Object-oriented design is the process of planning a system of interacting objects for the purpose of solving a software problem.

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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 ...
80
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8answers
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Is this a violation of the Liskov Substitution Principle?

Say we have a list of Task entities, and a ProjectTask sub type. Tasks can be closed at any time, except ProjectTasks which cannot be closed once they have a status of Started. The UI should ensure ...
80
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16answers
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Is it wrong to use a boolean parameter to determine behavior?

I have seen a practice from time to time that "feels" wrong, but I can't quite articulate what is wrong about it. Or maybe it's just my prejudice. Here goes: A developer defines a method with a ...
74
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16answers
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Is it better to return NULL or empty values from functions/methods where the return value is not present?

I am looking for a recommendation here. I am struggling with whether it is better to return NULL or an empty value from a method when the return value is not present or cannot be determined. Take ...
65
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11answers
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Why is base-for-all-objects discouraged in C++

Stroustrup says "Don’t immediately invent a unique base for all of your classes (an Object class). Typically, you can do better without it for many/most classes." (The C++ Programming Language Fourth ...
60
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6answers
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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 "business ...
59
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10answers
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My proposed design is usually worse than my colleague's - how do I get better? [closed]

I have been programming for couple of years and am generally good when it comes to fixing problems and creating small-to-medium scripts, however, I'm generally not good at designing large scale ...
54
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10answers
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What is meant by, “A user shouldn't decide whether it is an Admin or not. The Privileges or Security system should.”

The example used in the question pass bare minimum data to a function touches on the best way to determine whether the user is an administrator or not. One common answer was: user.isAdmin() This ...
44
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3answers
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Rich Domain Models — how, exactly, does behavior fit in?

In the debate of Rich vs. Anemic domain models, the internet is full of philosophical advice but short on authoritative examples. The objective of this question is to find definitive guidelines and ...
41
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9answers
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Programming for future use of interfaces

I have a colleague sitting next to me who designed an interface like this: public interface IEventGetter { public List<FooType> getFooList(String fooName, Date start, Date end) ...
37
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6answers
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Should I create a class if my function is complex and has a lot of variables?

This question is somewhat language-agnostic, but not completely, since Object Oriented Programming (OOP) is different in, for example, Java, which doesn't have first-class functions, than it is in ...
36
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8answers
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Is OOP becoming easier or harder? [closed]

When the concepts of Object Oriented Programming were introduced to programmers years back it looks interesting and programming was cleaner. OOP was like this Stock stock = new Stock(); ...
35
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5answers
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Passing functions into other functions as parameters, bad practice?

We've been in the process of changing how our AS3 application talks to our back end and we're in the process of implementing a REST system to replace our old one. Sadly the developer who started the ...
33
votes
7answers
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Why is chaining setters unconventional?

Having chaining implemented on beans is very handy: no need for overloading constructors, mega constructors, factories, and gives you increased readability. I can't think of any downsides, unless you ...
33
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6answers
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How do I test a system where the objects are difficult to mock?

I am working with the following system: Network Data Feed -> Third Party Nio Library -> My Objects via adapter pattern We recently had an issue where I updated the version of the library I ...
32
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9answers
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When writing object-oriented code, should I always be following a design pattern?

Is there a conceivable design pattern for any object-oriented program? I ask this because recently I saw an implementation of a Door class with a Lock. It was part of a test and the answer said that ...
30
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3answers
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Where to put business logic in MVC design?

I have created a simple MVC Java application that adds records through data forms to a database. My app collects data, it also validates it and stores it. This is because the data is being sourced ...
29
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3answers
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Is a “start”, “run” or “execute” method a good practice?

I'm currently working on a code base that has many classes that implement a Start method. This seems like two-phase construction to me, which I had always considered a bad practice. I can't tell the ...
29
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7answers
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Are classes with only a single (public) method a problem?

I am currently working on a software project that performs compression and indexing on video surveillance footage. The compression works by splitting background and foreground objects, then saving the ...
29
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4answers
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Does C# 6.0's new null-conditional operator go against the Law of Demeter?

The Law of Demeter states the following: Each unit should have only limited knowledge about other units: only units "closely" related to the current unit. Each unit should only talk to its friends; ...
26
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17answers
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What is the value in hiding the details through abstractions? Isn't there value in transparency?

Background I am not a big fan of abstraction. I will admit that one can benefit from adaptability, portability and re-usability of interfaces etc. There is real benefit there, and I don't wish to ...
26
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6answers
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Can you implement “object-oriented” programming without the class keyword?

Say we want to provide an abstraction of an "account" in a bank. Here's one approach, using a function object in Python: def account(): """Return a dispatch dictionary representing a bank ...
26
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How would Functional Programming proponents answer this statement in Code Complete?

On page 839 of the second edition, Steve McConnell is discussing all the ways that programmers can "conquer complexity" in big programs. His tips culminate with this statement: "Object-oriented ...
25
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6answers
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Is there a design pattern to remove the need to check for flags?

I'm going to save some string payload in the database. I have two global configurations: encryption compression These can be enabled or disabled using the configuration in a way that either only ...
25
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10answers
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Can we live without constructors?

Let's say in some reason all objects are created this way $obj = CLASS::getInstance(). Then we inject dependencies using setters and perform starting initialization using $obj->initInstance(); Are ...
25
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4answers
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Using public final rather than private getters

I see most immutable POJOs written like this: public class MyObject { private final String foo; private final int bar; public MyObject(String foo, int bar) { this.foo = foo; ...
24
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7answers
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Why avoid Java Inheritance “Extends”

Good day! Jame Gosling said “You should avoid implementation inheritance whenever possible.” and instead, use interface inheritance. But why? How can we avoid inheriting the structure of an object ...
22
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12answers
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Object Oriented Design

Suppose you have the following: +--------+ +------+ | Animal | | Food | +-+------+ +----+-+ ^ ^ | | | | ...
22
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7answers
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Does functional programming ignore the benefits gained from the “On the Criteria To Be Used in Decomposing Systems into Modules” (data hiding)?

There's a classic article named On the Criteria To Be Used in Decomposing Systems into Modules that I just read for the first time. It makes perfect sense to me, and is probably one of those articles ...
22
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5answers
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Do unit tests sometimes break encapsulation? [duplicate]

I very often hear the following: "If you want to test private methods, you'd better put that in another class and expose it." While sometimes that's the case and we have a hiding concept inside our ...
22
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9answers
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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 ...
21
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6answers
947 views

Should an object know its own ID?

obj.id seems fairly common and also seems to fall within the range of something an object could know about itself. I find myself asking why should my object know its own id? It doesn't seem to have a ...
18
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1answer
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Why does(/did) Bertrand Meyer think subclassing is the only way to extend a “closed” module?

In Meyer's Object-Oriented Software Construction (1988) he defines the open/closed principle as follows: A module will be said to be open if it is still available for extension. For example, it ...
18
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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 ...
17
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11answers
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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? Example: Dog a = new Dog(); Dob b = a; Is there a situation where ...
17
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8answers
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Interfaces on an abstract class

My coworker and I have different opinions on the relationship between base classes and interfaces. I'm of the belief that a class should not implement an interface unless that class can be used when ...
17
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8answers
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Refactoring a long method which is based on large number of switch cases [duplicate]

We are using Java as a backend development language. One year back, we wrote a method which uses switch cases based on Enums values. Since we are continuously adding enum members and according adding ...
17
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6answers
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Does multiple inheritance violate Single Responsibility Principle?

If you have a class which inherits from two distinct classes, does not this mean that your subclass automatically does (at least) 2 things, one from each superclass? I believe there is no difference ...
16
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6answers
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Does functional programming increase the 'representational gap' between problems and solutions? [closed]

Since machine language (e.g., 0110101000110101) computer languages have generally evolved to higher forms of abstraction, generally making it easier to understand the code when it's applied to a ...
16
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7answers
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OO best practices for C programs [closed]

"If you really want OO sugar - go use C++" -- was the immediate response I got from one of my friends when I asked this. I know two things are dead wrong here. First OO is NOT 'sugar', and second, C++ ...
16
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9answers
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When should you use a private/inner class?

To clarify, what I'm asking about is public class A{ private/*or public*/ B b; } vs. public class A{ private/*or public*/ class B{ .... } } I can definitely think of some ...
16
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5answers
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How to make a datatype for something that represents either itself or two other things

Background Here's the actual problem I'm working on: I want a way to represent cards in the card game Magic: The Gathering. Most cards in the game are normal-looking cards, but some of them are ...
15
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5answers
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How are mock objects commonly misused?

I read an article recently which said that mock objects are often misunderstood and misused. Are there any clear mocking anti-patterns which I can look out for?
15
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5answers
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Is SRP (Single Responsibility Principle) objective?

Consider two UI designers who want to design "user attractive" designs. "User attraction" is a concept that is not objective and only resides in the mind of designers. Thus designer A could for ...
14
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5answers
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Should a class know about its subclasses?

Should a class know about its subclasses? Should a class do something that is specific for a given subclass for instance? My instincts tells me that is a bad design, it seems like an anti-pattern of ...
14
votes
2answers
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Illegal in PHP: Is there an OOP design reason?

The below interface inheritance is illegal in PHP, but I think it would be fairly useful in real life. Is there an actual antipattern or documented problem with the below design, that PHP is ...
14
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6answers
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Loose Coupling in Object Oriented Design

I am trying to learn GRASP and I found this explained (here on page 3) about Low Coupling and I was very surprised when I found this: Consider the method addTrack for an Album class, two possible ...
13
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1answer
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Understanding Visitor Pattern

I have a hierarchy of classes that represents GUI controls. Something like this: Control->ContainerControl->Form I have to implement a series of algoritms that work with objects doing various ...
12
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5answers
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How to avoid violating the SRP in a class to manage caching?

Note: The code sample is written in c#, but that shouldn't matter. I've put c# as a tag because I can't find a more appropiate one. This is about the code structure. I'm reading Clean Code and trying ...
12
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4answers
901 views

How does having too many instance variables lead to duplicate code?

According to Refactoring to Patterns: When a class is trying to do too much, it often shows up as too many instance variables. When a class has too many instance variables, duplicated code ...