public Set<String> keySet(){
  HashSet<String> set=new HashSet<String>();
  set.addAll(container.keySet());
  set.addAll(cache.keySet());
  return set;
}

public Set < String > keySet ( ) { HashSet < String > set = new HashSet < String > ( ) ; set . addAll ( container . keySet ( ) ) ; set . addAll ( cache . keySet ( ) ) ; return set ; }
returns the keysets of both the container and cache hashmaps
