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18. The java.awt Package

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The java.awt package is the Abstract Windowing Toolkit. The classes of this package may be roughly divided into three categories (see Figure 18.1 and Figure 18.2).

Note that separate packages, java.awt.datatransfer, java.awt.event, and java.awt.image, contain classes for cut-and-paste, event handling, and image manipulation.

Figure 18.1: Graphics, event, and exception classes of the java.awt package

[Graphic: Figure 18-1]

In the first category of classes, Graphics is probably the most important. This class defines methods for doing line and text drawing and image painting. It relies on other classes such as Color, Font, Image, and Polygon. Image is itself an important class, used in many places in java.awt and throughout the related package java.awt.image. Event is another important class that describes a user or window system event that has occurred. In Java 1.1, Event is superseded by the AWTEvent class.

Component and MenuComponent are root classes in the second category of java.awt classes. Their subclasses are GUI components that can appear in interfaces and menus. The Container class is one that contains components and arranges them visually. You add components to a container with the add() method and specify a layout manager for the container with the setLayout() method.

There are three commonly used Container subclasses. Frame is a toplevel window that can contain a menu bar and have a custom cursor and an icon. Dialog is a dialog window. Panel is a container that does not have its own window--it is contained within some other container.

The third category of java.awt classes is the layout managers. The subclasses of LayoutManager are responsible for arranging the Component objects contained within a specified Container. GridBagLayout, BorderLayout, and GridLayout are probably the most useful of these layout managers.

See Chapter 8, New AWT Features, for examples of using some of the new Java 1.1 features of this package.

Figure 18.2: Component and layout classes of the java.awt package

[Graphic: Figure 18-2]

18.1 java.awt.AWTError (JDK 1.0)

Signals that an error has occurred in the java.awt package.

public class AWTError extends Error {
    // Public Constructor
            public AWTError(String msg);
}

Hierarchy:

Object->Throwable(Serializable)->Error->AWTError


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