Extending the JApplet Class

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.

//         X -- notice the 'x' in javax
import javax.swing.JApplet;
import java.awt.*;

public class Poem extends JApplet
{
  public void paint ( Graphics gr )
  { 
    setBackground( Color.white );
    gr.drawString("Loveliest of trees, the cherry now", 25, 30);
    gr.drawString("Is hung with bloom along the bough,", 25, 50);
    gr.drawString("And stands about the woodland ride", 25, 70 );
    gr.drawString("Wearing white for Eastertide." ,25, 90);
    gr.drawString("--- A. E. Housman" ,50, 130);
   }
}

When you extend a class, you are making a new class by building upon a base class. This example defines a new class called Poem. 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 Poem have their own paint() method because the definition in Poem.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.