Should an abstract class always abstract its methods to an interface?

I had learned sometime ago that abstract classes should always abstract their functions to an interface. So instead of having something like this –

Modeling Associations

I am working on the design phase of a paper folding project. I have a few queries in this.
Part of the problem statement says
” A web can contain one or more ribbons in it. It can also contain a group of ribbons folded together inside it.”

Modeling Associations

I am working on the design phase of a paper folding project. I have a few queries in this.
Part of the problem statement says
” A web can contain one or more ribbons in it. It can also contain a group of ribbons folded together inside it.”

Domain model for a notification system

I’m trying to build a modular notification service in a ASP.NET MVC web application. The application generates notifications and the service is responsible for delivering the notifications to the right users. When creating a domain model for the notification service, inheritance naturally comes to mind.

When would you want two references to the same object?

In Java specifically, but likely in other languages as well: when would it be useful to have two references to the same object?

Choosing a class abstraction when multiple viable approaches exist

I’m having trouble trying to design a class structure for some search functionality. It’s quite possible that I’m approaching this incorrectly altogether, but putting that aside I’m curious how other people would approach a situation as follows:

When to declare @throws with a Scala annotation – abstract parent or concrete implementation?

In this StackOverflow question I asked about the behavior of the @throws annotation in Scala. Now that I understand how it works I want to ask about best practices with using it. Here’s a repost of my code from that question:

Is it considered bad practice to make a DAO call in an object’s constructor?

I am trying to figure out the best design for instantiating an object which requires two separate calls to the data layer through a DAO. The object is not usable until these calls have been made (because it requires the data retrieved from the database). I have come up with three possible solutions:

Is it considered bad practice to make a DAO call in an object’s constructor?

I am trying to figure out the best design for instantiating an object which requires two separate calls to the data layer through a DAO. The object is not usable until these calls have been made (because it requires the data retrieved from the database). I have come up with three possible solutions:

How to generalize a classes that has identical function plus some additional function

I have some designing problems with my project. To illustrate my problem, I’ll use the following two classes from my project.