public static void main(String[] args) {
 JFrame frame = new JFrame();
 JDesktopPane desktopPane = new JDesktopPane();
 frame.setContentPane(desktopPane);

 for(int i = 0; i < 8; i++) {
  JPanel panel = new JPanel();
  panel.setBackground(Color.blue);
  panel.setSize(100, 100);
  DragHandler handler = new DragHandler(panel);
  desktopPane.add(panel);
 }
 frame.pack();
 frame.setVisible(true);
}

static class DragHandler extends MouseInputAdapter {

 int x0, y0, x, y;
 JComponent comp;
 Rectangle rw = new Rectangle();

 public DragHandler(JComponent comp) {
  this.comp = comp;
  comp.addMouseListener(this);
  comp.addMouseMotionListener(this);
 }

 public void mousePressed(MouseEvent e) {
  x = e.getX();
  y = e.getY();
  Point p = new Point(x, y);
  SwingUtilities.convertPointToScreen(p, e.getComponent());
  x = p.x;
  y = p.y;

  x0 = comp.getX();
  y0 = comp.getY();
 }

 public void mouseReleased(MouseEvent e) {
 }

 public void mouseDragged(MouseEvent e) {
  Point p = e.getPoint();
  SwingUtilities.convertPointToScreen(p, e.getComponent());
  int dx = x - p.x;
  int dy = y - p.y;
  rw = comp.getBounds(rw);
  rw.x = x0 - dx;
  rw.y = y0 - dy;

  comp.setLocation(rw.x, rw.y);
 }
}

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