I'm trying to develop a Java client for an on-line game.  One screen of
the client is supposed to show a list of available games,  and allow the
user to select one,  then join it or watch it.  I decided to do this using
a JTable.  The first few columns display data about the prospective game;
I want the last column to display two buttons,  one of which would perform
the action of joining a game.  Accordingly,  I wrote my own table model.
getColumnClass() on the last column of the table returns GameInfo.class.
When I create the table,  I also do

                    games_table.setDefaultRenderer(GameInfo.class,
                                                   model.suitableRenderer());

where model.suitableRenderer returns an instance of the following class:

  class LoginColumnRenderer implements javax.swing.table.TableCellRenderer {
     public java.awt.Component getTableCellRendererComponent(JTable table,
                                              Object value,
                                              boolean isSelected,
                                              boolean hasFocus,
                                              int row, int column) {
        if (value instanceof GameInfo) {
           return new LoginColumnRendererComponent((GameInfo)value);
        } else {
           throw new java.lang.IllegalArgumentException("Not a Game");
        }
     }
  }

getTableCellRendererComponent(),  in turn,  returns an instance of the
following class:

  class LoginColumnRendererComponent extends java.awt.Container
                                     implements java.awt.event.ActionListener {
     java.awt.Button b_watch;
     java.awt.Button b_join;
     
     GameInfo game;
     
     LoginColumnRendererComponent(GameInfo g) {
        game = g;
        b_watch = new java.awt.Button("watch");        
        b_join  = new java.awt.Button("join");
    add(b_watch);
    add(b_join);
    invalidate();
    validate();
     }
     
     public void actionPerformed(java.awt.event.ActionEvent evt) {
        if (evt.getSource()==b_watch) {
           lj.watchGame(game);
        } else if (evt.getSource()==b_join) {
           lj.joinGame(game);
        }
  }

My problem is that the buttons don't show up.  Instead,  that particular
column of the table is just blank.  What am I doing wrong?