public static int hash4(int hash,Object x,Object y,Object z,Object w){
  return 0x40000000 | (hash + 7 * System.identityHashCode(x) + 11 * System.identityHashCode(y) + 13 * System.identityHashCode(z) + 17 * System.identityHashCode(w));
}

public static int hash4 ( int hash , Object x , Object y , Object z , Object w ) { return 0x40000000 | ( hash + 7 * System . identityHashCode ( x ) + 11 * System . identityHashCode ( y ) + 13 * System . identityHashCode ( z ) + 17 * System . identityHashCode ( w ) ) ; }
utility method to combine a base hash with the identity hash of one or more objects .
