanguage.Itsortofcamearoundandgainingpopularityin1995.Peopleweren'

tdoingalotofthisin1995.Ialreadyhadmymouseandmyfoldersandallthisotherstuff,evenifyouweresixyearsold.Youprobablydid.

You'

relike,Inevertypedthisstuff,sowhydoIcareaboutit?

ThereasonwhyJava'

sderivedfromanotherlanguagecalledC,andthere'

savariationcalledC++thatwascreatedwhenpeoplewerewritingprogramsinthedaysofyore.Thewholenotionofmainandhavingsomeargumentstogetpassedtomainkindofcamealongwiththebaggageofactuallyhavingaprogramlanguagethatmatchesthesamestyleprogramminglanguageswhentheydiddothis.

SoalotofthetimesinrealJavaprogramsthesedays,therearen'

treallyanyarguments.Iftherearearguments,there'

ssomesystemparametersorsomethinglikethat.Wedon'

tusuallyworryaboutthem.SowhenyougoandlookatsomeotherJavaprogramthatisn'

tusingtheACMlibrariesandyouseethismainthing,andyou'

rewonderingwhatit'

sallabout,youcanthinkofmainanalogouslytorun.It'

sjustwherethewholetimeyou'

vebeenthinkingofrunaswhereyou'

reexecutionstarts,mainisreallywhereexecutionstarted.

Ifyouthinkaboutexecutionactuallystartedinmain,sohowdidthisthingactuallykickoffmyrunmethod?

Nowyou'

resortofoldenoughtoseethat,too.Sowhatitactuallydid?

let'

ssaythiswasthemainmethodissomethinglikenamesurfer.Sosomewhereinsideofaprogram,insideoftheACMlibrariesforprogram,wehadthismainmethodthatfiguredoutwhatthenameofyourclasswas.Essentially,ithadaone-linerinitthatwould'

vebeenequivalenttothis.

Newnamesurferdotstartcards.Soit'

saoneliner.Nowyouknowwhatthismeans.Whatwasitactuallydoing?

Whenmainst