Frame/Applet Construct
Bruce Eckel, in this book, Thinking In Java
, says:
Often you'll want to be able to create a class that can be
invoked as either a window or an applet. To accomplish this,
you simply add a main() to your applet that builds an instance
of the applet inside a Frame.
Here's a simple example of what Eckel is talking about.
You can run this little gem in three different ways:
- As an applet on a web page. Just write the HTML code to load the applet
as usual and view it in a web browser.
- Using appletviewer - Run applet viewer like this:
appletviewer frameApplet.java
- At the command line - Type the following at the command line:
java frameApplet
This is the way that is probably new to you. Read on for a discussion of
what it took to make this work.
There were two methods added to the typical applet class which make it
possible for the example to function as a command line application:
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<![CDATA[
static class WL extends WindowAdapter {
public void windowClosing(WindowEvent e){
System.exit(0);
}
}
public static void main(String[] args){
frameApplet app = new frameApplet();
Frame aFrame = new Frame("frameApplet");
aFrame.addWindowListener(new WL());
aFrame.add(app, BorderLayout.CENTER);
aFrame.setSize(220,100);
app.init();
app.start();
aFrame.setVisible(true);
}
}
]]>
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The WL class is actually optional, but if you don't include it the window
which displays the applet won't close when you hit the little X in the upper
right hand corner. The main method is necessary. It first initiates an
instance of the applet class. Then it creates an instance of the Frame class
and associates it with the WL class. It then displays the applet and calls a
couple of the applet methods. You can inspect the code to figure out exactly
how it all works.
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Assignment:
Use the method demonstrated in this lesson to create an applet with a solid
red background and six yellow circles arranged in a two by three pattern. In
each circle place the name of a state (for instance, Pennsylvania) in black.
Be prepared to demonstrate the three ways it can be displayed.