Data and Expressions - Java Software Solutions: Foundations of Program Design - page 97

LISTING 2.10 continued

DISPLAY

class, which is part of the javax.swing package, and various graphics capabilities
defined in the java.awt package. Chapter 3 explores import statements further.
A class that defines an applet extends the JApplet class, as indicated in the
header line of the class declaration. This process is making use of the object-
oriented concept of inheritance, which we discussed in Chapter 1 and explore
in more detail later in the topic. Applet classes must also be declared as public .
The paint method is one of several applet methods that have particular sig-
nificance. It is invoked automatically whenever the graphic elements of the applet
need to be painted to the screen, such as when the applet is first run or when
another window that was covering it is moved.
Note that the paint method accepts a Graphics object as a parameter. A
Graphics object defines a particular graphics context with which we can interact.
The graphics context passed into an applet's paint method represents the entire
applet window. Each graphics context has its own coordinate system. In later
examples, we will have multiple components, each with its own graphics context.
A Graphics object allows us to draw various shapes using methods such as
drawRect , drawOval , drawLine , and drawString . The parameters passed to the
drawing methods specify the coordinates and sizes of the shapes to be drawn. We
explore these and other methods that draw shapes in the next section.