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.

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73
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13answers
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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 ...
71
votes
14answers
18k 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 ...
49
votes
9answers
3k views

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

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 ...
44
votes
17answers
4k views

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

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 ...
41
votes
11answers
8k views

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

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 ...
36
votes
9answers
4k 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 ...
33
votes
3answers
1k views

Does Java development typically involve more subclassing than C#/.NET?

I've recently started looking at Android development. This has brought me back into the world of Java software development. The last time I worked with Java, I'll admit, I didn't understand OOP nearly ...
27
votes
1answer
5k views

Multiple Interfaces in Java - Good or bad [closed]

I'm coming out of an interview just now and the interviewer asked me if a Java interface can "extend" more than one interfaces. I was thinking multiple inheritance is disallowed in java so got that ...
26
votes
4answers
12k 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 ...
25
votes
5answers
1k views

Many small classes vs. logical (but) intricate inheritance

I'm wondering what is better in terms of good OOP desing, clean code, flexibility and avoiding code smells in the future. Image situation, where you have a lot of very similar objects you need to ...
24
votes
9answers
3k views

Are abstract classes / methods obsolete?

I used to create a lot of abstract classes / methods. Then I started using interfaces. Now I am not sure if interfaces aren't making abstract classes obsolete. You need a fully abstract class? ...
24
votes
4answers
4k views

How prototypal inheritance is practically different from classical inheritance?

Inheritance, Polymorphism, and Encapsulation are the three most distinct, important features of OOP, and from them, inheritance has a high usage statistics these days. I'm learning JavaScript, and ...
19
votes
7answers
1k views

Should I test inherited methods?

Suppose I have a class Manager derived from a base class Employee, and that Employee has a method getEmail() that is inherited by Manager. Should I test that the behaviour of a manager's getEmail() ...
17
votes
3answers
13k 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 ...
13
votes
3answers
1k 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 ...
13
votes
4answers
2k 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 ...
12
votes
6answers
2k views

Real-world scenarios for protected methods

Today I noticed that I basically never use protected methods in C++ code, because I rarely feel the need to call non-public methods of a parent. I do use protected in Java in the template method ...
11
votes
12answers
2k views

Is “If a method is re-used without changes, put the method in a base class, else create an interface” a good rule-of-thumb?

A colleague of mine came up with a rule-of-thumb for choosing between creating a base class or an interface. He says: Imagine every new method that you are about to implement. For each of them, ...
9
votes
6answers
11k views

Why are constructors not inherited?

I am confused as to what the problems could be if a constructor was inherited from a base class. Cpp Primer Plus says, Constructors are different from other class methods in that they create ...
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 ...
8
votes
5answers
2k 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. ...
8
votes
1answer
289 views

Why is the use of constructors discouraged when creating prototypes?

Quick background: In JavaScript, the constructor function for each object type has a prototype property. The prototype refers to an object that each constructed object uses as the next step up in its ...
8
votes
1answer
823 views

JavaScript objects and Crockford's The Good Parts

I've been thinking quite a bit about how to do OOP in JS, especially when it comes to encapsulation and inheritance, recently. According to Crockford, classical is harmful because of new(), and both ...
7
votes
6answers
2k 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 ...
7
votes
6answers
3k views

When you use inheritance to reuse code, do you find it too tricky that it swallows the benifits of reuse?

I've been coding for about 8 years, however I still find inheritance is too flexible and sometimes it makes you totally confused with the code you have written. One simplest example would be: ...
7
votes
9answers
1k views

What OO Design to use ( is there a Design Pattern )?

I have two objects that represent a 'Bar/Club' ( a place where you drink/socialise). In one scenario I need the bar name, address, distance, slogon In another scenario I need the bar name, address, ...
7
votes
2answers
477 views

How do I avoid writing lots of pass-through functions in a wrapper?

I have a class, which wraps another class of a common base type. Because the base type interface is quite large this involves writing a lot of pass-through functions. I am looking for a way to avoid ...
7
votes
4answers
256 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 ...
6
votes
1answer
240 views

Declaring functions as final… except when it is me who does the deriving

I have a class in which I want to disallow other programmers from overriding one of it's methods, since it requires special knowledge of the inner workings of the class. Since I personally know how ...
6
votes
2answers
1k views

Why Java does not support private/protected inheritance like C++? [closed]

While inheriting a class in C++, user can specify the access specifier like, class Base { public int mem1; protected in mem2; }; class Derived1 : **private** Base { // mem1 will be ...
6
votes
1answer
245 views

“Super” vs “protected method” for running common code

In many langauges, super() lets you call the parent method which you have overridden. I've been using super in my Javascript (with fake object oriented implementation) to run common code for a long ...
6
votes
5answers
443 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
4answers
810 views

Looking for a real-world example illustrating that composition can be superior to inheritance

I watched a bunch of lectures on Clojure and functional programming by Rich Hickey as well as some of the SICP lectures, and I am sold on many concepts of functional programming. I incorporated some ...
5
votes
9answers
1k 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 ...
5
votes
9answers
471 views

Is there a programming language with not a tree but tags idea behind OOP?

I'm thinking about tree structures, and I feel that I don't like them. It's like when you have a shop, then you try to put all products to tree-like catalog, and then you need to place one product to ...
5
votes
3answers
1k views

When calling a method should we use base.methodname and this.methodname?

In C#, with an inherited class set -- when calling a method should we use keywords 'base.methodname and this.methodname'... irrespective of whether it is a overridden method or not? The code is ...
5
votes
3answers
199 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 ...
5
votes
2answers
779 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 ...
5
votes
2answers
458 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 ...
4
votes
9answers
752 views

Does single inheritance limit what we can do with generalisation?

As a rule of thumb, generalisation is used only in specific circumstances. For example, when we can say that X is literally a subclass of Y. So, we can happily say that a Horse is a subclass of ...
4
votes
5answers
1k views

How often is Inheritance used?

I admit that I am a junior developer, and so far I've only built simple web applications in ASP.NET MVC. But I've never had to use the inheritance aspect of Object Oriented Programming in my own ...
4
votes
3answers
611 views

What is the process of determining which method in a class hierarchy should execute known as?

I thought I understood inheritance and polymorphism, but I was given this question, and I can't, for the life of me, figure out what the proper answer is or what they're trying to get at: The ...
4
votes
6answers
237 views

Using all the parameters of a function

Code Complete (2nd ed.) says: "If you pass a parameter to a routine, use it. If you aren't using it, remove the parameters from the routine interface." However, in the past I sometime had to do ...
4
votes
4answers
851 views

Can a method that must be overridden be considered private?

Suppose I have a class C with a method f() which is meant to be used only within C's implementation, but which should be overridden by C's subclasses. Is it reasonable, or "pythonic", to consider it ...
4
votes
2answers
904 views

Naming methods that do the same thing but return different types

Let's assume that I'm extending a graphical file chooser class (JFileChooser). This class has methods which display the file chooser dialog and return a status signature in the form of an int: ...
4
votes
1answer
285 views

Is using protected inheritance to hide (but exploit) implemented interface from the public ok?

Recently, we had a discussion about code using protected inheritance in order to hide the fact (to client code) a class inherits from a specific base class but to exploit this fact in the ...
4
votes
1answer
472 views

Any valid reason to Nest Master Pages in ASP.Net rather than Inherit?

Currently in a debate at work and I cannot fathom why someone would intentionally avoid Inheritance with Master Pages. For reference here is the project setup: BaseProject ...
3
votes
5answers
2k views

Why does Java allow to implement different interfaces, each containing a method with the same signature?

I recently found out that I can have two interfaces, one containing a method with the same signature as a method in the other interface. And I can have an interface or class that implements both of ...
3
votes
4answers
530 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 ...
3
votes
5answers
3k views

Why we use virtual and override keywords in c#

Can anyone explain me what's the point of overriding base class implementations (if its not abstract), because it's not ethical move to modify features of the parent class according to the wishes of ...