This page contains an archived post to the Java Answers Forum made prior to February 25, 2002. If you wish to participate in discussions, please visit the new Artima Forums.

Message:

Factories

Posted by Matt Gerrans on January 23, 2002 at 3:36 AM

Just a point on nomenclature.

Maybe I don't understand exactly what you are saying here, but usually a factory only creates objects that are used by the system. These objects are all based on some abstract base class or interface, of course. The factory itself is not the base class, however. At runtime, based on whatever criteria is relevant, the factory instantiates and returns instances of derived objects which have the appropriate implementation.

> Well, I have been there once. We moved from Oracle to MS SQL and believe me its a nightmare of unimaginable magnitude! Oracle does not support TOP keyword, calling stored procedures is different, what not.

> So, I proppsed a design and my boss kinda likes it. Thought I'd share and argue.

> To sum up, its a mix of Singleton and Abstract Factory.

> I have an interface SQLFactory which has a bunch of methods that promise a certain behaviour. For example,

>

> public interface SQLFactory
> {
>     public string getPassword(String userID);
>     //and a few more ...
> }
> 

> Now I have classes that implement this interface, specific to a database vendor. For example,
>

> public class OracleSQLFactory implements SQLFactory
> {
>     public String getPassword(String userID)
>     {
>         //get connection from a pool.
>         //call stored procedure or execute SQL statement.
>         //heres where Oracle is different from MS SQL (to me anyways)
>         //return passwordForThisUserID.
>     }
> }
> 

> And another class, MSSQLFactory which has statements specific to MS SQL.

> Now all this is of no good with out this last part. create a reference of SQLFactory which can be accessed through out the application.
> and 'take care' that at any point of time this reference refers to just one of the implementing classes (obviously it depends on the database in use.)

> Now, all calls will be made to this reference. So, one who concentrates on business logic, is happy with the promise of interface and doesnt need to care about database calls or whatever.

> So to move to IBM DB2, I just need to implement SQLFactory thingee and I am happy. Take a step further and create this instance at runtime.

>
> Note that if the application changes, interface changes too.
>

• abstract factories Chin Loong January 23, 2002 at 6:03 AM (4)
  • Database migration Jay January 23, 2002 at 5:14 PM (2)
    • Comments anyone? ...EOM Jay January 25, 2002 at 1:47 PM (1)
      • Abstract Factories vs. Abstract Methods Matt Gerrans January 25, 2002 at 5:12 PM (0)
  • important! Chin Loong January 23, 2002 at 6:05 AM (0)