General guidelines on how to design classes with best known industry practices.

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81
votes
9answers
8k 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 ...
52
votes
12answers
3k views

Is it bad practice to pass instances through several layers?

In my program design, I often come to the point where I have to pass object instances through several classes. For example, if I have a controller that loads an audio file, and then passes it to a ...
51
votes
6answers
6k views

Should a getter throw an exception if its object has invalid state?

I often run into this problem, especially in Java, even if I think it's a general OOP issue. That is: raising an exception reveals a design problem. Suppose that I have a class that has a String name ...
36
votes
9answers
4k views

Is creating subclasses for specific instances a bad practice?

Consider the following design public class Person { public virtual string Name { get; } public Person (string name) { this.Name = name; } } public class Karl : Person { ...
25
votes
10answers
6k views

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 ...
19
votes
2answers
1k views

Is it a good idea to provide different function signatures that do the same thing?

Here is a C++ class that gets constructed with three values. class Foo{ //Constructor Foo(std::string, int, char); private: std::string foo; char bar; int baz; }; All of ...
16
votes
5answers
1k views

How can you decompose a constructor?

Lets say I have a Enemy class, and the constructor would look something like: public Enemy(String name, float width, float height, Vector2 position, float speed, int maxHp, int ...
15
votes
9answers
7k views

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 ...
15
votes
7answers
1k views

What's the idea behind naming classes with “Info” suffix, for example: “SomeClass” and “SomeClassInfo”?

I'm working in a project which deals with physical devices, and I've been confused as how to properly name some classes in this project. Considering the actual devices (sensors and receivers) are one ...
14
votes
9answers
1k views

Isn't class scope purely for organization? [duplicate]

Isn't scope just a way to organize classes, preventing outside code from accessing certain things you don't want accessed? More specifically, is there any functional gain to having public, protected, ...
13
votes
6answers
2k views

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
votes
4answers
2k views

Is It “Wrong”/Bad Design To Put A Thread/Background Worker In A Class?

I have a class that will read from Excel (C# and .Net 4) and in that class I have a background worker that will load the data from Excel while the UI can remain responsive. My question is as follows: ...
12
votes
2answers
592 views

Taming the 'utility functions' classes

In our Java codebase I keep seeing the following pattern: /** This is a stateless utility class that groups useful foo-related operations, often with side effects. */ public class FooUtil { ...
11
votes
4answers
13k views

Is it a good practice to create a ClassCollection of another Class?

Lets says I have a Carclass: public class Car { public string Engine { get; set; } public string Seat { get; set; } public string Tires { get; set; } } Lets say we're making a system ...
11
votes
4answers
7k views

C++ - Constructor or Initialize Method to Startup [duplicate]

Possible Duplicate: Avoid having an initialization method I want to determine when to do non-trivial initialization of a class. I see two times to do initialization: constructor and other ...
11
votes
4answers
1k views

Object Oriented Programming: getters/setters or logical names

I'm currently thinking about an interface to a class I'm writing. This class contains styles for a character, for example whether the character is bold, italic, underlined, etc. I've been debating ...
11
votes
3answers
3k views

Abstract Base Class with Interfaces as Behaviors?

I need to design a class hierarchy for my C# project. Basically, class' functionalities are similar to WinForms classes so let's take WinForms toolkit as an example. (However, I can't use WinForms or ...
10
votes
6answers
2k views

At what point do immutable classes become a burden?

When designing classes to hold your data model I've read it can be useful to create immutable objects but at what point does the burden of constructor parameter lists and deep copies become too much ...
10
votes
3answers
1k views

Base classes as factories?

I was writing some code over the weekend and I found myself wanting to write a factory as a static method in a base class. My question is simply to know if this is a c# idomatic approach? My sense ...
10
votes
4answers
3k views

Why define a Java object using interface (e.g. Map) rather than implementation (HashMap)

In most Java code, I see people declare Java objects like this: Map<String, String> hashMap = new HashMap<>(); List<String> list = new ArrayList<>(); instead of: ...
10
votes
2answers
303 views

is it a reasonable practice to extend a class just to reuse a single function?

I am developing a range of post filters for a wordpress site, and I have built the first 4 with a single class. The final two are different enough in scope to only share a single function (the ...
10
votes
2answers
732 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
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 ...
9
votes
6answers
2k views

Prefer class members or passing arguments between internal methods?

Suppose within the private portion of a class there is a value which is utilized by multiple private methods. Do people prefer having this defined as a member variable for the class or passing it as ...
9
votes
5answers
3k 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
7answers
748 views

Is it appropriate for a class to only be a collection of information with no logic?

Say I have a class Person that has instance variables age, weight, and height, and another class Fruit that has instance variables sugarContent and texture. The Person class has no methods save ...
8
votes
4answers
540 views

What would be the best way to store movements on a game to allow a rollback?

I'm developing a board game that has a game class that controls the game flow, and players attached to the game class. The board is just a visual class, but the control of the movements is all by the ...
8
votes
4answers
4k views

Use Dependency Injection For Data Objects?

I'm just learning about dependency injection, and am stuck on something. Dependency Injection recommends sending dependent classes through the constructor, but I'm wondering if this is necessary for ...
7
votes
3answers
3k views

Data classes: getters and setters or different method design

I've been trying to design an interface for a data class I'm writing. This class stores styles for characters, for example whether the character is bold, italic or underlined. But also the font-size ...
7
votes
5answers
3k views

Can You Have “Empty” Abstract/Classes?

Of course you can, I'm just wondering if it's rational to design in such a way. I'm making a breakout clone and was doing some class design. I wanted to use inheritance, even though I don't have to, ...
7
votes
2answers
3k views

Why prefer non-static inner classes over static ones?

This question is about whether to make an inner class in Java static or not. I searched around here and on StackOverflow, but couldn't really find any questions regarding the design implications of ...
6
votes
4answers
727 views

Method flags as arguments or as member variables?

I think the title "Method flags as arguments or as member variables?" may be suboptimal, but as I'm missing any better terminology atm., here goes: I'm currently trying to get my head around the ...
6
votes
10answers
525 views

Teaching Classes and Objects [closed]

I'm trying to teach how an object is just an instance of a class to a buddy of mine. However, he doesn't seem to understand it so well. I've heard a ton of the examples (blueprint to a house, etc.) ...
6
votes
6answers
399 views

Fields vs method arguments [closed]

I just started writing some new class and it occurred to me that I was adding a lot of method arguments that are not strictly needed. This is following a habit to avoid having state in classes that is ...
6
votes
6answers
1k views

Organizing Class Members in Regards to Access Modifier

If we look at typical implementation of a Class, we usually see the private members defined at the beginning and public( mostly functions and Accessors) defined towards the bottom. Now, is this a ...
6
votes
3answers
171 views

Grouping conceptual algorithms into one class or associate with their object models

If I have a number of classes, lets say a variety of buildings of some sort. Each of these buildings have various properties and do some stuff etc Now there is a set of operations I need to do on ...
5
votes
3answers
4k views

Can a class be inside another class?

Here's an excerpt from "The C++ Programming Language" template<classT> class List { // optimal public: class Link { /* ... */ }; List (); // initially empty void put(T *); // put before current ...
5
votes
7answers
2k views

Where should I put my utility methods?

I am very new to Visual Studio and C# and am wondering how best to create a repository of sorts for utility methods. For instance, we need a method that returns the current fiscal year and other ...
5
votes
2answers
470 views

Should I expose a “computed” value as a property or a method?

I have a C# class that represents a content type in a web content management system. We have a field that allows a web content editor to enter an HTML template for how the object is displayed. It ...
5
votes
3answers
244 views

OOP Practice: how to best handle dependent dependencies

I have a problem with the design shown in the picture. My Section class has some TextBlocks (or simply Blocks). The section should be drawn on a page (a Bitmap as device context). It sets the blocks ...
5
votes
1answer
380 views

Decoupling when constructors have non-contractual parameters

By non-contractual parameters, I mean parameters that are not interfaces or service dependencies, something like class Person(string name). I am writing a webpage scraping application, and so far ...
5
votes
4answers
275 views

Best way to handle class relationship

Take a User class and the idea that a User is to be profiled. I see four ways to handle this: Write the code for the profile into the User class. I am dismissing this right away. Create a Profile ...
5
votes
3answers
250 views

How to name an subclass that add a minor, detailed thing?

What is the most concise (yet descriptive) way of naming a subclass that only add a specific minor thing to the parent? I encountered this case a lot in WPF, where sometime I have to add a small ...
5
votes
1answer
169 views

How to design an algorithm-heavy and object-light application

Other than vertices, edges, faces and meshes, my geometry processing project/application has only about half a dozen other entities such as curves on surfaces. However the majority of my code is ...
5
votes
2answers
576 views

Should exceptions of a subclass extend the superclass exceptions or my own namespace?

Our library extends another (third-party) library. When we create a child class in our library, and want to throw exceptions, should those exceptions extend the exceptions from the parent class or ...
5
votes
1answer
360 views

Mutable with logic inside or immutable with logic outside?

I know immutable objects are preferred to mutable objects for reasoning and maintenance. But in occasions making a class immutable have some costs, let me explain it with a simple example: class ...
5
votes
2answers
297 views

Should I use events or abstract methods?

Lets say I create an abstract class that manages some network functionality for me. I want to be able to be notified when something changes. For example: OnConnect or OnDisconnect. Should I create ...
4
votes
3answers
474 views

Why is it so difficult to know where to use interfaces,generics in program design?

I am attempting to learn c# from the head first series, in addition i also consult other books such as Pro C# by Andrew Tolson. Now the thing is that i perfectly understand the interface,generics ...
4
votes
2answers
301 views

dealing with a very large state machine in a class

I am currently implementing a class for a network protocol. The protocol uses a quite complex and extensive finite state machine. A pair of an event plus a state is mapped to a function, which does ...
4
votes
2answers
1k views

How to deal with pointers from child to parent?

I have a class that represents a file in specific binary format on disk (the parent in the title) and another class that represents an object inside that file (child). When the object changes, it ...