What are static factory methods?

Question

What's a "static factory" method?

Answer 1

We avoid presenting a direct path to database connections because they're resource-intensive. So we use a static factory method to get a connection that forms a connection if we're beneath the limit. Unless, it tries to present a "spare" connection, failing with an exemption if there are none.

public class DbConnection{

   private static final int MAX_CONNS = 100;

   private static int totalConnections = 0;

   private static Set<DbConnection> availableConnections = new HashSet<DbConnection>();

   private DbConnection(){

     // ...

     totalConnections++;

   }

   public static DbConnection getDbConnection(){

     if(totalConnections < MAX_CONNS){

       return new DbConnection();

     }else if(availableConnections.size() > 0){

         DbConnection dbc = availableConnections.iterator().next();

         availableConnections.remove(dbc);

         return dbc;

     }else {

         throw new NoDbConnections();

     }

   }

   public static void returnDbConnection(DbConnection dbc){

     availableConnections.add(dbc);

     //...

   }

}