外文原文JAVAEVENTSAREPARTOFTHEJAVAAWTABSTRACTWINDOWINGTOOLKITPACKAGEANEVENTISTHEWAYTHATTHEAWTCOMMUNICATESTOYOU,ASTHEPROGRAMMER,ANDTOOTHERJAVAAWTCOMPONENTSTHATSOMETHINGHASHAPPENEDTHATSOMETHINGCANBEINPUTFROMTHEUSERMOUSEMOVEMENTSORCLICKS,KEYPRESSES,CHANGESINTHESYSTEMENVIRONMENTAWINDOWOPENINGORCLOSING,THEWINDOWBEINGSCROLLEDUPORDOWN,ORAHOSTOFOTHERTHINGSTHATMIGHT,INSOMEWAY,BEINTERESTINGTOTHEOPERATIONOFTHEPROGRAMNOTEJAVASABSTRACTWINDOWINGTOOLKITISAPACKAGEOFCLASSESTHATIMPLEMENTSMOSTCOMMONUICOMPONENTS,SUCHASWINDOWS,BUTTONS,MENUS,ANDSOONITISALSOSPECIFICALLYTHEAWT,ANDNOTJAVA,THATGENERATESANDMANAGESEVENTSINOTHERWORDS,WHENEVERJUSTABOUTANYTHINGHAPPENSTOAJAVAAWTCOMPONENT,INCLUDINGANAPPLET,ANEVENTISGENERATEDSOMEEVENTSAREHANDLEDBYTHEAWTORBYTHEBROWSERWITHOUTYOURNEEDINGTODOANYTHINGPAINTMETHODS,FOREXAMPLE,AREGENERATEDANDHANDLEDBYTHEBROWSERALLYOUHAVETODOISTELLTHEAWTWHATYOUWANTPAINTEDWHENITGETSTOYOURPARTOFTHEWINDOWSOMEEVENTS,HOWEVERFOREXAMPLE,AMOUSECLICKINSIDETHEBOUNDARIESOFYOURAPPLETYOUMAYNEEDTOKNOWABOUTWRITINGYOURJAVAPROGRAMSTOHANDLETHESEKINDSOFEVENTSENABLESYOUTOGETINPUTFROMTHEUSERANDHAVEYOURAPPLETCHANGEITSBEHAVIORBASEDONTHATINPUTTODAY,YOULLLEARNABOUTMANAGINGSIMPLEEVENTS,INCLUDINGTHEFOLLOWINGBASICSNNMOUSECLICKSNNMOUSEMOVEMENTS,INCLUDINGMOUSEDRAGGINGNNKEYBOARDACTIONSYOULLALSOLEARNABOUTTHEHANDLEEVENTMETHOD,WHICHISTHEBASISFORCOLLECTING,HANDLING,ANDPASSINGONEVENTSOFALLKINDSFROMYOURAPPLETTOOTHERUICOMPONENTSINTHEWINDOWORINYOURAPPLETITSELFTOMORROW,YOULLLEARNHOWTOCOMBINEEVENTSWITHTHEAWTTOCREATEACOMPLETEINTERFACEFORYOURAPPLETMOUSECLICKSLETSSTARTWITHTHEMOSTCOMMONEVENTYOUMIGHTBEINTERESTEDINMOUSECLICKSMOUSECLICKEVENTSOCCURWHENYOURUSERCLICKSTHEMOUSESOMEWHEREINTHEBODYOFYOURAPPLETYOUCANINTERCEPTMOUSECLICKSTODOVERYSIMPLETHINGSFOREXAMPLE,TOTOGGLETHESOUNDONANDOFFINYOURAPPLET,TOMOVETOTHENEXTSLIDEINAPRESENTATION,ORTOCLEARTHESCREENANDSTARTOVERORYOUCANUSEMOUSECLICKSINCONJUNCTIONWITHMOUSEMOVEMENTSTOPERFORMMORECOMPLEXMOTIONSINSIDEYOURAPPLETMOUSEDOWNANDMOUSEUPWHENYOUCLICKTHEMOUSEONCE,THEAWTGENERATESTWOEVENTSAMOUSEDOWNEVENTWHENTHEMOUSEBUTTONISPRESSED,ANDAMOUSEUPEVENTWHENTHEBUTTONISRELEASEDWHYTWOINDIVIDUALEVENTSFORASINGLEMOUSEACTIONBECAUSEYOUMAYWANTTODODIFFERENTTHINGSFORTHE“DOWN”ANDTHE“UP”FOREXAMPLE,LOOKATAPULLDOWNMENUTHEMOUSEDOWNEXTENDSTHEMENU,ANDTHEMOUSEUPSELECTSANITEMWITHMOUSEDRAGSBETWEENBUTYOULLLEARNABOUTTHATONELATERIFYOUHAVEONLYONEEVENTFORBOTHACTIONSMOUSEUPANDMOUSEDOWN,YOUCANNOTIMPLEMENTTHATSORTOFUSERINTERACTIONHANDLINGMOUSEEVENTSINYOURAPPLETISEASYALLYOUHAVETODOISOVERRIDETHERIGHTMETHODDEFINITIONINYOURAPPLETTHATMETHODWILLBECALLEDWHENTHATPARTICULAREVENTOCCURSHERESANEXAMPLEOFTHEMETHODSIGNATUREFORAMOUSEDOWNEVENTPUBLICBOOLEANMOUSEDOWNEVENTEVT,INTX,INTYTHEMOUSEDOWNMETHODANDTHEMOUSEUPMETHODASWELLTAKESTHREEPARAMETERSTHEEVENTITSELFANDTHEXANDYCOORDINATESWHERETHEMOUSEDOWNORMOUSEUPEVENTOCCURREDTHEEVENTARGUMENTISANINSTANCEOFTHECLASSEVENTALLSYSTEMEVENTSGENERATEANINSTANCEOFTHEEVENTCLASS,WHICHCONTAINSINFORMATIONABOUTWHEREANDWHENTHEEVENTTOOKPLACE,THEKINDOFEVENTITIS,ANDOTHERINFORMATIONTHATYOUMIGHTWANTTOKNOWABOUTTHISEVENTSOMETIMESHAVINGAHANDLETOTHATEVENTOBJECTISUSEFUL,ASYOULLDISCOVERLATERONINTHISSECTIONTHEXANDTHEYCOORDINATESOFTHEEVENT,ASPASSEDINTHROUGHTHEXANDYARGUMENTS,AREPARTICULARLYNICETOKNOWBECAUSEYOUCANUSETHEMTODETERMINEPRECISELYWHERETHEMOUSECLICKTOOKPLACEFOREXAMPLE,HERESASIMPLEMETHODTHATPRINTSOUTINFORMATIONABOUTAMOUSEDOWNWHENITOCCURSPUBLICBOOLEANMOUSEDOWNEVENTEVT,INTX,INTYSYSTEMOUTPRINTLN“MOUSEDOWNAT“X“,”YRETURNTRUEBYINCLUDINGTHISMETHODINYOURAPPLET,EVERYTIMEYOURUSERCLICKSTHEMOUSEINSIDEYOURAPPLET,THISMESSAGEWILLGETPRINTEDNOTETHATTHISMETHOD,UNLIKETHEOTHERSYSTEMMETHODSYOUVESTUDIEDTHISFAR,RETURNSABOOLEANVALUEINSTEADOFNOTRETURNINGANYTHINGVOIDTHISWILLBECOMEIMPORTANTTOMORROWWHENYOUCREATEUSERINTERFACESANDTHENMANAGEINPUTTOTHESEINTERFACESHAVINGANEVENTHANDLERRETURNTRUEORFALSEDETERMINESWHETHERAGIVENUICOMPONENTCANINTERCEPTANEVENTORWHETHERITNEEDSTOPASSITONTOTHEENCLOSINGCOMPONENTTHEGENERALRULEISTHATIFYOURMETHODDEALSWITHTHEEVENT,ITSHOULDRETURNTRUE,WHICHFORTHEFOCUSOFTODAYSLESSONISALMOSTALWAYSTHECASETHESECONDHALFOFTHEMOUSECLICKISTHEMOUSEUPMETHOD,WHICHISCALLEDWHENTHEMOUSEBUTTONISRELEASEDTOHANDLEAMOUSEUPEVENT,ADDTHEMOUSEUPMETHODTOYOURAPPLETMOUSEUPLOOKSJUSTLIKEMOUSEDOWNPUBLICBOOLEANMOUSEUPEVENTEVT,INTX,INTYANEXAMPLESPOTSINTHISSECTION,YOULLCREATEANEXAMPLEOFANAPPLETTHATUSESMOUSEEVENTSMOUSEDOWNEVENTSINPARTICULARTHESPOTSAPPLETSTARTSWITHABLANKSCREENANDTHENSITSANDWAITSWHENYOUCLICKTHEMOUSEONTHATSCREEN,ABLUEDOTISDRAWNYOUCANPLACEUPTOTENDOTSONTHESCREENFIGURE121SHOWSTHESPOTSAPPLETLETSSTARTFROMTHEBEGINNINGANDBUILDTHISAPPLET,STARTINGFROMTHEINITIALCLASSDEFINITIONIMPORTJAVAAWTGRAPHICSIMPORTJAVAAWTCOLORIMPORTJAVAAWTEVENTPUBLICCLASSSPOTSEXTENDSJAVAAPPLETAPPLETFINALINTMAXSPOTS10INTXSPOTSNEWINTMAXSPOTSINTYSPOTSNEWINTMAXSPOTSINTCURRSPOTS0THISCLASSUSESTHREEOTHERAWTCLASSESGRAPHICS,COLOR,ANDEVENTTHATLASTCLASS,EVENT,NEEDSTOBEIMPORTEDINANYAPPLETSTHATUSEEVENTSTHECLASSHASFOURINSTANCEVARIABLESACONSTANTTODETERMINETHEMAXIMUMNUMBEROFSPOTSTHATCANBEDRAWN,TWOARRAYSTOSTORETHEXANDYCOORDINATESOFTHESPOTSTHATHAVEALREADYBEEND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