Re: Enum, switch, and a null

Daniel Pitts wrote :


Yes, and the compiler tells me where they are.

I am using this enum to select which database engine is being used. I
have an abstract class which has the switch statement. It instantiates
the concrete class for the data base engine being used. The concrete
class has the correct SQL syntax for that engine to do whatever
updates/queries need to be done for the use case.

In the simplest case, such as the login, the SQL class looks like:
-------------------------------------
abstract class SQL extends DBEngineBase
{
  SQL( TransactionCommit setAutoCommit ) throws SQLException
  {
    super( setAutoCommit );
  }

  abstract void login( Data data ) throws SQLException;

  static SQL getInstance( TransactionCommit setAutoCommit ) throws
SQLException
  {
    SQL sql = null;

    switch (Database.getDBType())
    {
      case MS_SQL:
        sql = new SQL_Microsoft( setAutoCommit );
        break;
    }

    return sql;
  }
}

-------------------------------------
The SQL_Microsoft is:
-------------------------------------
class SQL_Microsoft extends SQL
{
  SQL_Microsoft( TransactionCommit setAutoCommit ) throws SQLException
  {
    super( setAutoCommit );
  }

  @Override
  void login( Data data ) throws SQLException
  {
     // bunch of code
  }
}
-------------------------------------
and to get this going, in the Command class:
-------------------------------------
SQL sql = SQL.getInstance( SQL.TransactionCommit.AUTOMATIC_COMMIT );

sql.login( data );
-------------------------------------

So the Command class does not know what DB engine is being used (nor
should it). It simply gets an instance, and the SQL class decides which
engine is to be used.

If I add a new supported database engine, all the SQL code will need to
be written for that engine. The compiler will tell me where I am
missing a case for the new enum.

If I tried to put all the SQL methods for each use case in an enum,
then the enum would need to know about each use case, and moreover I
would need hundreds of methods within the enum.

--
Wojtek :-)