import java.util.Hashtable;

public class PersistenceFacade {

    public Object get(OID oid, Class c)
    {
        IMapper mapper = (IMapper) mappers.get(c);
        return mapper.get(oid);
    }

    public void put(OID oid, Object o)
    { /* ... */ }

    private Hashtable mappers;

    {
        mappers = new Hashtable();
        mappers.put(City.class, new CityRDBMapper());
    }

    // this is a singleton

    protected PersistenceFacade() { }

    private static PersistenceFacade instance;

    public static PersistenceFacade getInstance()
    {
        if (instance == null) {
            instance = new PersistenceFacade();
        }
        return instance;
    }

}