paint(Graphics g, JComponent c)方法中参数C如何使用?

我用paint(Graphics g, JComponent c)方法绘制报表表头,编译时提示:未使用参数C
运行时表头无法显示且提示:UIDefaults.getUI() failed: no ComponentUI class     for: ...
java.lang.Error ...
请问:参数C的作用,如何修改这段代码?谢谢!（注:代码来自http://www.54bk.com/?uid-776-action-viewspace-itemid-30520）  
           public static ComponentUI createUI(JComponent c) {      
        return new GroupableTableHeaderUI();
       }
 public void paint(Graphics g, JComponent c) {         //提示:未使用参数C    TableColumnModel cm = header.getColumnModel();
 if (cm.getColumnCount() > 0) {
    
            Rectangle clip = g.getClipBounds();
            Point left = clip.getLocation();
            Point right = new Point(clip.x + clip.width - 1, clip.y);
            int cMin = header.columnAtPoint(left);
            int cMax = header.columnAtPoint(right);
            if (cMax == -1) {
                            cMax = cm.getColumnCount() - 1;
                             }
 int columnWidth;
            Rectangle cellRect = header.getHeaderRect(cMin);            Set done = new HashSet();
 for (int column = cMin; column <= cMax; column++) {
                TableColumn aColumn = cm.getColumn(column);
                columnWidth = aColumn.getWidth();
                cellRect.width = columnWidth;
                paintCell(done, g, cellRect, column);
                cellRect.x += columnWidth;
            }
rendererPane.removeAll();
        }
    }