question: synchronized Set < K > keySet ( ) { HashSet < K > set = new HashSet < K > ( ) ; for ( Entry < K , V > e = stack . stackNext ; e != stack ; e = e . stackNext ) { set . add ( e . key ) ; } for ( Entry < K , V > e = queue . queueNext ; e != queue ; e = e . queueNext ) { set . add ( e . key ) ; } return set ; }
target:  Get the set of keys for resident entries.