public boolean contains(String key)
Returns true if the bundle contains the named key.

 public String format(String key,
    Object args)
Convienience for accessing a formatter and formatting a localized message with arguments.

 public String get(String key)
Returns the localized message for the given key. If catalog does not contain such a key, then a modified version
of the key is returned (converted to upper case and enclosed in brackets).

 public MessageFormatter getFormatter(String key)
Returns a formatter for the message, which can be used to substitute arguments (as per java.util.Formatter ).