Drag and drop, adn repaint to have the bachground cleaned

Hi, I am dragging and dropping JButtons, but when I do, it leaves it's mark (or shadow behind). How can I do to have a clean blackground?

Here's my code, I'm usig 2 classes. The first class is Appletprueba, and it calls a second class (applet que se draga), which contains the button that can be dragged..

Thnaks in advance.

package proyectoreal;

import java.awt.*;

//import java.awt.event.*;

//import java.applet.*;

//import com.borland.jbcl.layout.*;

import javax.swing.*;

import java.awt.event.*;

//import javax.swing.border.*;

class botonquesedragaextends JButton{

public botonquesedraga(){

try{

jbInit();

}

catch(Exception e){

e.printStackTrace();

}

privatevoid jbInit()throws Exception{

this.setBackground(Color.pink);

this.addMouseMotionListener(new botonquesedraga_this_mouseMotionAdapter(this));

}

void this_mouseDragged(MouseEvent e){

this.setLocation(this.getX()+e.getX(),this.getY()+e.getY());

this.repaint();

this.validate();

}

class botonquesedraga_this_mouseMotionAdapterextends java.awt.event.MouseMotionAdapter{

botonquesedraga adaptee;

botonquesedraga_this_mouseMotionAdapter(botonquesedraga adaptee){

this.adaptee = adaptee;

}

publicvoid mouseDragged(MouseEvent e){

adaptee.this_mouseDragged(e);

}

Here is the other class. Thanks