Inheritance is a way to reuse code of existing objects, or to establish a subtype from an existing object, or both, depending upon programming language support.

learn more… | top users | synonyms

106
votes
14answers
29k views

Where does this concept of “favor composition over inheritance” come from?

In the last few months, the mantra "favor composition over inheritance" seems to have sprung up out of nowhere and become almost some sort of meme within the programming community. And every time I ...
55
votes
4answers
31k views

Why should I prefer composition over inheritance?

I always read that composition is to be preferred over inheritance. A blog post on unlike minds, for example, advocates using composition over inheritance, but I can't see how polymorphism is achieved....
6
votes
4answers
818 views

Are trivial protected getters blatant overkill?

Something I really have not thought about before (AS3 syntax): private var m_obj:Object; protected function get obj():Object { return m_obj; } private var m_str:String; protected function get ...
46
votes
9answers
7k views

Code Smell: Inheritance Abuse [duplicate]

It's been generally accepted in the OO community that one should "favor composition over inheritance". On the other hand, inheritance does provide both polymorphism and a straightforward, terse way of ...
86
votes
12answers
11k views

Why would Square inheriting from Rectangle be problematic if we override the SetWidth and SetHeight methods?

If a Square is a type of Rectangle, than why can't a Square inherit from a Rectangle? Or why is it a bad design? I have heard people say: If you made Square derive from Rectangle, then a Square ...
33
votes
10answers
4k views

Is it okay to have objects that cast themselves, even if it pollutes the API of their subclasses?

I have a base class, Base. It has two subclasses, Sub1 and Sub2. Each subclass has some additional methods. For example, Sub1 has Sandwich makeASandwich(Ingredients... ingredients), and Sub2 has ...
6
votes
2answers
2k views

How does strengthening of pre conditions and weakening of post conditions violate Liskov Substitution principle?

I read that Liskov substitution principle is violated if : Pre conditions are strengthened . Post conditions are eased out. But I don't get fully yet how these two points would violate Liskov ...
7
votes
9answers
2k views

How can designing for inheritance cause extra cost? [closed]

So I wanted to inherit from a sealed class in csharp and got burned. There is just no way to unseal it unless you have access to the source. Then it got me thinking "why sealed even exists?". 4 ...
16
votes
3answers
2k views

Is there a specific name for the “Square inherits from Rectangle” paradox?

A certain failure of OOP is shown with a class Square inheriting from Rectangle, where logically Square is a specialization of Rectangle and should therefore inherit from it, but everything falls ...
17
votes
4answers
5k views

Inheritance vs mixins in dynamic languages?

When should you prefer inheritance patterns over mixins in dynamic languages? By mixins, I mean actual proper mixing in, as in inserting functions and data members into an object in runtime. When ...
5
votes
2answers
2k views

Alternative to “inheritance versus composition?” [duplicate]

Possible Duplicate: Where does this concept of “favor composition over inheritance” come from? I have colleagues at work who claim that "Inheritance is an anti-pattern" and want to use ...
9
votes
5answers
5k views

Interface and Inheritance: Best of both worlds?

I 'discovered' interfaces and I started to love them. The beauty of an interface is that it is a contract, and any object that fulfills that contract can be used wherever that interface is required. ...
3
votes
4answers
974 views

Explanation of the definition of interface inheritance as described in GoF book

I am reading the first chapter of the Gof book. Section 1.6 discusses about class vs interface inheritance: Class versus Interface Inheritance It's important to understand the difference between ...
100
votes
9answers
16k views

Is there any “real” reason multiple inheritance is hated?

I've always liked the idea of having multiple inheritance supported in a language. Most often though it's intentionally forgone, and the supposed "replacement" is interfaces. Interfaces simply do ...
13
votes
1answer
1k views

How to verify the Liskov substitution principle in an inheritance hierarchy?

Inspired by this answer: Liskov Substitution Principle requires that Preconditions cannot be strengthened in a subtype. Postconditions cannot be weakened in a subtype. Invariants ...
2
votes
4answers
3k views

Why 'List<E>' is an 'interface' but not 'abstract class'?

Amidst defining the hierarchy, firstly, one can think to embed the abstract method(behavior) in abstract class only because the derive concrete class possess that behavior as core behavior with it's ...
7
votes
4answers
358 views

Is inheritance that adds rules bad? [duplicate]

I got into a debate on this question which distilled to if it is a good idea for a specialization of a class to add business rules. Unfortunately this point got trampled in the comments so I'm asking ...
4
votes
1answer
711 views

Composition vs. Inheritance [duplicate]

Here's what is given: public interface Request {} // there are 20 subclasses of Request public class CreateUserRequest implements Request { @NotEmpty public String userName; } // request ...
15
votes
3answers
2k views

Are there any OO languages without inheritance?

During a code review today, a colleague of mine said something interesting: prototype is only useful when you need inheritance - and when's inheritance ever a good idea? I thought about this and ...
3
votes
3answers
196 views

Which one subsumes the other: class-based object-orientation or prototypal inheritance?

In this talk: http://www.youtube.com/watch?v=hQVTIJBZook, Douglas Crockford claims that class-based object-orientation can be represented in terms of prototypal inheritance. The construction he gives ...
33
votes
6answers
9k views

LSP vs OCP / Liskov Substitution VS Open Close

I am trying to understand the SOLID principles of OOP and I've come to the conclusion that LSP and OCP have some similarities (if not to say more). the open/closed principle states "software ...
52
votes
17answers
6k views

Is OO-programming really as important as hiring companies place it? [closed]

I am just finishing my masters degree (in computing) and applying for jobs. I've noticed many companies specifically ask for an understanding of object orientation. Popular interview questions are ...
18
votes
3answers
27k views

Best design for Windows forms that will share common functionality

In the past, I have used inheritance to allow the extension of Windows forms in my application. If all of my forms would have common controls, artwork, and functionality, I would create a base form ...
36
votes
1answer
4k views

How are mixins or traits better than plain multiple inheritance?

C++ has plain multiple inheritance, many language designs forbid it as dangerous. But some languages like Ruby and PHP use strange syntax to do the same thing and call it mixins or traits. I heard ...
52
votes
11answers
22k views

Why is it good to split a program into multiple classes? [closed]

I'm still a student in high school (entering 10th grade), and I have yet to take an actual computer course in school. Everything I've done so far is through books. Those books have taught me concepts ...
9
votes
5answers
1k views

How do we know to favour composition over generalisation is always the right choice?

Whether an object physically exists or not, we can choose to model it in different ways. We could arbitarily use generalisation or composition in many cases. However, the GoF principle of "favour ...
3
votes
2answers
4k views

Why is inheritance generally viewed as a bad thing by OOP proponents [duplicate]

I keep hearing the phrase "Favour Composition over Inheritance" from GoF which is being annoyingly mentioned repeatedly by my friend who thinks it is a valid blanket statement but is it not more ...
9
votes
6answers
4k views

Why is subclassing too much bad (and hence why should we use prototypes to do away with it)?

I was reading up on design patterns, and I read that the prototype design pattern does away with excessive subclassing. Why is subclassing bad? What advantage would using a prototype bring about over ...
3
votes
7answers
2k views

Inheritance using non-abstract base class

This post is based on the question http://stackoverflow.com/questions/49002/prefer-composition-over-inheritance/11758048#comment15634305_11758048. Some people said - check whether there is “is-a” ...
7
votes
4answers
332 views

Can I make my constructors less repetitive?

I'm extending a class with 10 different constructors. The new subclass, SpecialImage, is used like this: SpecialImage specialImage = new SpecialImage(..); // Leverage the Rotate() method of ...
3
votes
1answer
518 views

What is the best way to use inheritance with ORMs?

If I have a People table and those people can be at different addresses, and each address can have more than one person, thats a many-to-many relationship. So, using ORMs like Entity Framework and ...
3
votes
2answers
109 views

Database Design for Inheritance

In my project I have an object Player (attr example: pl_id, pl_data1) that is one of these types: Its GoalKeeper (attr example: gk_data1) OR Defender (attr example: df_data1) OR Forward (attr ...
8
votes
2answers
662 views

Who decided on the terminology downcasting and upcasting?

As far as I know, the terminology comes from how the inheritance hierarchy is traditionally displayed, with the extending types at the bottom, and the parent types at the top. This is a bit pointless,...
7
votes
5answers
654 views

Java without implementation inheritance

In a recent video on Java, Joshua Bloch states at 4 minutes 20 seconds into the video: And then there's inheritance, and that was a marketing necessity. You know, we can argue whether you really ...
6
votes
3answers
328 views

How to refactor my design, if it seems to require multiple inheritance?

Recently I made a question about Java classes implementing methods from two sources (kinda like multiple inheritance). However, it was pointed out that this sort of need may be a sign of a design flaw....
3
votes
2answers
708 views

One boilerplate class or many similar classes?

Lets say I'm trying to model a variety of objects that are virtually identical, the only difference being their class variables. Am I better off creating one boilerplate class and just calling the ...
3
votes
5answers
202 views

What is the correct OOP relation between complex and real numbers?

On one hand class complex { double real; double imaginary; } it is composition on the other hand class complex : double { double imaginary; } it is inheritance Which one is ...
2
votes
1answer
78 views

Repeating Interface inheritance declarations

Take the following example: public interface ISerialRVD { RouteValueDictionary ToRVD(); } public interface IViewModel : ISerialRVD // Here? { Int32 Page { get; set; } String Action { get;...
1
vote
1answer
83 views

“Is a” relationship or, in other words Inheritance

Say I define an interface IAnimal which has a pure virtual (abstract) method called eat like this: class IAnimal { virtual void eat(Food*) = 0; }; In the future I inherit form IAnimal and create ...
1
vote
1answer
288 views

Implementation of instance testing in Java, C++, C#

For curiosity purposes as well as understanding what they entail in a program, I'm curious as to how instance testing (instanceof/is/using dynamic_cast in c++) works. I've tried to google it (...
1
vote
2answers
133 views

Expressing interface inheritance in natural language [duplicate]

In object-oriented programming, when you extend a class you establish an is-a relationship between a new subtype and its parent(s), i.e. B is an A (aka code inheritance). When you compose a class with ...
1
vote
1answer
3k views

Code reuse via inheritance [duplicate]

I have a set of classes that are all dealing with some related tasks. These tasks do have different inputs and outputs. This causes it to become impossible to have the tasks done via shared code ...
0
votes
1answer
149 views

When is it suitable to use inheritance [duplicate]

I recently had a small "argument" about inheritance with a friend. I think people overuse it a lot. Intuition tells me that that the only good reason for class inheritance is polymorphism - when there ...
0
votes
2answers
300 views

Inheritance versus Composition in a business application

I have a training management and tracking system, with a high level structure as follows: We have a Role1, e.g. Manager, Shift-boss, miner, etc. and a Candidate, training for that Role. The role has ...
0
votes
1answer
96 views

Matching the superclass's constructor's parameter list, is treating a null default value as a non-null value within a constructor a violation of LSP? [duplicate]

I kind of ran into this when messing around with FlashPunk, and I'm going to use it as an example. Essentially the main sprite class is pretty much class Entity. Entity's constructor has four ...