Applets

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Applets
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Applets

• Design of Applets

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Design of Applets

• Sun wrote Java to be executable within a hosting
  application
• browser
• The applications are applets.
• An applet is downloaded to the local client
  application and run on the local java-enabled
  machine
• All ordinary capability except file output and
  database input or output is easily available

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Design of Applets

• An Applet is run inside of another application
• Browser
• AppletViewer
• The programmer adds panels with their controls to
  browsers content panel (the web page)

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Design of Applets

• There are five major methods in an Applet
• init () called when Applet starts
• start () called when page is displayed
• stop () called when user exits
• destroy () called when resources are lost
• paint () called when Applet is refreshed

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Design of Applets

• Sample codepublic class Program4 extends
  JApplet
• public void init ()
• getContentPane ( ).add(myPanel)
• Where myPanel is the one of the panels containing
  controls

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Design of Applets

• Design of Hosting Web Page (use of Applet tag)
• ltbodygt
• ltapplet codemyservlets.AdderApplet.class
• width550 height400gt
• ltparam namehost value
• "http//localhost8080/user002/servlet/myservlet
  s.AdderServlet"gt
• lt/appletgt
• lt/bodygt
• Where host is an argument sent to the Applet from
  the web page

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GUI Applications

• Using a frame
• public class Example extends JFrame
• public Example ( )
• getContentPane( ).add(myPanel)
• public static void main (String args )
• Example example new Example (Example)
• example.setTitle (aTitle)
• example.setSize (300, 250)
• example.setDefaultCloseOperation (3)
• example.setVisible(true)

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GUI Application as Applet

• Init and handle events
• public class Example extends JApplet
• public void init ( )
• getContentPane( ).add(myPanel)
• setTitle (aTitle)
• setSize (300, 250)
• setDefaultCloseOperation (3)
• setVisible(true)
• See ConvertTemperatures applet, and note change
  from application

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Summary

• Applets are a window system
• One can also place windows in a frame and use
  them in an application
• Applets significantly bring web-based
  applications to life by moving the work to the
  client machine
• Error checking can be decentralized from the
  server to the clients