public String toString(){
  StringBuilder s=new StringBuilder();
  for (  String key : this)   s.append(key + " ");
  if (s.length() > 0)   s.deleteCharAt(s.length() - 1);
  return s.toString();
}

public String toString ( ) { StringBuilder s = new StringBuilder ( ) ; for ( String key : this ) s . append ( key + " " ) ; if ( s . length ( ) > 0 ) s . deleteCharAt ( s . length ( ) - 1 ) ; return s . toString ( ) ; }
returns a string representation of this set .
