Learning Java, 4th Edition

HelloJava4: Netscape’s Revenge

We have explored quite a few features of Java with the first three versions of the HelloJava application. But until now, our application has been rather passive; it has been completely event-driven, waiting patiently for events to come its way and responding to the whims of the user. Now our application is going to take some initiative—HelloJava4 will blink!^[5] Here is the code for our latest version:

    //file: HelloJava4.java
    import java.awt.*;
    import java.awt.event.*;
    import javax.swing.*;

    public class HelloJava4
    {
      public static void main( String[] args ) {
        JFrame frame = new JFrame( "HelloJava4" );
        frame.add( new HelloComponent4("Hello, Java!") );
        frame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
        frame.setSize( 300, 300 );
        frame.setVisible( true );
      }
    }

    class HelloComponent4 extends JComponent
        implements MouseMotionListener, ActionListener, Runnable
    {
      String theMessage;
      int messageX = 125, messageY = 95; // Coordinates of the message

      JButton theButton;

      int colorIndex; // Current index into someColors.
      static Color[] someColors = {
        Color.black, Color.red, Color.green, Color.blue, Color.magenta };

      boolean blinkState;


      public HelloComponent4( String message ) {
        theMessage = message;
        theButton = new JButton("Change Color");
        setLayout( new FlowLayout() );
        add( theButton );
        theButton.addActionListener( this );
        addMouseMotionListener( this );
        Thread t = new Thread( this );
        t.start();
      }

      public void paintComponent( Graphics g ) {
        g.setColor(blinkState ...