Applet

General info

• An applet is a Java class and a small program.
• An applet can not be run in a stand-alone mode. It must be run in a Web browser.
• An applet is graphical in nature.
• Use HTML tag to configure and call applet.
• Use Appletviewer to look at applet without web browser.
• Use an applet
• Applet class structure
• Key methods.
• Life cycle.
• Use tag to configure and call applet
• Security.
• JApplet

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Use an applet

• Load URL
• Load the HTML document
• Load applet classes
• Run the applet

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Applet class structure

java.lang.Object
	java.awt.Component
		java.awt.Container
			java.awt.Window 
				java.awt.Frame
			java.awt.Panel
				java.applet.Applet

• Applet is a subclass of Panel.
• Applet class must be the superclass of any applet.
• Applet's layout manager is FlowLayout.

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Key Methods

• init()
• start()
• stop()
• destroy()
• paint(), repaint(), update()

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Life cycle

• init(): Called when the applet is created, used to initialize data values
• start(): Called when the applet becomes visible
• stop(): Called when the applet becomes invisible

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Use tag to configure and call applet

<applet
[archive=archiveList]
code=appletFile.class
width=pixels height=pixels
[codebase=codebaseURL]
[alt=alternateText]
[name=appletInstanceName]
[align=alignment]
[vspace=pixels] [hspace=pixels]
>
[<param name=appletAttribute1 value=value>]
[<param name=appletAttribute2 value=value>]
. . .
[alternateHTML]
</applet>

• getDocumentBase() – Returns a URL object that describes the directory of the current browser page
• getCodeBase() – Returns a URL object that describes the source directory of the applet class
• getImage(URL base, String target) and
• getAudioClip(URL base, String target) – Use theURL object as a starting point
  --play(URL soundDirectory, String soundFile);
  --play(URL soundURL);
  

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Security

• Runtime execution of another program.
• File I/O (input/output).
• Calls to any native methods.
• Attempts to open a socket to any system except the host that provided the applet.

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JApplet

• A Swing package component.
• class structure:

  java.lang.Object
  	java.awt.Component
  		java.awt.Container
  			java.awt.Window 
  				java.awt.Frame
  			java.awt.Panel
  				java.applet.Applet
                                        javax.swing.JApplet
  

• JApplet is a subclass of Applet.
• A slightly incompatible with Applet.
• BorderLayout manager.

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