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 ...
71
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7answers
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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 ...
63
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17answers
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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 ...
56
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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 ...
52
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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 ...
51
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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 ...
51
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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 ...
39
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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) ...
33
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8answers
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Is OOP becoming easier or harder?

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(); ...
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 ...
25
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7answers
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Are classes with only a single 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 ...
24
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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 ...
24
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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 ...
22
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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 ...
22
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10answers
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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 ...
21
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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 ...
20
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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 ...
19
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4answers
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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 ...
19
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6answers
906 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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8answers
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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 ...
17
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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 ...
17
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3answers
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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 ...
16
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10answers
876 views

Object Oriented Design

Suppose you have the following: +--------+ +------+ | Animal | | Food | +-+------+ +----+-+ ^ ^ | | | | ...
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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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 ...
15
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3answers
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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; ...
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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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 ...
13
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5answers
833 views

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 ...
13
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4answers
657 views

Switch vs Polymorphism when dealing with model and view

I can't figure out a better solution to my problem. I have a view controller that presents a list of elements. Those elements are models that can be an instance of B, C, D, etc and inherit from A. So ...
11
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3answers
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How to create better OO code in a relational database driven application where the database is poorly designed

I am writing a Java web application that consists mainly of a bunch of similar pages in which every page has several tables and a filter that applies to those tables. The data on these tables comes ...
11
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7answers
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OO best practices for C programs

"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++ ...
11
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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 ...
11
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7answers
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From a design perspective, what are the best practices for logging? [closed]

I want to add logging to an application I'm currently working on. I've added logging before, that's not an issue here. But from a design perspective in an object-oriented language, what are the best ...
10
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7answers
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What are the features required for Object Orientation?

I am just wondering, what exactly are the features a language or a library must provide in order for it to be defined as 'Object Oriented'. Is Object Orientation something that can, more or less, be ...
10
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9answers
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SOLID vs. static methods

Here's a problem I frequently run into: Let there be a web shop project that has a Product class. I want to add a feature which allows users to post reviews to a product. So I have a Review class ...
10
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2answers
701 views

Design: Object method vs separate class's method which takes Object as parameter?

For example, is it better to do: Pdf pdf = new Pdf(); pdf.Print(); or: Pdf pdf = new Pdf(); PdfPrinter printer = new PdfPrinter(); printer.Print(pdf); Another example: Country m = new ...
9
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7answers
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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 ...
9
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3answers
629 views

Do I suffer from encapsulation overuse?

I have noticed something in my code in various projects that seems like code smell to me and something bad to do, but I can't deal with it. While trying to write "clean code" I tend to over-use ...
9
votes
4answers
529 views

Good implementation strategies for encapsulating shared data in a software pipeline

I'm working on re-factoring certain aspects of an existing web service. The way the service APIs are implemented is by having a kind of "processing pipeline", where there are tasks that are performed ...
8
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4answers
900 views

Is the List interface a leaky abstraction?

If I have a variable containing a List it could contain objects of a lot of different types e.g. ArrayList or LinkedList. The difference between a LinkedList and an ArrayList is pretty big. The big O ...
8
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6answers
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What are the differences between abstract classes, interfaces, and when to use them

Recently I have started to wrap my head around OOP, and I am now to the point where the more I read about the differences between abstract classes and interfaces the more confused I become. So far, ...
8
votes
10answers
723 views

What should be first - functionality or design? [duplicate]

I've started reading a book from Head First series about OOP and Design. In a first chapter it is stated I have to worry about design of my application just after basic functionality is ready. Basic ...
8
votes
2answers
547 views

How to create the architecture/design of an application in Agile?

If I am about to develop an Enterprise application, but as far as I understand from agile process, I break features into small chunks and develop them iteratively. I used to create the database and ...
8
votes
4answers
783 views

How do we keep dependent data structures up to date?

Suppose you have a parse tree, an abstract syntax tree, and a control flow graph, each one logically derived from the one before. In principle it is easy to construct each graph given the parse tree, ...
8
votes
4answers
645 views

Design in “mixed” languages: object oriented design or functional programming?

In the past few years, the languages I like to use are becoming more and more "functional". I now use languages that are a sort of "hybrid": C#, F#, Scala. I like to design my application using ...
8
votes
2answers
287 views

When following SRP, how should I deal with validating and saving entities?

I've been reading Clean Code and various online articles about SOLID lately, and the more I read about it, the more I feel like I don't know anything. Let's say I'm building a web application using ...
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7answers
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Should I create interfaces for data transfer objects?

Is it a good idea or a bad idea to create an interface for data transfer objects? Presuming that the object is usually mutable. Though my example is in Java, it should be applicable to any other ...
7
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4answers
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Can I consider interface methods as abstract methods?

I was thinking about that, and I had some doubts. When I declare an interface, for example: public interface MyInterface { public void method1(); public void method2(); } Could these ...
7
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6answers
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Design: Calling back to the parent class

When modelling an object with children it's common to include the children via composition, as a member of the parent class. Sometimes however the children need to tell the parent something, they need ...