Just one:
public void paint ( Graphics gr )
(However, the class inherits many more methods
from class JApplet
.)
JApplet
Class// X -- notice the 'x' in javax import javax.swing.JApplet; import java.awt.*; public class JustOneCircle extends JApplet { final int radius = 25; public void paint ( Graphics gr ) { gr.setColor( Color.white ); gr.fillRect( 0, 0, 150, 150 ); gr.setColor( Color.black ); gr.drawOval( (150/2 - radius), (150/2 - radius), radius*2, radius*2 ); } }
The definition of JApplet
provides a framework
for building an applet.
By itself, the class JApplet
does little that is visible in
the Web browser.
(It does a great many things behind the scenes, however.)
To build upon this framework, you
import
javax.swing.JApplet
and
extend
the JApplet
class.
When you extend a class, you are making a new class by
building upon a base class.
This example defines a new class called JustOneCircle
.
The new class has everything in it that the class JApplet
has.
(This is called inheritance.
Inheritance is discussed at greater length in chapter 50.)
The class JApplet
has a paint()
method,
but that method does little.
Objects of class
JustOneCircle
have their own
paint()
method because the definition in JustOneCircle.java
overrides the one in JApplet
.
The Web browser calls the paint()
method when it needs to "paint"
the section of the monitor screen devoted to an applet.
Each applet that you write
has its own paint()
method.
The paint()
method contains the statement
gr.drawOval( (150/2 - radius), (150/2 - radius), radius*2, radius*2 );
What do you suppose that this does? (Ignore the details.)