Channels

gistfile1.java

public interface ChannelReciever {
  public void sendMessage(String message);
}

public interface ChannelFormatter {
  public String formatMessage(ChannelReciever member, String message);
}

public interface Channel {
  String getChannelName();
  String sendMessage(String message);
  void addMember(ChannelReceiver member);
  void removeMember(ChannelReceiver member);
  List<ChannelReceiver> getMembers();
  void setFormatter(ChannelFormater formatter);
  ChannelFormater getFormatter(); 
}

public interface ChannelFilter {
  Channel selectChannel(ChannelReceiver member, MultiChannel multiChannel);
}

public interface MultiChannel {
  void registerChannel(Channel channel, int priority);
  int getPriority(Channel channel);
  List<Channel> getRegisteredChannels();
}

removeMember should probably be boolean.
i gather MultiChannel would than be per User?