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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9
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8answers
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Designs and practices to guard against erroneous null entries from database

One part of my program fetches data from many tables and columns in my database for processing. Some of the columns might be null, but in the current processing context that is an error. This should "...
16
votes
8answers
3k views

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 ...
6
votes
3answers
2k views

How to solve circular dependency?

I have three classes that are circular dependant to each other: TestExecuter execute requests of TestScenario and save a report file using ReportGenerator class. So: TestExecuter depends on ...
24
votes
6answers
3k views

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 ...
2
votes
1answer
108 views

Pass request as argument to service client vs. pass service client as argument to request [closed]

I need a design recommendation: I have a class that send a http request via another class WebServiceHandler() I am hesitating between the following two implementations, which one to choose?which one ...
3
votes
1answer
110 views

Does my design break modularity and loose coupling?

I want to know if my implementation is modular and loosely coupled such that pieces can be replaced easily. Any concrete class that extends the abstract class HexGridLayout will be expected to ...
2
votes
2answers
113 views

Should the Vector type inherit from the Array type in an environment where both are first-class objects

I have created a programming language that is based on java for a personal project. The language already has generic classes and functions and the generics are completely compatible with primitive ...
0
votes
0answers
23 views

Which design pattern for interaction with miscoded project [duplicate]

I am actually working on JavaEE application (Spring, Hibernate). I have an old project which is not well coded. I have to not modify any line of code on it. And I have to add classes that uses this ...
5
votes
4answers
365 views

Dependency Inversion Principle and Hollywood analogy

Often DIP is known as the Hollywood principle: "Don't call us, we'll call you.". But doesn't always higher level module calls lower level module, whether there is dependency inversion or not? Then ...
1
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1answer
166 views

When should interface be owned by client?

In Agile Software Development: Principles, Patterns, and Practices, Uncle Bob talks about client owning the service interface. My questions are : Should client always own the interface or only ...
0
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0answers
102 views

Generic Type Parameters where one is itself Generic with a Type Parameter of the Other

I have a couple of classes with the following pattern that I am uncomfortable with. Is this the only way to do this, or are their other design patterns that would be more reliable. public class ...
2
votes
1answer
201 views

How to implement a facade correctly

I have read multiple websites on this topic but none of them gave me a 'good' solution for the problem I am having. The problem is described in the following (related) questions: How do I couple the ...
-2
votes
1answer
155 views

Is there a pattern to map a range of numbers to a string?

I need a function that will take the name of a town and return a specific range of numbers that is assigned to that town. I won't be using a database. The simplest way to do this is //Pseudocode ...
1
vote
3answers
147 views

How To Extend Parent Methods in Children Classes?

There is a parent class with a method which many children use but many children extend the method, what is the best way to extend it without violating DRY? Here are my 2 current solutions: 1: The ...
5
votes
1answer
105 views

Object-Oriented design to create Images in Python

I'm creating images with centered text. I use Python but I'm faced with many question regarding how to write my class. I know that A class must aim to do one thing and do it well. Well, the ...
0
votes
1answer
113 views

Should I hold an Id and the Item [duplicate]

Let's say I have a Customer which contains an Address class like: public class Customer { public int Id { get; set; } public string FirstName { get; set; } public string LastName { get; ...
6
votes
5answers
1k views

Does this code solve the square/rectangle Liskov Substution Principle example?

I just wanted to check that I understand the LSP correctly and can solve it. I am taking the classic rectangle/square problem and attempting a solution: class Rectangle{ public $width; ...
3
votes
1answer
187 views

Why is abstract Decorator class needed in this example?

Why do we need ShapeDecorator in this design? Why can't we just have RedShapeDecorator implement Shape directly and inherit from Shape?
2
votes
2answers
176 views

Private variables and the old FORTRAN common blocks [closed]

This is a question that perplexes me about object oriented programming. In some OOP languages (e.g. C++) a member function can access private variables of the class without restriction. That means ...
12
votes
5answers
797 views

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 ...
1
vote
3answers
82 views

Java Object Oriented Question - 2

This is yet another follow up question about Object oriented design in general. I am trying to break them down to separate questions per advice I got from @Jay earlier. I get a new question, almost ...
2
votes
2answers
142 views

How is polymorphism better than two function calls in this example [ATM design]?

So I've finally started reading Designing Object-Oriented Software and my needle is stuck at a small but important point. I understand that the example I'm about to present might appear a bit out of ...
1
vote
3answers
219 views

Why do we need a context class in strategy pattern?

For the strategy pattern, why do we need a context class to call the appropriate algorithm? Why cant we just do Strategy s=new OperationAdd()? This way we still use polymorphism.
2
votes
2answers
197 views

Passing fields (instance variables) by arguments (parameters) inside an object - does it make sense? [duplicate]

I believe this is language agnostic question - if it's not then please correct me. Let's say I have a class (code snippet is a kind of 'pseudo code') class Car: private steering_wheel private ...
5
votes
5answers
636 views

Advantages of Strategy Pattern

Why is it beneficial to use the strategy pattern if you can just write your code in if/then cases? For example: I have a taxPayer class, and one of its methods calculates the taxes using different ...
12
votes
4answers
1k 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 ...
0
votes
1answer
90 views

Object oriented programming - subobject vs globals (use case) [closed]

I am developing a nethack-like game, and I would like an advice how to approach the design part. For now I got class like Location, Npc, Item etc. But I've got a problem how to easily access parts of ...
9
votes
4answers
525 views

Are there any significant disadvantages to depending upon abstractions?

I was reading this wiki on the Stable Abstractions Principle (SAP). The SAP states that the more stable a package the more abstract it should be. This implies that if a package is less stable (more ...
3
votes
2answers
203 views

Design pattern for fetching data in chunks

I am creating Qt application that uses database with huge amount of data to draw some charts. Fetching data from the database is time consuming, so is blocking the application thread or worker thread ...
1
vote
4answers
111 views

How to design class model for specific products, some of which may contain groups of specific product models

Class Design Question I am trying to figure out a good way to design my class system. I have a class Product to compute various product specifications. I have two product model groups, each ...
5
votes
2answers
202 views

Object Oriented Late Binding

In the Alan Kays Definition Of Object Oriented there is this definition that partially I don't understand: OOP to me means only messaging, local retention and protection and hiding of state-...
0
votes
4answers
86 views

Public and Private Constructors with Equivalent Signatures

Here is the problem illustrated using an example of an immutable class. A Book must have at least one of a title and an ISBN. public class Book { private readonly string _title; private ...
1
vote
2answers
229 views

Code quality : what's the worth of the looking at the ifs?

We've all seen discussions on the ideal length of a method. My favourite litmus test for code quality is to look at the "if" statements, to see whether the values being tested belong to the current ...
3
votes
1answer
204 views

Why throw a 'must implement this function' exception rather than making the function abstract?

In the Android support libraries here the destroyItem and instantiateItem functions throw an exception if they aren't overriden: 175 throw new UnsupportedOperationException( 176 ...
4
votes
3answers
290 views

How to avoid the LoadBy pattern?

In our codebase for a sophisticated system controlling many aspects of businesses, we have a certain unwritten law to not fudge around in code with complicated SQL, instead writing it into a function ...
6
votes
2answers
298 views

Automatic namespace resolution in C++

My question is focused on design, and the code included in this question is meant to clarify the problem I'm experiencing. I'm interested in conceptual level answers and not code in order to answer ...
1
vote
1answer
70 views

OO Design: Reading/Writing object with multiple formats

I have a class Song, which has the following public methods: String getSong(); void setSong(String); int getId(); void setId(int); Now I have two different ways I might want to store these songs in ...
0
votes
1answer
235 views

Rich Model vs God Class [duplicate]

I have a legacy code containing some behaviour classes, like services and controllers. My model is pretty anaemic. It's just a repository of getters and setters, and I want to refactor it. There is a ...
0
votes
1answer
69 views

Parsing an object from multiple source files

I receive zip files and they have as content 8 different files, each with it's own metadata inside. I have to combine these files into 1 object containing certain metadata. The big issue here is that ...
1
vote
1answer
129 views

Is this the preferred way to do inheritance in JavaScript?

Hey there I'm not new to programming nor javascript but I'm new to the object oriented world of javascript as it differs from languages I know such as java, c# when it comes to object oriented apsects....
1
vote
2answers
505 views

Class design for writing multiple versions of multiple files

I am writing a web service in Java which reads some information from a DB and generates multiple JSON files which are written to S3. For each type of file, I have a POJO which is serialized to JSON ...
1
vote
3answers
100 views

Inheritance or type field when designing class

I have to model a store with all kinds of articles. The user has to be able to filter these articles by type, price, ... . The store would contain a list of Article objects. I've been stuck on ...
1
vote
2answers
71 views

Direct Dependency Injection and Logger

Lets say I use Dependency Injection and don't use a DI framework. So the injection is direct rather automatic. How I should handle the logger class? All the objects, (thousands) should have a Logger ...
2
votes
1answer
62 views

Dynamic configuration of the software

This post teaches us to separate object graph construction from the application logic into two different classes and the end goal is to have either: classes with logic OR classes with “new” operators. ...
1
vote
2answers
189 views

Design of an online book reader

I want to design an online book reader system as a programming exercise. I wrote down the following requirements: Searching a book by title. Bookmarking a book. Mark a book as favorite. Give rating. ...
1
vote
1answer
156 views

Interface Implementation: A parameter I don't need

Pseudo-Code interface IPagingInfo { int CurrentPageNo { get; } int RowsPerPage { get; } ... } interface ResultsRetriver { ResultRows GetResults(IPagingInfo pagingInfo); } class ...
1
vote
1answer
142 views

Interface Design: Specific vs General parameter (A Minimal design vs anticipated use variation)

Code public interface IVehicle { string VehicleMake { get; } int MonthsSincePurchase { get; } bool IsApprovedUsed { get; } ... } public class WarrantyPopUpHandler { virtual bool ...
0
votes
2answers
234 views

Do we need servant pattern? What about implementing in parent class?

From wikipedia: Servant is used for providing some behavior to a group of classes. Instead of defining that behavior in each class - or when we cannot factor out this behavior in the common ...
29
votes
4answers
4k views

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; ...
33
votes
6answers
4k views

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 ...