combobox 上添加控件 问题， 急，帮帮忙

Question

小弟在ComboBox上想加个按钮，挡住右边的图，用this.add(button,-1),为什么总加在左边，换了几个参数也不行啊。帮帮忙急急急public void setComboBoxState()
{
imageSource = new String[5];

imageSource[0] = "/image/ContentTextoperate_date_click.gif";
imageSource[1] = "/image/ContentTextoperate_date_default.gif";
imageSource[2] = "/image/ContentTextoperate_date_disable.gif";
imageSource[3] = "/image/ContentTextoperate_date_hover.gif";
imageSource[4] = "/image/ContentTextoperate_date_visited.gif";


imageMatch = new ImageIcon[5];

imageMatch[0] = new ImageIcon(getClass().getResource(imageSource[0].toString()));
imageMatch[1] = new ImageIcon(getClass().getResource(imageSource[1].toString()));
imageMatch[2] = new ImageIcon(getClass().getResource(imageSource[2].toString()));
imageMatch[3] = new ImageIcon(getClass().getResource(imageSource[3].toString()));
imageMatch[4] = new ImageIcon(getClass().getResource(imageSource[4].toString()));

    this.setSize(280, 19);
    Width = 280 ;
    Hight = 19 ;
    this.setComboBoxBorder(true);
    this.setBackground(new Color(255,255,255));
    this.setForeground(new Color(255,255,255));
    


  JButton button = new JButton();
  button.setIcon(imageMatch[1]);
  button.setPressedIcon(imageMatch[0]);
  button.setDisabledIcon(imageMatch[2]);
  button.setRolloverIcon(imageMatch[3]);
  button.setSelectedIcon(imageMatch[4]);
  button.setSize(imageMatch[0].getIconWidth()+1, imageMatch[0].getIconHeight()+1);
//    this.add(button,-1);
     }