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