Doing commerce on the Web is the ultimate object-oriented problem," says Virtual Vineyards Java programmer Rob Reesor. "We deal with real asynchronous parallel processes such as credit card authorization, and shipment of tangible products in a multicompany, multiprotocol environment. Reesor offers this method, which takes a vector of components and returns a vector of the part numbers needed to make up those components.

/*
 * For example, one component may be Widget 4 and 
 * another may be Widget 5. The parts needed for 
 * Widget 4 may be parts 1, 3, 7, 8, 13 and the 
 * parts needed for Widget 5 may be 2, 5, 7, 8, 12. 
 * The part numbers needed for both
 * are 1, 2, 3, 5, 7, 8, 12, 13.
 * 
 * This parts list could be used to notify vendors to
 * gear up production.
 */
private Vector partsList(Vector components)
{
  // We need an Enumeration of the elements of 
  // components, a Hashtable to make it easy to 
  // avoid duplication, and a Vector to return.
  Enumeration enum = components.elements();
  Hashtable partsHash = new Hashtable();
  Vector partsList = new Vector();
 
  // HandyInfo is an object that is created when the 
  // server starts up and contains a cache of handy 
  // information about components.
  nc.gendatabase.HandyInfo hi = 
    new nc.gendatabase.HandyInfo(self);
 
  // We loop through the components getting the int 
  // value for each. We use HandyInfo to get the 
  // information about the components so we can get 
  // a Vector of it's parts list.
  while (enum.hasMoreElements())
  {
    int comp = 
      ((Integer)enum.nextElement()).intValue();
    Vector parts = null;
 
    hi.getInfoForComponent(comp);
    parts = hi.getParts(comp);
 
    // We create an Enumeration of the parst of 
    // this component. We loop through the enumeration 
    // using each part number as a Hashtable key. 
    // Since components may share part numbers, we 
    // can't just return a Vector of all part numbers
    // of all components. Keying into a  Hashtable will 
    // result in no duplication.
    Enumeration partsEnum = parts.elements();
 
    while (partsEnum.hasMoreElements())
    {
      charsHash.put(
        (Integer)partsEnum.nextElement(), "1");
    }
  }
 
  // Finally, we loop over the keys of the Hashtable to 
  // create the Vector of part numbers to return.
  enum = partsHash.keys();
 
  while (enum.hasMoreElements())
  {
    partsList.addElement((Integer)enum.nextElement());
  }
 
  return partsList;
}

Release No Website Before Its Time--an Interview with Rob Reesor and Ed Videki of Virtual Vineyards

What do asynchronous, parallel processes, and selling wine have in common? Read this article for the answer.