The following diagram shows most of the the class heirarchy of
the AWT (Abstract Windows Toolkit), which comes as part of the core
Java language (java.awt
package and sub-packages.)
The key Component
class provides the base class for all the AWT visual components
and also for the Swing components. The
class provides a very large number of public methods - see the API
description for Component.
class provides for holding instances of other component classes.
subclass, for example, provides for the top level visible
that hold various visible components.
Containers can hold other containers. The Panel
class, in particular, is used within a top level container to arrange
its sub-components, which often are also panels. An elaborate GUI
display with lots of buttons, textfields, and other components will
employ several panels and sub-panels to arrange the visible atomic
As seen in the diagram above, the basic AWT includes several atomic
components such as buttons, labels, and textfields. You can create
fairly elaborate GUI displays with these tools.
Wins Over Heavyweight
However, as mentioned in the introduction,
there are a number of limitations to these components. For example,
simply creating a subclass of Button
for a custom button that displays an icon is not practical. Java
programs before 1.2 became know for a bland, dull appearance and
The basic problem is that these components are closely tied to
so-called peer component classes written in native code for
the local operating system GUI. This means that Java portability
required a lowest-common-denominator approach in which no
visible component could provide more capability that what was available
on all platforms. This results in very limited options in how the
components can look and perform. These basic AWT components are
called heavyweight because they drag along all the peer component
A far more flexible approach is to open a heavyweight top level
class, such as a frame, and then just let Java draw all the visible
sub-components without involving any local peer components. Such
lightweight components are very flexible, especially when
combined with the more powerful event handling structure that came
with Java vers. 1.1 (event handling will be discussed in Chapter
The Swing set of classes (available in the javax.swing
and related packages) consists primarily of lightweight components.
Swing first became available as an independent set of code that
would work with version 1.1 and then was included in the standard
Java distribution for version 1.2. Swing will be discussed in more
detail in the next section.
Though there are some drawbacks to Swing
(see the next section), It is now generally
recommended that everyone switch their Java user interface design
from AWT to Swing for all serious program development for PC and
Note: In some cases, such as when
developing programs for small platforms, it can be necessary to
remain within the older AWT framework. We discuss small platform
programming in Chapter
24. See the Chapter
6: Supplements section for a brief overview of creating user
interfaces purely within the basic AWT framework.
Latest update: Oct.25, 2004