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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3
votes
2answers
369 views

Implementing “buy one get one for free” coupon logic for shopping cart

Trying to solve bogo coupon logic with proper design pattern, but having trouble identifying one. Use case: "Buy iPad get SmartCase for free" Suppose we have the following objects: Product: - ...
2
votes
2answers
505 views

is it bad practice that controller call repository instead of service?

is it bad practice that controller call repository instead of service? to explain more: I figure out that in good design controllers call service and service use repository. but sometimes in ...
1
vote
2answers
35 views

Exception Handling for class attributes in setters and constructors [closed]

I would like to discuss a question about best practices regarding exception handling (e.g. in Java). Normally, when setting the attributes of a class, I check the arguments in the setters for ...
57
votes
11answers
6k views

Does this class design violate the single responsibility principle?

Today I had an argument with someone. I was explaining the benefits of having a rich domain model as opposed to an anemic domain model. And I demoed my point with a simple class looking like that: ...
26
votes
10answers
3k views

Given a herd of horses, how do I find the average horn length of all unicorns?

The question above is an abstract example of a common problem I encounter in legacy code, or more accurately, problems resulting from previous attempts at solving this problem. I can think of at ...
0
votes
2answers
110 views

Which design pattern to choose when supporting multiple analytic tools?

I have spent quite some time learning all possible design patterns but I cannot find the ideal one for the following case. I am developing an iOS app where we are using multiple analytics tools like ...
-2
votes
1answer
51 views

SRP. Save to repository when edit. Internally or externally? [closed]

For example: class Data { private String field1; private String field2; public void someEditMethod() {} } class DataRepository { public void save(Data data) { // save to DB ...
1
vote
0answers
63 views

Why is conditionally using an empty panel in Apache Wicket a bad practice?

When Apache released its list of best practices, they recommended avoiding the addition of an empty panel conditionally and gave the following example of what NOT to do: if(MySession.get()....
3
votes
1answer
168 views

What is the origin of “Program to an interface, not an implementation”? [closed]

What is the origin of "Program to an interface, not an implementation" -- does it originate from Design Patterns, 1994, by GoF, or from a computer scientist or from some concepts in computer science ...
3
votes
6answers
177 views

If Class is to define attributes and methods, and Interface is to define (a set of) methods, then how to think of interface needing new attributes?

I thought a class is supposed to define, or give a blueprint, of attributes and methods for an object. And then, an interface is to provide a set of methods, as a contract for its clients. (and so a ...
3
votes
2answers
91 views

What is a proper way to implement object cloning with deep copy, using generally accepted OOP principles?

Short version of the question: What is a proper way to implement object cloning with deep copy, using generally accepted OOP principles? I ran into this while looking into the Prototype Design ...
5
votes
4answers
860 views

Does making a method static save memory on a class you'll have many instances of?

In response to Aaronaught's response to the question at: Can't I just use all static methods? Isn't less memory used for a static method? I am under the impression that each object instance carries ...
2
votes
2answers
112 views

Managing widgets in a simple GUI framework

So, I'm still working on my small GUI "library". (C++ with boost) The goal is to provide a simple solution for small SPI displays, using a Raspberry or some embedded board. Thus, I ended up having a ...
6
votes
2answers
226 views

Is Python's inheritance an “is-a” style of inheritance or a compositional style?

Given that Python allows for multiple inheritance, what does idiomatic inheritance in Python look like? In languages with single inheritance, like Java, inheritance would be used when you could say ...
4
votes
1answer
167 views

Using Python's Method Resolution Order for Dependency Injection - is this bad?

I watched Raymond Hettinger's Pycon talk "Super Considered Super" and learned a little bit about Python's MRO (Method Resolution Order) which linearises a classes "parent" classes in a deterministic ...
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 ...
14
votes
3answers
486 views

How wrong is it to talk about C++ “methods” (versus “member functions”)?

I understand that according to the C++ spec there is no such thing as a "method", and some (many? most?) C++ programmers consider "method" to be a Java-ism. On the other hand, even on a C++ forum ...
3
votes
4answers
244 views

Is it the same to say “instantiate a class” and “instantiate an object”? “Instantiate a class” does not mean creating a new class? [closed]

I have seen the phrases "instantiate an object", "instantiate a Square object", or "a Cat object is instantiated." (p.17, p.22, and p.26 of The Object-Oriented Thought Process, 4th Edition, Addison-...
2
votes
1answer
105 views

Persistence Strategies - Filling a cache strategy

Let's say I have an interface IDataAccessObject<TSource> with CRUD methods to access a data source. I have an implementation StrategyDataAccessObject<TSource>, which uses an strategy ...
20
votes
4answers
2k views

Do special-cases with fallbacks violate the Liskov Substitution Principle?

Let's say I have an interface FooInterface that has the following signature: interface FooInterface { public function doSomething(SomethingInterface something); } And a concrete class ...
9
votes
1answer
226 views

Python's join seems to focus not on the items to join, but on the symbol, as compared to Ruby or Smalltalk, for a design reason?

I thought one of the cornerstone of OOP is that, we have objects, which are the items we are interested in dealing with, and then we send messages to them. So it may seem natural that, I have a ...
3
votes
4answers
315 views

Can objects be implemented in terms of higher order functions?

Martin Odersky finished one online course on Scala with an unanswered question: Can we implement one concept in terms of other ? Objects in terms of higher order functions? Higher order functions ...
8
votes
7answers
424 views

Design pattern for “operation on object allowed, only if object is in certain state”

For example: Only job applications that are not yet in review or approved, can be updated. In other words, a person can update his job appliance form until HR starts reviewing it, or it's already ...
2
votes
2answers
130 views

Domain driven design - Entity is updateable in certain circumstances

Here is my business rule: Anyone (anonymous users) can make an Application (as in to apply for something). Applications can be updated until they are reviewed and approved by an officer. Approved ...
16
votes
2answers
1k views

Is it a good idea to define one big private function in a class to maintain valid state, that is, to update the object's data members?

Although in the code below a simple single item purchase in an e-commerce site is used, my general question is about updating all data members to keep an object's data in valid state at all times. I ...
3
votes
1answer
231 views

Command handler executing commands with different dependencies

Well basically, I have an Engine class that recieves a command as string from the input and passes it to a CommandHandler class which executes the apropriate command. The CommandHandler passes the ...
9
votes
4answers
345 views

Best strategy for reporting progress to the UI - how should the callback happen?

Sometimes the user starts an extended technical operation that takes a while to execute. In these cases, it's usually nice to display some kind of progress bar, along with information about which task ...
4
votes
1answer
184 views

Refactoring of a client API for avoid duplicated code and unclear passage of parameters

I need to develop an API, the functions of the API are requests that call the service exposed by a server. Initially the API worked like this: class Server: def firstRequest(self, arg1, arg2): ...
4
votes
3answers
434 views

Avoiding constructors with many arguments

So I have a factory which creates objects of different classes. The possible classes are all derived from an abstract ancestor. The factory has a configuration file (JSON syntax) and decides which ...
5
votes
2answers
210 views

Factories, vectors and smart pointers - Design Question

So, my Business Code needs some Objects. It does not know how much objects it needs and it does not know the exact types (because polymorphism is involved). For me, that sounds for a good reason to go ...
3
votes
1answer
112 views

Single Responsibility Principle : Proxy Pattern for refactoring

However, in cases where the tests did not force the separation, and the smells of Rigidity and Fragility become strong, the design should be refactored using the Facade or Proxy patterns to separate ...
0
votes
2answers
158 views

Designing classes that depend on each other

How would one go about designing classes for a system in which two components depend on each other? For a more concrete example, consider this scenario, you're designing a piece of software to manage ...
2
votes
0answers
42 views

Handling of messages with several indicators

I am currently working on an application, which will show several messages (alarms - warnings - hints) on a cable-connected display. As these messages depend on several indicators I have to decide ...
9
votes
2answers
512 views

Why is it inappropriate to use UML diagrams to plan how your code will be organized?

So, yes, diagrams can be inappropriate at times. When are they inappropriate? When you create them without code to validate them, and then intend to follow them. There is nothing wrong with drawing ...
10
votes
4answers
368 views

Parameter management in OOP application

I'm writing a medium size OOP application in C++ as a way to practice OOP principles. I have several classes in my project, and some of them need to access run-time configuration parameters. These ...
14
votes
4answers
793 views

APIs and functional programming

From my (admittedly limited) exposure to functional programming languages, such as Clojure, it seems that encapsulation of data has a less important role. Usually various native types such as maps or ...
2
votes
2answers
150 views

Acceptable design to use public member objects in composition?

Say I have a large class called Root, which has a lot of members & functions: class Root { public: void func1(); // operates on a and b void func2(); ... private: A a; ...
1
vote
2answers
84 views

What is “recorded” relationship in a class diagram? [closed]

Composite aggregates Part, Container contains Content, and Recorder records. Recorded are all very common relationships between classes in a class diagram. Creator suggests that the enclosing ...
3
votes
3answers
231 views

How to “program to an interface”

I've read these questions: Understanding "programming to an interface" What is the point of an interface? Does it always make sense to "program to an interface" in Java? I don'...
1
vote
0answers
81 views

WMC Calculation in CK Metrics Suite

I have two classes C1 and C2. C1 has 2 methods and C2 has 3 methods each of complexity value 1. C2 inherits from C1. So, I know C2 has 2+3=5 methods in all. The question is, should I take C2 to have 5 ...
2
votes
2answers
200 views

What is meant by reuse of inheritance?

A 2013 study of 93 open source Java programs (of varying size) found that While there is [no] huge opportunity to replace inheritance with composition (...), the opportunity is significant (...
-2
votes
1answer
113 views

Should objects with different properties (not behaviour) have different types?

I see a lot of classes that look like: class Student extends Model { public string major; public string minor; } class Employee extends Model { public string department; public ...
4
votes
3answers
252 views

Alternatives to Singletons for caching lists of data?

In my project, I have an abstract Cache class that allows me to populate a series of lists that globally persist throughout my application. These cache objects are thread-safe and can be manipulated ...
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 ...
0
votes
1answer
73 views

How to periodically serialise object's state and deserialise on initialisation in Python?

We're designing an application that is supposed to monitor a system for certain events, email interested parties to prompt them to take action when relevant and parse their replies. The application ...
1
vote
3answers
261 views

Function Overloading in Python

My book says that function overloading is not possible in python but it asks me questions like: WAP to find out the volume of a cube,cuboid and cylinder using function overloading. Do I have to ...
3
votes
2answers
109 views

Best practice in helper/util methods: IoC container or static methods?

So I'm developing an application which is using an IoC container. Now I need some helper methods for array manipulation like set, get, etc. I see two possible ways to go: Using a class with static ...
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 ...
36
votes
5answers
2k views

How is defining that a method can be overridden a stronger commitment than defining that a method can be called?

From : http://www.artima.com/lejava/articles/designprinciples4.html Erich Gamma: I still think it's true even after ten years. Inheritance is a cool way to change behavior. But we know that it's ...
1
vote
1answer
94 views

Setting up my inheritance model?

I'm working on refactoring a synchronization web app that our company uses. Currently it's merely a set of controllers that fire up a set of helpers that go through a long chain of if-else type ...