code: private int calculateHash()
     {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((id == null) ? 0 : id.hashCode());
        result = prime * result + ((ownerId == null) ? 0 : ownerId.hashCode());
        result = prime * result + (getClass().getName().hashCode());
        return result;
     }
docs: Calculate the hash.
  
  @return int
  return hash