Doubt in Listener interface working mechanism

Code:

import java.awt.*;
import java.awt.event.*;
import java.applet.*;

/*
<applet code="AdapterDemo" width=300 height=100>
</applet>
*/

public class AdapterDemo extends Applet
{
  String str="";

  public void init()
  {  setBackground(Color.red); 
     addMouseListener(new MyMouseAdapter());
     addMouseMotionListener(new MyMouseMotionListener());
  }
     
   public void paint(Graphics g)
   {
     g.drawString(str,20,30);
   }

}

class MyMouseAdapter extends MouseAdapter
{
  AdapterDemo adapterdemo=new AdapterDemo();
  public void mouseClicked(MouseEvent me)
 { adapterdemo.showStatus("mouse clicked");   
    adapterdemo.str="mouse clicked";
    adapterdemo.repaint();
 }
}

class MyMouseMotionListener extends MouseMotionAdapter
{
   AdapterDemo adapterdemo=new AdapterDemo(); 
  public void mouseMoved(MouseEvent me)
  {
    int x,y;
    x=me.getX();
    y=me.getY();
    adapterdemo.str="mouse moved";
    adapterdemo.repaint(); 
    adapterdemo.showStatus("mouse at :"+x+","+y);
  }
}

Why this code generated runtime error/exceptions.Is it always necessery to pass event generator object reference to the Event Listener class through 'this',as a parameter in the event registration method?
like addMouseListener(new MyMouseAdapter(this));
addMouseMotionListener(new MyMouseMotionListener(this));