Java Never Ends - Absolute Java - page 1087

The Class Thread
In Java, a thread is an object of the class Thread . The normal way to program a thread
is to define a class that is a derived class of the class Thread . An object of this derived
class will be a thread that follows the programming given in the definition of the
derived (thread) class.
Where do you do the programming of a thread? The class Thread has a method
named run . The definition of the method run is the code for the thread. When the
thread is executed, the method run is executed. Of course, the method defined in the
class Thread and inherited by any derived class of Thread does not do what you want
your thread to do. So, when you define a derived class of Thread , you override the
definition of the method run to do what you want the thread to do.
In Display 19.2 , the inner class Packer is a derived class of the class Thread . The
method run for the class Packer is defined to be exactly the same as the method fill
in our previous, unresponsive GUI (Display 19.1). So, an object of the class Packer
is a thread that will do what fill does, namely draw the circles to fill up a portion of
the window.
The method actionPerformed in Display 19.2 differs from the method
actionPerformed in our older, nonresponsive program (Display 19.1) in that the
invocation of the method fill is replaced with the following:

Thread

run()

start()

Packer packerThread = new Packer( );
packerThread.start( );
This creates a new, independent thread named packerThread and starts it
processing. Whatever packerThread does, it does as an independent thread. The main
thread can then allow actionPerformed to end and the main thread will be ready to
respond to any click of the close-window button.

Display 19.2 Threaded Version of FillDemo (part 1 of 3)

1 import javax.swing.JFrame;
2 import javax.swing.JPanel;
3 import javax.swing.JButton;
4 import java.awt.BorderLayout;
5 import java.awt.FlowLayout;
6 import java.awt.Graphics;
7 import java.awt.event.ActionListener;
8 import java.awt.event.ActionEvent;

The GUI produced is identical to the
GUI produced by Display 19.1 except
that in this version the close-window
button works even while the circles are
being drawn, so you can end the GUI
early if you get bored.

9 public class ThreadedFillDemo extends JFrame implements ActionListener
10 {
11 public static final int WIDTH = 300;
12 public static final int HEIGHT = 200;
13 public static final int FILL_WIDTH = 300;
14 public static final int FILL_HEIGHT = 100;
15 public static final int CIRCLE_SIZE = 10;
16 public static final int PAUSE = 100; // milliseconds

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