Linked Questions

My sample program like below; public class Animal { public virtual string MakeSound() { return "General Sound"; } } public class Dog : Animal {...

i'm trying to understand the basics of polymorphism. I do understand why it could be useful to assign a superclass to a sub class or a sub to a super. what i don't understand quite well is the logic ...

As I've read the substitution of objects of a concrete type by instances of a subclass of that concrete type must preserve a program's correctness, a program's invariants. I'd like to know what ...

What does the expression "Turing Complete" mean? Can you give a simple explanation, without going into too many theoretical details?

I have a class Animal, and its subclass Dog. I often find myself coding the following lines: if (animal is Dog) { Dog dog = animal as Dog; dog.Name; ... } For the variable Animal ...

The word seems to get used in a number of contexts. The best I can figure is that they mean a variable that can't change. Isn't that what constants/finals (darn you Java!) are for?

What is the difference between syntax and semantics in programming languages (like C, C++)?

A lot of people seem to agree, that the Singleton pattern has a number of drawbacks and some even suggest avoiding the pattern entirely. There's an excellent discussion here. Please direct any ...

I need some resources that talk about how to design your software to be extensible, i.e. so that other people can write add-ons/plug-ins that adds functionality to it. What do you recommend? Any ...

My understanding of the Liskov substitution principle is that some property of the base class that is true or some implemented behaviour of the base class, should be true for the derived class as well....

I always thought functions and methods were the same, until I was learning Swift through the "Swift Programming Language" eBook. I found out that I cannot use greet("John", "Tuesday") to call a ...

For a unit test, I need to mock several dependencies. One of the dependencies is a class which implements an interface: public class DataAccessImpl implements DataAccess { ... } I need to set up ...

The Liskov Substitution Principle states that a subtype should be substitutable for that type (without altering the correctness of the program). Can someone please provide an example of this principle ...

When I design classes and have to choose between inheritance and composition, I usually use the rule of thumb: if the relationship is "is-a" - use inheritance, and if the relationship is "has-a" - use ...

In the comments of this answer it is stated that "checking whether the object has implemented the interface , rampant as it may be, is a bad thing" Below is what I believe is an example of this ...

Can anyone explain the concept of covariance and contravariance in programming language theory?

I have seen many people in the Scala community advise on avoiding subtyping "like a plague". What are the various reasons against the use of subtyping? What are the alternatives?

There are claims that Scala's type system is Turing complete. My questions are: Is there a formal proof for this? How would a simple computation look like in the Scala type system? Is this of any ...

Is there any core difference between Liskov Substitution Principle (LSP) and Interface Segregation Principle (ISP)? Ultimately, both are vouching for designing the interface with common ...

I have seen few Pet and Dog type examples for this type of basic question here and here, but they do not make sense to me, here is why. Suppose we have the following class structure class Pet {}; ...

Here's a couple of snippets: Overriding constructor method has an extra parameter. class Cat { function __construct() {} } class Lion extends Cat { function __construct($param) {} } ...

I understand that virtual methods allow a derived class to override methods inherited from a base class. When is it appropriate/inappropriate to use virtual methods? It's not always known whether or ...

I apologize for the subjectiveness of this question, but I am a little stuck and I would appreciate some guidance and advice from anyone who's had to deal with this issue before: I have (what's ...

I am having trouble with the concept of interfaces interacting with polymorphic types (or even polymorphic interfaces). I'm developing in C# and would appreciate answers staying close to this ...

List("a").contains(5) Because an Int can never be contained in a list of String, this should generate an error at compile-time, but it does not. It wastefully and silently tests every String ...

I have a situation where I need to modify the super class method to have a subclass specific logic, but the methods logic is same for all other subclasses. I have two options: 1) make the method ...

I have following class: public class Publisher<T> { private static final Class[] SUPPORTED_CLASSES = new Class[]{T1.class, T2.class}; public Publisher() { if(Arrays.asList(...

Is it possible to wrap text around a non rectangular image? I want text around maps of different countries to wrap around the country's shape in such a way that the text always keeps the same ...

What is the best way to unit test subclasses? Let's assume there's a base class for which I've already written tests and there are some number of subclasses that override some of the parent's ...

I want to have a certain kind of std::vector that cannot have more than const int MAX_LENGTH elements. I understand that I cannot override std::vector non-virtual functions, which I'd need to do to ...