🚀 go-pugleaf

I have another piece of code that is acting funny which I don't understand.

After I run this code in the IDE, after a few moments (five to ten seconds),
I get a copy of the Exit button at the top of the screen and I have no idea
why it's doing that.  Any ideas?

The code simple is in the preliminary stages of getting a string to follow a
sine wave, but there are some basic issues I'm working through first (as you
can very well tell :>).  And as I mentioned, I can't for the life of me
figure out why I'm getting a dupe of the Exit button at the top of the
frame, but it's not live.
------------------------------------------------------------
import java.awt.*;
import javax.swing.*;
import javax.swing.event.*;
import java.awt.event.*;
import java.lang.InterruptedException;

public class DrawSineWave {
   public DrawSineWave(){

   }

   public static void main( String args[] ){
      DrawSineWaveFrame f = new DrawSineWaveFrame();
      f.addWindowListener( new WindowAdapter(){
         public void windowClosing( WindowEvent e ){
            System.exit( 0 );
         }
      });
      f.show();
   }
}

class DrawSineWaveFrame extends JFrame{
   public DrawSineWaveFrame(){
      super( "DrawSineWaveTitle Goes Here" );


      JButton exit = new JButton( "Exit" );
      exit.addActionListener( new ActionListener(){
         public void actionPerformed( ActionEvent e ){
            System.exit( 0 );
         }
      });

      Container c = this.getContentPane();
      c.add( exit, BorderLayout.SOUTH );

      DrawSineWavePanel p = new DrawSineWavePanel();
      setSize( 800, 600 );
      getContentPane().add( p );
   }
}

class DrawSineWavePanel extends JPanel{
   final int UNITS = 5;

   private double x = 0;
   private double y = 0;
   private Dimension panelSize;
   DrawMe drawMe;

   public DrawSineWavePanel(){
      super();
      drawMe = new DrawMe( this );
      drawMe.start();
   }

   public void paintComponent( Graphics g ){
      g.translate( UNITS, getHeight()/2);
      g.setColor( Color.blue);
      int w = getWidth();
      int h = getHeight();
      g.drawLine( -UNITS, 0, w, 0 );
      g.drawLine( 0, (int)h/2, 0, -(int)(h/2));
      int marker = 0;
      Color markerColor = Color.red;
      //x axis
      for( int i = 0; i < w; i++ ){
         if( i % UNITS == 0 ){
            marker = 4 * UNITS;
            markerColor = Color.red;
         } else {
            marker = 2 * UNITS;
            markerColor = Color.blue;
         }
         g.setColor( markerColor);
         g.drawLine( i, marker, i, -marker );
         if( i % UNITS == 0 ) {
            g.drawString( String.valueOf( i ), i - 10, marker + 15 );
         }
         i += ( 2 * UNITS );
      }
      //-y axis
      for( int i = 0; i < h; i++) {
         if( i % UNITS == 0 ){
            marker = 4 * UNITS;
            markerColor = Color.red;
         } else {
            marker = 2 * UNITS;
            markerColor = Color.blue;
         }
         g.setColor( markerColor);
         g.drawLine( marker, i, -marker, i );
         if( i % UNITS == 0 ) {
            g.drawString( String.valueOf( i ), marker + 15, i - 10 );
         }
         i += ( 2 * UNITS );
      }
   }
}

class DrawMe extends Thread{
   final int UNITS = 5;
   private Graphics g;
   private int x;
   private int y;
   JPanel pp;
   public DrawMe( DrawSineWavePanel p ){
      super( "drawme" );
      pp = p;
      x = (int)p.getWidth() + 10;
      y = (int)p.getHeight() / 2;

   }

   public void run(){
      try{
         for(;;){
            g = pp.getGraphics();
            if( g != null ){
               if( x > pp.getWidth() ) {
                  x = 5 * UNITS;
                  y += ( 5 * UNITS );
               }
               g.drawString( "Trying this out", x, y);
               x += UNITS;
               sleep( 250 );
               pp.repaint();
            }
         }// for
      }
      catch( InterruptedException ie ){
         System.err.println("FORCED to stop the this thread");
         ie.printStackTrace();
      }
      System.err.println("DONE the thread looping, about to exit");
   }
}