private static int hash(Object x){
  int h=x.hashCode();
  return ((h << 7) - h + (h >>> 9) + (h >>> 17));
}

private static int hash ( Object x ) { int h = x . hashCode ( ) ; return ( ( h << 7 ) - h + ( h > > > 9 ) + ( h > > > 17 ) ) ; }
return hash code for object x . since we are using power - of - two tables , it is worth the effort to improve hashcode via the same multiplicative scheme as used in identityhashmap .
