Java: Applets and AWT

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Java Applets and AWT
Peter T. Breuer Universidad Carlos III de
Madrid ltptb_at_it.uc3m.esgt
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Hierarchy

• Object
• Component
• Container
• Panel
• Applet

java.lang
java.awt
java.applet
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java.applet

• public class Applet extends Panel
• public abstract interface AppletContext
• allows the applet to interact with the browser or
  viewer
• public abstract interface AppletStub
• internal interface
• public abstract interface AudioClip
• describes the methods and audio clip must have

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Some applet methods

• void init() called when applet is first loaded
• void start() called when the applet becomes
  visible
• void stop() called when applet becomes
  temporarily invisible
• void destroy() called when applet is about to
  the unloaded

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Some more applet methods

• String getParameter(String name) gets a
  parameter from the html page
• void showStatus(String msg) displays text in the
  status line
• Image getImage(URL url) reads an image from the
  net
• URL getCodeBase() returns the base URL from
  which the applet was called
• any many others...

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Some inherited methods

• paint() called when the applet has to be drawn
  on the screen

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Parameter passing

• ltapplet code"x.class" width"10"
  height"10"gtltparam name"number"
  value"123"gtltparam name"image"
  value"img.gif"gtltparam name"sound"
  value"snd.au"gt lt/appletgt
• String xgetParameter("number")

.html
.java
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jar files

• Command that allows to compress a numbers of
  files (like tar)
• ltapplet archive"x.jar" code"x.class" width"10"
  height"10"gt ... lt/appletgt
• The browser first searches for the needed file in
  the jar file, and if not found, tries to load the
  file as usual

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Abstract Windowing Toolkit

• It contains classes for
• Graphics (colors, fonts, images, ...)
• Components (buttons, menus, lists, ...)
• Layout Managers (for the control of objects
  within container objects)

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Graphics classes in AWT

• Color
• Cursor
• Dimension
• Font
• FontMetrics
• Graphics
• Image
• Insets

• MediaTracker
• Point
• Polygon
• PrintJob
• Rectangle
• Toolkit

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Component classes in AWT

• Component
• Checkbox
• Choice
• List
• Button
• Canvas
• Container
• Label
• ScrollBar
• TextComponent

• CheckboxGroup
• MenuComponent
• MenuShortcut

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Layout classes in AWT

• FlowLayout
• GridLayout
• GridBagConstraints
• BorderLayout
• CardLayout
• GridBagLayout