public Configuration subConfig(String prefix,String keyPrefix){
  Configuration sub=new Configuration();
  addToSubConf(sub,prefix.length() > 0 ? prefix + "." + keyPrefix : keyPrefix);
  return sub;
}

public Configuration subConfig ( String prefix , String keyPrefix ) { Configuration sub = new Configuration ( ) ; addToSubConf ( sub , prefix . length ( ) > 0 ? prefix + "." + keyPrefix : keyPrefix ) ; return sub ; }
return a sub configuration from this instance that has the keys equal to either prefix . keyprefix or keyprefix . the entries of keyprefix are added first , so they are the defaults if prefix is not found .
