Learning Java, 4th Edition

HelloJava3: The Button Strikes!

Now we can move on to some fun stuff. HelloJava3 brings us a new graphical interface component: JButton.^[4] In this example, we add a JButton component to our application that changes the color of our text each time the button is pressed. The draggable-message capability is still there, too. Our new code looks like this:

    //file: HelloJava3.java
    import java.awt.*;
    import java.awt.event.*;
    import javax.swing.*;

    public class HelloJava3
    {

      public static void main( String[] args ) {
        JFrame frame = new JFrame( "HelloJava3" );
        frame.add( new HelloComponent3("Hello, Java!") );
        frame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
        frame.setSize( 300, 300 );
        frame.setVisible( true );
      }
    }

    class HelloComponent3 extends JComponent
        implements MouseMotionListener, ActionListener
    {
      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 };

      public HelloComponent3( String message ) {
        theMessage = message;
        theButton = new JButton("Change Color");
        setLayout( new FlowLayout() );
        add( theButton );
        theButton.addActionListener( this );
        addMouseMotionListener( this );
      }

      public void paintComponent( Graphics g ) {
        g.drawString( theMessage, messageX, messageY );
      }

      public void mouseDragged( MouseEvent e ) {
        messageX = e.getX();
        messageY = e.getY();
        repaint();
      }

      public void mouseMoved( MouseEvent ...