Questions tagged [object-oriented]

A methodology that enables a system to be modeled as a set of objects that can be controlled and manipulated in a modular manner

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81 votes
2 answers
12k views

Are there any OO-principles that are practically applicable for Javascript?

Javascript is a prototype-based object oriented language but can become class-based in a variety of ways, either by: Writing the functions to be used as classes by yourself Use a nifty class system ...
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197 votes
13 answers
138k views

When are Getters and Setters Justified?

Getters and setters are often criticized as being not proper OO. On the other hand, most OO code I've seen has extensive getters and setters. When are getters and setters justified? Do you try to ...
46 votes
8 answers
12k views

What is the real responsibility of a class?

I keep wondering if it is legitimate to use verbs that are based on nouns in OOP. I came across this brilliant article, though I still disagree with the point it makes. To explain the problem a bit ...
153 votes
15 answers
46k 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 ...
24 votes
4 answers
11k views

Make methods that do not depend on instance fields, static?

Recently I started programming in Groovy for a integration testing framework, for a Java project. I use Intellij IDEA with Groovy plug-in and I am surprised to see as a warning for all the methods ...
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40 votes
4 answers
12k views

The principle of least knowledge

I understand the motive behind the principle of least knowledge, but I find some disadvantages if I try to apply it in my design. One of the examples of this principle (actually how not to use it), ...
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17 votes
4 answers
2k views

Staying OO and Testable while working with a database

What are some OOP strategies for working with a database but keeping things unit testable? Say I have a User class and my production environment works against MySQL. I see a couple possible approaches,...
240 votes
15 answers
236k views

Why do we need private variables?

Why do we need private variables in classes? Every book on programming I've read says this is a private variable, this is how you define it but stops there. The wording of these explanations always ...
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53 votes
9 answers
18k views

Explanation on how "Tell, Don't Ask" is considered good OO

This blogpost was posted on Hacker News with several upvotes. Coming from C++, most of these examples seem to go against what I've been taught. Such as example #2: Bad: def check_for_overheating(...
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59 votes
8 answers
15k views

How do I prove or disprove "God objects" are wrong?

Problem Summary: Long story short, I inherited a code base and a development team I am not allowed to replace and the use of God Objects is a big issue. Going forward, I want to have us re-factor ...
75 votes
14 answers
8k views

Clarify the Single Responsibility Principle

The Single Responsibility Principle states that a class should do one and only one thing. Some cases are pretty clear cut. Others, though, are difficult because what looks like "one thing" when ...
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40 votes
6 answers
37k views

Understanding "programming to an interface"

I have come across the term "programming to an interface instead of an implementation" a lot, and I think I kind of understand what it means. But I want to make sure I understand it's benefits and it'...
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134 votes
4 answers
28k views

So what *did* Alan Kay really mean by the term "object-oriented"?

Reportedly, Alan Kay is the inventor of the term "object oriented". And he is often quoted as having said that what we call OO today is not what he meant. For example, I just found this on ...
12 votes
6 answers
4k views

What are the practical ways to implement the SRP?

Simply what are the practical techniques people use to check if a class violates the single responsibility principle? I know that a class should have only one reason to change, but that sentence is ...
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145 votes
14 answers
110k views

What is the ideal length of a method for you? [closed]

In object-oriented programming, there is of course no exact rule on the maximum length of a method , but I still found these two quotes somewhat contradicting each other, so I would like to hear what ...
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74 votes
11 answers
53k views

Can't I just use all static methods?

What's the difference between the two UpdateSubject methods below? I felt using static methods is better if you just want to operate on the entities. In which situations should I go with non-static ...
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63 votes
8 answers
27k views

Is ORM an Anti-Pattern? [closed]

I had a very stimulating and interessting discussion with a colleague about ORM and its pros and cons. In my opinion, an ORM is useful only in the rarest cases. At least in my experience. But I don't ...
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57 votes
9 answers
22k 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 ...
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19 votes
3 answers
10k views

How does strengthening of preconditions and weakening of postconditions violate Liskov substitution principle?

I read that Liskov's substitution principle is violated if : Preconditions are strengthened, or Postconditions are weakened But I don't get fully yet how these two points would violate Liskov ...
  • 5,067
274 votes
14 answers
118k views

Should we avoid object creation in Java?

I was told by a colleague that in Java object creation is the most expensive operation you could perform. So I can only conclude to create as few objects as possible. This seems somewhat to defeat ...
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46 votes
3 answers
34k views

Programming SOLID Principles

Over time I could understand two parts of SOLID – the “S” and “O”. “O” – I learned Open Closed Principle with the help of Inheritance and Strategy Pattern. “S” – I learned Single Responsibility ...
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82 votes
12 answers
52k views

What's the benefit of object-oriented programming over procedural programming?

I'm trying to understand the difference between procedural languages like C and object-oriented languages like C++. I've never used C++, but I've been discussing with my friends on how to ...
  • 2,119
97 votes
5 answers
31k views

Functional Programming vs. OOP [closed]

I've heard a lot of talk about using functional languages such as Haskell as of late. What are some of the big differences, pros and cons of functional programming vs. object-oriented programming?
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58 votes
9 answers
44k views

Should the methods of a class call its own getters and setters?

Where I work I see lots of classes that do things like this: public class ClassThatCallsItsOwnGettersAndSetters { private String field; public String getField() { return field; }...
18 votes
6 answers
4k views

Method chaining vs encapsulation

There is the classic OOP problem of method chaining vs "single-access-point" methods: main.getA().getB().getC().transmogrify(x, y) vs main.getA().transmogrifyMyC(x, y) The first seems to have the ...
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18 votes
3 answers
3k 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 ...
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13 votes
1 answer
4k views

Is wrapping a third party code the only solution to unit test its consumers?

I'm doing unit testing and in one of my classes I need to send a mail from one of the methods, so using constructor injection I inject an instance of Zend_Mail class which is in Zend framework. Now ...
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250 votes
23 answers
211k views

If immutable objects are good, why do people keep creating mutable objects? [closed]

If immutable objects¹ are good, simple and offer benefits in concurrent programming why do programmers keep creating mutable objects²? I have four years of experience in Java programming and as I see ...
159 votes
7 answers
100k views

What really is the "business logic"?

I'm working with web development since 2009, when I started with PHP. When I moved to ASP.NET, I've heard a lot about DDD and OOAD where a lot of focus is given to this "business logic" and &...
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79 votes
4 answers
23k views

Why do many software developers violate the open/closed principle?

Why do many software developers violate the open/closed principle by modifying many things like renaming functions which will break the application after upgrading? This question jumps to my head ...
38 votes
3 answers
72k views

When to use a Singleton and when to use a static class [duplicate]

I've searched about this here and on StackOverflow and found some differences between the two. But I'm still not sure in what cases one would prefer a Singleton, and in what cases one would choose to ...
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39 votes
4 answers
13k views

What is the principle of least astonishment?

In programming what is called Principle of Least Astonishment? How is this concept related to designing good APIs? Is this something applicable to only object oriented programming or does it permeate ...
  • 5,067
53 votes
10 answers
11k views

Should we avoid custom objects as parameters?

Suppose I have a custom object, Student: public class Student{ public int _id; public String name; public int age; public float score; } And a class, Window, that is used to show ...
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45 votes
11 answers
10k views

Are error variables an anti-pattern or good design?

In order to handle several possible errors that shouldn't halt execution, I have an error variable that clients can check and use to throw exceptions. Is this an Anti-Pattern? Is there a better way to ...
8 votes
6 answers
1k views

Significant amount of the time, I can't think of a reason to have an object instead of a static class. Do objects have more benefits than I think? [closed]

I understand the concept of an object, and as a Java programmer I feel the OO paradigm comes rather naturally to me in practice. However recently I found myself thinking: Wait a second, what are ...
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95 votes
15 answers
52k views

What makes C so popular in the age of OOP? [closed]

I code a lot in both C and C++, but did not expect C to be the second most popular language, slightly behind Java. TIOBE Programming Community Index I'm curious as to why, in this age of OOP, C is ...
41 votes
3 answers
61k views

What is message passing in OO?

I've been studying OO programming, primarily in C++, C# and Java. I thought I had a good grasp on it with my understanding of encapsulation, inheritance and polymorphism. One frequently referenced ...
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53 votes
20 answers
22k views

Does Object Oriented Programming Really Model The Real World? [closed]

I've seen it commonly repeated the object-oriented programming is based on modeling the real world but is it? It seems to me that is not true of anything outside of the business layer. My GUI classes/...
29 votes
9 answers
10k views

What can go wrong if the Liskov substitution principle is violated?

I was following this highly voted question on possible violation of Liskov Substitution principle. I know what the Liskov Substitution principle is, but what is still not clear in my mind is what ...
  • 5,067
55 votes
3 answers
65k views

Which is a better practice - helper methods as instance or static?

This question is subjective but I was just curious how most programmers approach this. The sample below is in pseudo-C# but this should apply to Java, C++, and other OOP languages as well. Anyway, ...
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16 votes
6 answers
14k views

Are Get-Set methods a violation of Encapsulation? [duplicate]

Possible Duplicate: When are Getters and Setters Justified In an Object oriented framework, one believes there must be strict encapsulation. Hence, internal variables are not to be exposed to ...
  • 10.5k
15 votes
1 answer
3k 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 of ...
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7 votes
4 answers
5k views

When or why should one use getters/setters for class properties instead of simply making them public properties?

I program primarily in ColdFusion but this is a general OOP question. Is there any benefit to using: getProp() { return prop; } setProp(val) { prop = val; } As opposed to simply obj = ...
21 votes
4 answers
3k views

"Too object-oriented"

I come from a strong OO background, and I have recently started working in an organization which, although the code is written in Java, has a lot less emphasis on good OO design than what I am used to....
5 votes
5 answers
6k views

What are the advantages/disadvantages of using objects as parameters to other object methods?

I'm mostly thinking of PHP here, but if you want to refer to other languages that's fine. An object has a method that requires data contained in another class of object. Should I extract that data ...
0 votes
3 answers
425 views

Tell one, but ask the others?

Consider we have three classes which want to collaborate, then, where is the behaviour? I guess it can only be in one of the three classes or in a fourth one acting than as a procuedural connector-...
283 votes
9 answers
282k views

Aggregation vs Composition

I understand what composition is in OOP, but I am not able to get a clear idea of what Aggregation is. Can someone explain?
149 votes
8 answers
24k views

Are bad programming practices typical within the software industry? [closed]

I just started my first job as a software developer over a month ago. Everything I have learned about OOP, SOLID, DRY, YAGNI, design patterns, SRP, etc. can be thrown out the window. They use C# .NET ...
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112 votes
14 answers
30k views

Should I avoid private methods if I perform TDD?

I'm just now learning TDD. It's my understanding that private methods are untestable and shouldn't be worried about because the public API will provide enough information for verifying an object's ...
  • 1,680
45 votes
10 answers
104k views

Why use an interface when the class can directly implement the functions? [duplicate]

Possible Duplicate: Why are interfaces useful? Like most faculty, my java faculty introduced interface without explaining or even mentioning its practical use. Now I imagine interfaces have a ...
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