Java Reference
In-Depth Information
addition to a title bar and a border, it provides a wealth of other facilities. Its superclasses are shown in
Fig-
The
Component
class is the grandmother of all component classes — it defines the basic properties and
methods shared by all components. You see later that all the Swing components have the
Component
class as
a base. The
Container
class adds the capability for a
Component
object to contain other components, which
is a frequent requirement. Because
JFrame
has
Container
as a superclass, a
JFrame
object can contain other
components. Beyond the obvious need for a window to be able to contain the components that represent the
GUI, a menu bar should contain menus, for example, which in turn contains menu items; a toolbar obviously
contains toolbar buttons; and there are many other examples. For this reason the
Container
class is also a
base for all the classes that define Swing components.
The
Window
class adds methods to the
Container
class that are specific to a window, such as the capab-
ility to handle events arising from user interaction with the window. The
Frame
class is the original class in
java.awt
that provided a proper window with a title bar and a border, with which everyone is familiar. The
JFrame
class adds functionality to the
Frame
class to support much more sophisticated facilities for drawing
and displaying other components. You can deduce from the hierarchy in the diagram how a
JFrame
object
can easily end up with its 200+ methods, as it has five superclasses from which it inherits members. You
aren't going to trawl through all these classes and methods. You just look into the ones you need in context
as you go along, and then see how they are applied in some examples. This teaches you the most important
methods in this class.
Framing a Window
You can display an application window simply by creating an object of type
JFrame
, calling a method for
the object to set the size of the window, and then calling a method to display the window. Executing the
following code fragment creates a window object and displays the window that it represents:
