Widgets (Components)
Example Code (adapted from example by David Matuszek, UPenn) |
Components (also known as widgets) are the various user controls and displays provided by the Java AWT; they are the basic building blocks of a Graphical User Interface. The following illustration shows the most common AWT components:
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This is a "live" applet, not just a picture of an applet
(try it!). Each of the components in the above applet, when manipulated, places
a message in the status line of the applet (in the above illustration, the status
line contains the text Applet started.
) When you run the applet
with appletviewer
, the status line is shown at the bottom of the
applet; when you run the applet in a browser, the status line is usually shown
at the bottom of the browser window (although some browsers may not show the
status line at all).
The code for this applet illustrates:
We recommend that you download the source code for the above applet and keep it handy. When you want to use a particular kind of component, you can use this code as a model for how to create the component and handle the events that it generates.
There are two versions of the source code for this applet:
Widgets.java uses anonymous inner classes; complete BlueJ package is in WidgetsAnonymous.zip.
Widgets2.java uses member classes; complete BlueJ package is in WidgetsMembers.zip.
In general, member classes are easier to understand, while anonymous inner classes are more convenient.
Note: a .jar
file is just like a .zip
file, and you
can use WinZip or equivalent to unpack it.