Learning Java

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 waited patiently for events to come its way and responded to the whims of the user. Now our application is going to take some initiative—HelloJava4 will blink! Here is the code for our latest version:

//file: HelloJava4.java import java.awt.*; import java.awt.event.*; import javax.swing.*; public class HelloJava4 extends JComponent implements MouseMotionListener, ActionListener, Runnable { // Coordinates for the message int messageX = 125, messageY = 95; String theMessage; JButton theButton; int colorIndex; // Current index into someColors. static Color[] someColors = { Color.black, Color.red, Color.green, Color.blue, Color.magenta }; boolean blinkState; public HelloJava4(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 ? getBackground() : currentColor( )); g.drawString(theMessage, messageX, messageY); } public void mouseDragged(MouseEvent e) { messageX = e.getX( ); messageY = e.getY( ); repaint( ); } public void mouseMoved(MouseEvent e) {} public void actionPerformed(ActionEvent e) { // Did somebody push our button? if (e.getSource( ) == ...