设置一个按钮为一个图片，不要border

        //设置一个按钮为一个图片，不要border
        ImageIcon searchIcon = ImageToolkit.loadImageIcon(/search.png");
            ImageIcon searchHoverIcon = ImageToolkit.loadImageIcon("/search_hover.png");
            ImageIcon searchPressIcon = ImageToolkit.loadImageIcon("/search_press.png");
            searchBtn = new JButton(searchIcon);
            searchBtn.setRolloverEnabled(true);
            searchBtn.setRolloverIcon(searchHoverIcon);
            searchBtn.setPressedIcon(searchPressIcon);
             searchBtn.setBorderPainted(false);
             searchBtn.setContentAreaFilled(false);
            searchBtn.setFocusable(false);
            searchBtn.setRequestFocusEnabled(false);
            searchBtn.setPreferredSize(new Dimension(18, 18));
            searchBtn.setOpaque(false);
            searchBtn.addActionListener(new ActionListener() {

                @Override
                public void actionPerformed(ActionEvent e) {
                    enterPressed();
                }

            });