java语言程序设计基础篇第八版英文课件(第12章)

Chapter12GUIBasics1MotivationsThedesignoftheAPIforJavaGUIprogrammingisanexcellentexampleofhowtheobject-orientedprincipleisapplied.Inthechaptersthatfollow,youwilllearntheframeworkofJavaGUIAPIandusetheGUIcomponentstodevelopuser-friendlyinterfacesforapplicationsandapplets.2ObjectivesTodistinguishbetweenSwingandAWT(§12.2).TodescribetheJavaGUIAPIhierarchy(§12.3).Tocreateuserinterfacesusingframes,panels,andsimpleGUIcomponents(§12.4).Tounderstandtheroleoflayoutmanagers(§12.5).TousetheFlowLayout,GridLayout,andBorderLayoutmanagerstolayoutcomponentsinacontainer(§12.5).TouseJPanelassubcontainers(§12.7).TospecifycolorsandfontsusingtheColorandFontclasses(§§12.7-12.8).Toapplycommonfeaturessuchasborders,tooltips,fonts,andcolorsonSwingcomponents(§12.9).Touseborderstovisuallygroupuser-interfacecomponents(§12.9).TocreateimageiconsusingtheImageIconclass(§12.10).3CreatingGUIObjects//CreateabuttonwithtextOKJButtonjbtOK=newJButton("OK");

//Createalabelwithtext"Enteryourname:"JLabeljlblName=newJLabel("Enteryourname:");

//Createatextfieldwithtext"TypeNameHere"JTextFieldjtfName=newJTextField("TypeNameHere");

//CreateacheckboxwithtextboldJCheckBoxjchkBold=newJCheckBox("Bold");

//CreatearadiobuttonwithtextredJRadioButtonjrbRed=newJRadioButton("Red");

//Createacomboboxwithchoicesred,green,andblueJComboBoxjcboColor=newJComboBox(newString[]{"Red","Green","Blue"});4ButtonLabelTextfieldCheckBoxRadioButtonComboBoxSwingvs.AWTSowhydotheGUIcomponentclasseshaveaprefixJ?InsteadofJButton,whynotnameitsimplyButton?Infact,thereisaclassalreadynamedButtoninthejava.awtpackage.WhenJavawasintroduced,theGUIclasseswerebundledinalibraryknownastheAbstractWindowsToolkit(AWT).ForeveryplatformonwhichJavaruns,theAWTcomponentsareautomaticallymappedtotheplatform-specificcomponentsthroughtheirrespectiveagents,knownaspeers.AWTisfinefordevelopingsimplegraphicaluserinterfaces,butnotfordevelopingcomprehensiveGUIprojects.Besides,AWTispronetoplatform-specificbugsbecauseitspeer-basedapproachreliesheavilyontheunderlyingplatform.WiththereleaseofJava2,theAWTuser-interfacecomponentswerereplacedbyamorerobust,versatile,andflexiblelibraryknownasSwingcomponents.SwingcomponentsarepainteddirectlyoncanvasesusingJavacode,exceptforcomponentsthataresubclassesofjava.awt.Windoworjava.awt.Panel,whichmustbedrawnusingnativeGUIonaspecificplatform.SwingcomponentsarelessdependentonthetargetplatformanduselessofthenativeGUIresource.Forthisreason,Swingcomponentsthatdon’trelyonnativeGUIarereferredtoaslightweightcomponents,andAWTcomponentsarereferredtoasheavyweightcomponents.5GUIClassHierarchy(Swing)6ContainerClasses7ContainerclassescancontainotherGUIcomponents.GUIHelperClasses8ThehelperclassesarenotsubclassesofComponent.TheyareusedtodescribethepropertiesofGUIcomponentssuchasgraphicscontext,colors,fonts,anddimension.SwingGUIComponents9ComponentsCoveredintheBriefVersion10ComponentsCoveredintheComprehensiveVersion11AWT(Optional)12FramesFrameisawindowthatisnotcontainedinsideanotherwindow.FrameisthebasistocontainotheruserinterfacecomponentsinJavaGUIapplications.TheJFrameclasscanbeusedtocreatewindows.ForSwingGUIprograms,useJFrameclasstocreatewidows.13CreatingFrames14Runimportjavax.swing.*;publicclassMyFrame{publicstaticvoidmain(String[]args){JFrameframe=newJFrame("TestFrame");frame.setSize(400,300);frame.setVisible(true);frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);}}MyFrameAddingComponentsintoaFrame15//Addabuttonintotheframeframe.getContentPane().add(newJButton("OK"));RunMyFrameWithComponentsTitlebarContentpaneContentPaneDelegationinJDK1.516//Addabuttonintotheframeframe.getContentPane().add(newJButton("OK"));TitlebarContentpane//Addabuttonintotheframeframe.add(newJButton("OK"));JFrameClass17LayoutManagersJava’slayoutmanagersprovidealevelofabstractiontoautomaticallymapyouruserinterfaceonallwindowsystems.TheUIcomponentsareplacedincontainers.EachcontainerhasalayoutmanagertoarrangetheUIcomponentswithinthecontainer.LayoutmanagersaresetincontainersusingthesetLayout(LayoutManager)methodinacontainer.18KindsofLayoutManagersFlowLayout(Chapter13)GridLayout(Chapter13)BorderLayout(Chapter13)SeveralotherlayoutmanagerswillbeintroducedinChapter33,“Containers,LayoutManagers,andBorders”19FlowLayoutExampleWriteaprogramthataddsthreelabelsandtextfieldsintothecontentpaneofaframewithaFlowLayoutmanager.20ShowFlowLayoutRunTheFlowLayoutClass21GridLayoutExampleRewritetheprogramintheprecedingexampleusingaGridLayoutmanagerinsteadofaFlowLayoutmanagertodisplaythelabelsandtextfields.22ShowGridLayoutRunTheGridLayoutClass23TheBorderLayoutManagerTheBorderLayoutmanagerdividesthecontainerintofiveareas:East,South,West,North,andCenter.ComponentsareaddedtoaBorderLayoutbyusingtheaddmethod.24add(Component,constraint),whereconstraintisBorderLayout.EAST,BorderLayout.SOUTH,BorderLayout.WEST,BorderLayout.NORTH,orBorderLayout.CENTER.

BorderLayoutExample25ShowBorderLayoutRunTheBorderLayoutClass26TheColorClassYoucansetcolorsforGUIcomponentsbyusingthejava.awt.Colorclass.Colorsaremadeofred,green,andbluecomponents,eachofwhichisrepresentedbyabytevaluethatdescribesitsintensity,rangingfrom0(darkestshade)to255(lightestshade).ThisisknownastheRGBmodel.Colorc=newColor(r,g,b);r,g,andbspecifyacolorbyitsred,green,andbluecomponents.Example:Colorc=newColor(228,100,255);27StandardColorsThirteenstandardcolors(black,blue,cyan,darkGray,gray,green,lightGray,magenta,orange,pink,red,white,yellow)aredefinedasconstantsinjava.awt.Color.Thestandardcolornamesareconstants,buttheyarenamedasvariableswithlowercaseforthefirstwordanduppercaseforthefirstlettersofsubsequentwords.ThusthecolornamesviolatetheJavanamingconvention.SinceJDK1.4,youcanalsousethenewconstants:BLACK,BLUE,CYAN,DARK_GRAY,GRAY,GREEN,LIGHT_GRAY,MAGENTA,ORANGE,PINK,RED,WHITE,andYELLOW.28SettingColorsYoucanusethefollowingmethodstosetthecomponent’sbackgroundandforegroundcolors:setBackground(Colorc)setForeground(Colorc)Example:jbt.setBackground(Color.yellow);jbt.setForeground(Color.red);29TheFontClassFontmyFont=newFont(name,style,size);Example:FontmyFont=newFont("SansSerif",Font.BOLD,16);FontmyFont=newFont("Serif",Font.BOLD+Font.ITALIC,12);JButtonjbtOK=newJButton("OK“);jbtOK.setFont(myFont);30FontNamesStandardfontnamesthataresupportedinallplatformsare:SansSerif,Serif,Monospaced,Dialog,orDialogInput.FontStyleFont.PLAIN(0),Font.BOLD(1),Font.ITALIC(2),andFont.BOLD+Font.ITALIC(3)FindingAllAvailableFontNamesGraphicsEnvironmente=GraphicsEnvironment.getLocalGraphicsEnvironment();String[]fontnames=e.getAvailableFontFamilyNames();for(inti=0;i<fontnames.length;i++)System.out.println(fontnames[i]);31UsingPanelsasSub-ContainersPanelsactassub-containersforgroupinguserinterfacecomponents.Itisrecommendedthatyouplacetheuserinterfacecomponentsinpanelsandplacethepanelsinaframe.Youcanalsoplacepanelsinapanel.ToaddacomponenttoJFrame,youactuallyaddittothecontentpaneofJFrame.Toaddacomponenttoapanel,youadditdirectlytothepanelusingtheaddmethod.32CreatingaJPanelYoucanusenewJPanel()tocreateapanelwithadefaultFlowLayoutmanagerornewJPanel(LayoutManager)tocreateapanelwiththespecifiedlayoutmanager.Usetheadd(Component)methodtoaddacomponenttothepanel.Forexample,JPanelp=newJPanel();p.add(newJButton("OK"));33TestingPanelsExampleThisexampleusespanelstoorganizecomponents.TheprogramcreatesauserinterfaceforaMicrowaveoven.

34TestPanelsRunCommonFeaturesofSwingComponents35BordersYoucansetaborderonanyobjectoftheJComponentclass.Swinghasseveraltypesofborders.Tocreateatitledborder,usenewTitledBorder(Stringtitle).Tocreatealineborder,usenewLineBorder(Colorcolor,intwidth),wherewidthspecifiesthethicknessoftheline.Forexample,thefollowingcodedisplaysatitledborderonapanel:JPanelpanel=newJPanel();panel.setBorder(newTitleBorder(“My