JToolBarに配置したアイコンをドラッグして並べ替える

class DragHandler extends MouseAdapter {
  private final JWindow window = new JWindow();
  private Component draggingComponent = null;
  private int index = -1;
  private Component gap = Box.createHorizontalStrut(24);
  private Point startPt = null;
  private int gestureMotionThreshold = DragSource.getDragThreshold();
  public DragHandler() {
    window.setBackground(new Color(0x0, true));
  }

  @Override public void mousePressed(MouseEvent e) {
    JComponent parent = (JComponent) e.getComponent();
    if (parent.getComponentCount() <= 1) {
      startPt = null;
      return;
    }
    startPt = e.getPoint();
  }

  @Override public void mouseDragged(MouseEvent e) {
    Point pt = e.getPoint();
    JComponent parent = (JComponent) e.getComponent();
    if (startPt != null && startPt.distance(pt) > gestureMotionThreshold) {
      startPt = null;
      Component c = parent.getComponentAt(pt);
      index = parent.getComponentZOrder(c);
      if (c == parent || index < 0) {
        return;
      }
      draggingComponent = c;

      parent.remove(draggingComponent);
      parent.add(gap, index);
      parent.revalidate();
      parent.repaint();

      window.add(draggingComponent);
      window.pack();

      Dimension d = draggingComponent.getPreferredSize();
      Point p = new Point(pt.x - d.width / 2, pt.y - d.height / 2);
      SwingUtilities.convertPointToScreen(p, parent);
      window.setLocation(p);
      window.setVisible(true);

      return;
    }
    if (!window.isVisible() || draggingComponent == null) {
      return;
    }

    Dimension d = draggingComponent.getPreferredSize();
    Point p = new Point(pt.x - d.width / 2, pt.y - d.height / 2);
    SwingUtilities.convertPointToScreen(p, parent);
    window.setLocation(p);

    for (int i = 0; i < parent.getComponentCount(); i++) {
      Component c = parent.getComponent(i);
      Rectangle r = c.getBounds();
      Rectangle r1 = new Rectangle(r.x, r.y, r.width / 2, r.height);
      Rectangle r2 = new Rectangle(r.x + r.width / 2, r.y, r.width / 2, r.height);
      if (r1.contains(pt)) {
        if (c == gap) {
          return;
        }
        int n = i - 1 >= 0 ? i : 0;
        parent.remove(gap);
        parent.add(gap, n);
        parent.revalidate();
        parent.repaint();
        return;
      } else if (r2.contains(pt)) {
        if (c == gap) {
          return;
        }
        parent.remove(gap);
        parent.add(gap, i);
        parent.revalidate();
        parent.repaint();
        return;
      }
    }
    parent.remove(gap);
    parent.revalidate();
    parent.repaint();
  }

  @Override public void mouseReleased(MouseEvent e) {
    startPt = null;
    if (!window.isVisible() || draggingComponent == null) {
      return;
    }
    Point pt = e.getPoint();
    JComponent parent = (JComponent) e.getComponent();

    Component cmp = draggingComponent;
    draggingComponent = null;
    window.setVisible(false);

    for (int i = 0; i < parent.getComponentCount(); i++) {
      Component c = parent.getComponent(i);
      Rectangle r = c.getBounds();
      Rectangle r1 = new Rectangle(r.x, r.y, r.width / 2, r.height);
      Rectangle r2 = new Rectangle(r.x + r.width / 2, r.y, r.width / 2, r.height);
      if (r1.contains(pt)) {
        int n = i - 1 >= 0 ? i : 0;
        parent.remove(gap);
        parent.add(cmp, n);
        parent.revalidate();
        parent.repaint();
        return;
      } else if (r2.contains(pt)) {
        parent.remove(gap);
        parent.add(cmp, i);
        parent.revalidate();
        parent.repaint();
        return;
      }
    }
    if (parent.getBounds().contains(pt)) {
      parent.remove(gap);
      parent.add(cmp);
    } else {
      parent.remove(gap);
      parent.add(cmp, index);
    }
    parent.revalidate();
    parent.repaint();
  }
}