java语言程序设计 基础篇原书第八版课件 PPT(第十五章).ppt

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1、Chapter15Graphics1MotivationsIfyouwanttodrawshapessuchasabarchart,aclock,orastopsign,howdoyoudoit?2ObjectivesFTodescribeJavacoordinatesystemsinaGUIcomponent(15.2).FTodrawthingsusingthemethodsintheGraphicsclass(15.3).FTooverridethepaintComponentmethodtodrawthingsonaGUIcomponent(15.3).FTouseapanelasac

2、anvastodrawthings(15.3).FTodrawstrings,lines,rectangles,ovals,arcs,andpolygons(15.4,15.6-15.7).FToobtainfontpropertiesusingFontMetricsandknowhowtocenteramessage(15.8).FTodisplayanimageinaGUIcomponent(15.11).FTodevelopreusableGUIcomponentsFigurePanel,MessagePanel,StillClock,andImageViewer(15.5,15.9,1

3、5.10,15.12).3JavaCoordinateSystem4EachGUIComponentHasitsOwnCoordinateSystem5TheGraphicsClassYoucandrawstrings,lines,rectangles,ovals,arcs,polygons,andpolylines,usingthemethodsintheGraphicsclass.6paintComponentExampleInordertodrawthingsonacomponent,youneedtodefineaclassthatextendsJPanelandoverridesit

4、spaintComponentmethodtospecifywhattodraw.ThefirstprograminthischaptercanberewrittenusingpaintComponent.TestPaintComponentRun7DrawingGeometricFiguresFDrawingStringsFDrawingLinesFDrawingRectanglesFDrawingOvalsFDrawingArcsFDrawingPolygons8DrawingStringsdrawLine(intx1,inty1,intx2,inty2);drawString(Strin

5、gs,intx,inty);9DrawingRectanglesdrawRect(intx,inty,intw,inth);fillRect(intx,inty,intw,inth);10DrawingRoundedRectanglesdrawRoundRect(intx,inty,intw,inth,intaw,intah);fillRoundRect(intx,inty,intw,inth,intaw,intah);11DrawingOvalsdrawOval(intx,inty,intw,inth);fillOval(intx,inty,intw,inth);12CaseStudy:Th

6、eFigurePanelClassThisexampledevelopsausefulclassfordisplayingvariousfigures.Theclassenablestheusertosetthefiguretypeandspecifywhetherthefigureisfilled,anddisplaysthefigureonapanel.FigurePanel13TestFigurePanelThisexampledevelopsausefulclassfordisplayingvariousfigures.Theclassenablestheusertosetthefig

7、uretypeandspecifywhetherthefigureisfilled,anddisplaysthefigureonapanel.TestFigurePanelRun14DrawingArcsdrawArc(intx,inty,intw,inth,intangle1,intangle2);fillArc(intx,inty,intw,inth,intangle1,intangle2);Anglesareindegree15DrawingArcsExampleDrawArcsRun16DrawingPolygonsandPolylinesintx=40,70,60,45,20;int

8、y=20,40,80,45,60;g.drawPolygon(x,y,x.length);g.drawPolyline(x,y,x.length);17DrawingPolygonsUsingthePolygonClassPolygonpolygon=newPolygon();polygon.addPoint(40,59);polygon.addPoint(40,100);polygon.addPoint(10,100);g.drawPolygon(polygon);18DrawingPolygonsExampleDrawPolygonRun19CenteringDisplayUsingthe

9、FontMetricsClassYoucandisplayastringatanylocationinapanel.Canyoudisplayitcentered?Todoso,youneedtousetheFontMetricsclasstomeasuretheexactwidthandheightofthestringforaparticularfont.AFontMetricscanmeasurethefollowingattributes:FpublicintgetAscent()FpublicintgetDescent()FpublicintgetLeading()getAscent

10、()getLeading()getDescent()getHeight()FpublicintgetHeight()FpublicintstringWidth(Stringstr)20TheFontMetricsClassFontMetricsisanabstractclass.TogetaFontMetricsobjectforaspecificfont,usethefollowinggetFontMetricsmethodsdefinedintheGraphicsclass:publicFontMetricsgetFontMetrics(Fontf)Returnsthefontmetric

11、softhespecifiedfont.publicFontMetricsgetFontMetrics()Returnsthefontmetricsofthecurrentfont.21TestCenterMessageRun22CaseStudy:MessagePanelMessagePanelRunThiscasestudydevelopsausefulclassthatdisplaysamessageinapanel.Theclassenablestheusertosetthelocationofthemessage,centerthemessage,andmovethemessagew

12、iththespecifiedinterval.TestMessagePanel23CaseStudy:StillClockDisplayClockRunStillClock24DrawingClockxEnd=xCenter+handLengthsin()yEnd=yCenter-handLengthcos()Sincetherearesixtysecondsinoneminute,theangleforthesecondhandissecond(2/60)25DrawingClock,cont.xEnd=xCenter+handLengthsin()yEnd=yCenter-handLen

13、gthcos()Thepositionoftheminutehandisdeterminedbytheminuteandsecond.Theexactminutevaluecombinedwithsecondsisminute+second/60.Forexample,ifthetimeis3minutesand30seconds.Thetotalminutesare3.5.Sincetherearesixtyminutesinonehour,theanglefortheminutehandis(minute+second/60)(2/60)26DrawingClock,cont.xEnd=x

14、Center+handLengthsin()yEnd=yCenter-handLengthcos()Sinceonecircleisdividedintotwelvehours,theangleforthehourhandis(hour+minute/60+second/(6060)(2/12)27DisplayingImageIconsYoulearnedhowtocreateimageiconsanddisplayimageiconsinlabelsandbuttons.Forexample,thefollowingstatementscreateanimageiconanddisplay

15、itinalabel:ImageIconicon=newImageIcon(image/us.gif);JLabeljlblImage=newJLabel(imageIcon);Animageicondisplaysafixed-sizeimage.Todisplayanimageinaflexiblesize,youneedtousethejava.awt.Imageclass.AnimagecanbecreatedfromanimageiconusingthegetImage()methodasfollows:Imageimage=imageIcon.getImage();28Displa

16、yingImagesUsingalabelasanareafordisplayingimagesissimpleandconvenient,butyoudonthavemuchcontroloverhowtheimageisdisplayed.AmoreflexiblewaytodisplayimagesistousethedrawImagemethodoftheGraphicsclassonapanel.FourversionsofthedrawImagemethodareshownhere.29DisplayingImagesExampleThisexamplegivesthecodeth

17、atdisplaysanimagefromimage/us.gif.Thefileimage/us.gifisundertheclassdirectory.TheImagefromthefileiscreatedintheprogram.ThedrawImagemethoddisplaystheimagetofillinthewholepanel,asshowninthefigure.RunDisplayImage30CaseStudy:ImageViewerClassDisplayinganimageisacommontaskinJavaprogramming.ThiscasestudydevelopsareusablecomponentnamedImageViewerthatdisplaysanimageinapanel.TheImageViewerclasscontainsthepropertiesimage,imageFilename,stretched,xCoordinate,andyCoordinate.31ImageViewExampleThisexamplegivesanexamplethatcreatessiximagesusingtheImageViewerclass.RunSixFlags32