private final void addUser(String channel,User user){
  channel=channel.toLowerCase();
synchronized (_channels) {
    Hashtable<User,User> users=_channels.get(channel);
    if (users == null) {
      users=new Hashtable<User,User>();
      _channels.put(channel,users);
    }
    users.put(user,user);
  }
}

private final void addUser ( String channel , User user ) { channel = channel . toLowerCase ( ) ; synchronized ( _channels ) { Hashtable < User , User > users = _channels . get ( channel ) ; if ( users == null ) { users = new Hashtable < User , User > ( ) ; _channels . put ( channel , users ) ; } users . put ( user , user ) ; } }
add a user to the specified channel in our memory . overwrite the existing entry if it exists .
