Re: Enum, switch, and a null

 Daniel Pitts <>
Mon, 10 Sep 2007 23:59:16 -0000
On Sep 10, 4:42 pm, Wojtek <> wrote:

Lew wrote :

Wojtek wrote:

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

   return sql;

Another approach is to instantiate a Map <DBType, SQL> to retrieve the
desired SQL (or a Class<? extends SQL>), instantiated from a descriptor or
other resource.

SQL sql = dbMap.get( Database.getDBType() );

So then the get would return an already instantiated class? What about
threading? Would not all threads then get the same instance?

This is part of a Web app. Lots of threads...

Or is dbMap created for each use. That means I would be creating an
extra object (the map), plus an extra object for each DB engine, but
only using one of the engines for the life of the app.

Wojtek :-)

Hey, use Hibernate, that'll solve all your problems! :-)

If you change your DBType enum to be an interface or class with the a
abstract SQL getSQLInstance(TransactionCommit setAutoCommit);

class MS_SQL_DBType implements DBType {
  public SQL getSQLInstance(TransactionCommit setAutoCommit)
    return new SQL_Microsoft( setAutoCommit );

class MySQL_DBType implements DBType {
  public SQL getSQLInstance(TransactionCommit setAutoCommit)
    return new SQL_MySSQL( setAutoCommit );

etc... and so forth.

Add a method to your DBType interface for every switch statement you
currently have.

Does that approach make sense now?

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