Appletcations

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"Appletcations"
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Applets and applications

• You create an applet by extending Applet
• You may, but are not required to, override
  methods of Applet init, start, paint, stop,
  destroy
• An application requires a public static void
  main(String args) method
• You can create an "appletcation" by simply doing
  all of the above

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Hello1.java
import java.awt. import java.applet.Applet pub
lic class Hello1 extends Applet public void
paint(Graphics g) g.drawString("Hello
World!", 30, 30)
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Hello1.html
ltapplet code"Hello1.class"
width"250" height"100"gt lt/appletgt

• I won't bother showing the HTML after this

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Hello2.java
public static void main(String args)
Frame myFrame new Frame("Hello2") Applet
myApplet new Hello2( ) myFrame.add(myApplet
, BorderLayout.CENTER)
myFrame.setSize(250, 100) myApplet.init(
) myApplet.start( ) myFrame.setVisible(t
rue)
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Closing

• Hello2.java works fine, but...
• ...You can't close the window by clicking the x
  in the upper-right corner you have to use Ctrl-C
• You can fix this by adding implementing
  WindowListener or better yet, by extending
  WindowAdapter

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Hello3.java
import java.awt.event.
Add to main myFrame.addWindowListener(new
myCloser())
New classclass myCloser extends WindowAdapter
public void windowClosing(WindowEvent event)
System.exit(0)
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Adding stop( ) and destroy( )

• Applets sometimes (but rarely) use stop( ) and
  destroy( )
• These should be called in windowClosing( )
• To do this, windowClosing( ) must have access to
  the Applet's methods, hence to the Applet itself
• The Applet can be made a static member of its own
  class

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Hello4.java
public class Hello4 extends Applet //
myApplet has been moved and made static
static Applet myApplet new Hello4( )
public void windowClosing(WindowEvent event)
Hello4.myApplet.stop( ) //new
Hello4.myApplet.destroy( ) //new
System.exit(0)
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Debugging (and other) output

• Applications can use System.out.println(String
  message)
• This also works for applets run from
  appletviewer, but not if they are run from a
  browser
• Applets can use showStatus(String message)
• If you do this from an application, you must
  supply an AppletContext, or you get a
  nullPointerException
• You can always use drawString( ), or better, a
  TextField

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Hello5.java
public void paint(Graphics g)
g.drawString("Hello World!", 30, 30)
showStatus("OK for applets")
System.out.println("OK for applications")
g.drawString("OK for both applets "
" and applications", 10, 50)
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The End