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Editorial Team
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Asked: 2026-05-22T20:18:56+00:00

I’m mostly speaking about Java and classical OOP. Say I’m using DAO pattern. So

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I’m mostly speaking about Java and classical OOP. Say I’m using DAO pattern. So I create interfaces like CustomerDao, AccountDao and others. I would place then into org.example.dao package:

org.example.dao.CustomerDao
org.example.dao.AccountDao
...

This all seems good to me so far. Then I create implementations for these interfaces. Here rises my first question: How do I name them? One practice that I have seen is to use *Impl postfix like CustomerDaoImpl. Or perhaps the name should reflect the nature of the implementation, e.g. AccountDatabaseDao or DatabaseBasedAccountDao? Or may be the name should be left intact and then the package would describe the nature of these implementations? If you suggest one or another way, then where should those implementations be placed? A separate package (what naming logics?) or the same package?

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1 Answer

  1. Editorial Team

    There are two camps: functional and technical naming.

    The one like:

    org.example.customer
org.example.account

    The other like:

    org.example.dao
org.example.service

    I personally like to have the interface and the implementations in one spot and make only the interface public and to package by functionality as the packages have a higher cohesion this way.

    With growing size you can still split the packages in for example org.example.customer.dao, org.example.customer.service and org.example.customer.ui. (Technically this is the same as org.example.dao.customer.dao, org.example.service.customer and org.example.ui.customer as Java packages are not nested.)

    For your example I’d start with:

    org.example.customer.CustomerDao
org.example.customer.DatabaseCustomerDao (package private)
org.example.account.AccountDao
org.example.account.DatabaseAccountDao (package private)

    To make the implementation package private you need a factory to create the instances. If you’re using DI. The DI-framework implements the factory for you and you can inject the instances in the users classes that depend only on the interface contract.

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