Introduction
The Java programming language
class library provides a user interface toolkit called Abstract Windowing
Toolkit or AWT. AWT is powerful and flexible. Newcomers, however, often find
their power veiled. Descriptions of classes and methods found in distributed
documentation provide little guidance to the new programmer. In addition, the
available examples often leave many important questions unanswered. Of course,
newcomers should expect some difficulty. Effective graphical user interfaces
are inherently challenging to design and implement, and the sometimes complicated
interactions between classes in AWT only make this task more complex. However,
with proper guidance, creating a graphical user interface using AWT is not only
possible but relatively simple.
This article discusses some of
the philosophies behind AWT and addresses the practical concern of how to
create a simple user interface for an applet or application
What
is a user interface
The user interface is the part of
a program that interacts with the user of the program. User interfaces take
several forms. These forms vary in complexity, from simple command-line
interfaces to the point-and-click graphical user interfaces provided by many
modern applications.
At the lowest level, the
operating system transmits mouse and keyboard information to the program as
input and provides pixels for program output. The AWT is designed so that
programmers do not worry about the details of tracking the mouse or reading the
keyboard, or attending to the details of recording on the screen. AWT provides
a well-designed object-oriented interface for these services and low-level
resources.
Components
and containers
Creating
a container
The Java programming language
class library provides a user interface toolkit called Abstract Windowing
Toolkit or AWT. AWT is powerful and flexible. Newcomers, however, often find
their power veiled. Descriptions of classes and methods found in distributed
documentation provide little guidance to the new programmer. In addition, the
available examples often leave many important questions unanswered. Of course,
newcomers should expect some difficulty. Effective graphical user interfaces
are inherently challenging to design and implement, and the sometimes complicated
interactions between classes in AWT only make this task more complex. However,
with proper guidance, creating a graphical user interface using AWT is not only
possible but relatively simple.
This article discusses some of
the philosophies behind AWT and addresses the practical concern of how to
create a simple user interface for an applet or application
What
is a user interface
The user interface is the part of
a program that interacts with the user of the program. User interfaces take
several forms. These forms vary in complexity, from simple command-line
interfaces to the point-and-click graphical user interfaces provided by many
modern applications.
At the lowest level, the
operating system transmits mouse and keyboard information to the program as
input and provides pixels for program output. The AWT is designed so that
programmers do not worry about the details of tracking the mouse or reading the
keyboard, or attending to the details of recording on the screen. AWT provides
a well-designed object-oriented interface for these services and low-level
resources.
Since the Java programming language is independent of the platform, the AWT must also be independent of the platform. The AWT is designed to provide a common set of graphical user interface design tools that work across multiple platforms. The user interface elements provided by AWT are implemented using the native GUI toolkit of each platform, thus preserving the appearance of each platform. This is one of the strongest points of AWT. The disadvantage of this approach is the fact that a graphical user interface designed on one platform may look different when it is displayed on another platform.
Components
and containers
A graphical user
interface is constructed of graphic elements called components. Typical
components include elements such as buttons, scroll bars, and text fields. The
components allow the user to interact with the program and provide the user
with visual feedback on the status of the program. In the AWT, all the
components of the user interface are instances of the Component class or one of
its subtypes.
The components are not
alone, but they are in containers. The containers contain and control the
design of the components. The containers are themselves components and,
therefore, can be placed inside other containers. In the AWT, all containers
are instances of the Container class or one of its subtypes.
Creating
a container
Before adding the components that make up a user
interface, the programmer must create a container. When building an
application, the programmer must first create an instance of the Window class
or the Frame class. When creating an applet, a framework already exists (the
browser window). Since the Applet class is a subtype of the Panel class, the
programmer can add the components to the instance of the Applet class itself.
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