Design patterns Static factory method Hiding direct access to constructor
Example
We can avoid providing direct access to resource intensive constructors, like for databases. 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);
//...
}
}
