203
votes
Accepted
Should we design our code from the beginning to enable unit testing?
Reluctance to modify code for the sake of testing shows that a developer hasn't understood the role of tests, and by implication, their own role in the organization.
The software business revolves ...
- 111k
165
votes
Accepted
How do I ensure that interface implementations are implemented in the manner I expected?
Instead of returning an int, return a value object that has the validation hard-coded. This is a case of primitive obsession and its fix.
// should be class, not struct as struct can be created ...
- 38.2k
82
votes
Should I still follow "programming to an interface not implementation" even if I think using concrete class members is the simpler solution?
Programming to an interface means that you should focus on what the code does, not how it is actually implemented. See Telastyn's answer to Understanding “programming to an interface”. Interface ...
- 2,040
75
votes
Should we design our code from the beginning to enable unit testing?
It's not as simple as you might think. Let's break it down.
Writing unit tests is definitely a good thing.
BUT!
Any change to your code can introduce a bug. So changing the code without a good ...
- 84.4k
55
votes
Accepted
In "I don’t want my users knowing that I’m handing them an interface.", why is the severity "I don’t want" instead of "Users don't need to know"?
why would the post use the tone "I don’t want" in "I don’t want my users knowing that I’m handing them an interface."
This is a cite from the "Clean Code" book by Robert ...
- 220k
51
votes
Is it ok to inherit a class without adding anything to the child, to respect the Open Closed principle?
No. Emphatic no.
Unless I misunderstood you, the question is to subclass for a different behavior, but actually not have the behavior itself. Instead an outside actor checks the exact type and does ...
- 12.4k
49
votes
Should I still follow "programming to an interface not implementation" even if I think using concrete class members is the simpler solution?
"Programming to an interface" does not require the language keyword interface. It means you care about what promises the type provides about it's behaviour.
You don't care how java.lang....
- 12.4k
45
votes
Is it Good Practice to Only Expose Interfaces
As is the nature of using interfaces, this decouples my users from being concerned with how I variously decide to refactor the implementations.
Let's take a step back and make sure we understand what ...
- 30.9k
40
votes
Accepted
Implementation of pure abstract classes and interfaces
In C# and Java implementations, the objects typically have a single pointer to its class. This is possible because they are single-inheritance languages. The class structure then contains the vtable ...
- 136k
39
votes
Accepted
Pass object twice to same method or consolidate with combined interface?
No, this is perfectly fine. It merely means that the API is over-engineered with regards to your current application.
But that doesn't prove that there will never a use case in which the data source ...
- 111k
38
votes
Accepted
What does the author mean by casting the interface reference to any implementation?
Abstracting your class into an interface is something you should consider if and only if you intend on writing other implementations of said interface or the strong possibility of doing so in the ...
- 22.9k
38
votes
In C#, is there a way to enforce behavior coupling in interface methods or is the fact that I am trying to do that a design smell?
What you are looking for is a well-known approach called Design by Contract. It was supported directly in the framework in version 4.0.
DISCLOSURE: Be careful when adding code contracts to a new ...
- 220k
37
votes
In a fluent interface with "with", is cloning expected?
Looking at this code I’d have no idea. Semantically you did say it’s another pizza. But since this is of type Pizza and not a PizzaBuilder that gives you a pizza object only after you call the build ...
- 120k
35
votes
Accepted
In C#, is there a way to enforce behavior coupling in interface methods or is the fact that I am trying to do that a design smell?
Well, first of all, let's tweak your interface a bit.
public interface IComponent
{
void Enable();
void Disable();
bool IsEnabled { get; }
}
Now then. What could potentially go wrong ...
- 201k
33
votes
Why just "interface segregation principle" but not "method segregation principle"?
The principle of Low Coupling/High Cohesion states that functionality that is closely related and interdependent should be in the same class or module, and functionality that is not closely related ...
- 62.3k
32
votes
Accepted
Does it make sense to define an interface if I already have an abstract class?
Yes, because C# doesn't allow multiple inheritance except with interfaces.
So if I have a class which is both a TypeNameMapper and SomethingelseMapper I can do:
class MultiFunctionalClass : ...
- 84.4k
32
votes
In C#, is there a way to enforce behavior coupling in interface methods or is the fact that I am trying to do that a design smell?
You're asking too much of C# Interfaces.
C# Interfaces are contracts. They say what pack of methods a given class implements, and they guarantee that those methods will be there if someone calls them....
- 2,166
30
votes
What does the author mean by casting the interface reference to any implementation?
The accepted answer is correct and very useful, but I would like to briefly address specifically the line of code you asked about:
ISomeClass myClass = new SomeClass();
Broadly speaking, this isn't ...
- 444
27
votes
In a fluent interface with "with", is cloning expected?
No, the naming prefix with does not tell if it's cloning or mutating. There are popular examples of fluent interfaces using a mutating with and some language-specific conventions (e.g. Java) that ...
- 82.2k
25
votes
How do I ensure that interface implementations are implemented in the manner I expected?
To complement the other answers, I'd like to partially comment on the following note in the OP by providing a broader context:
An interface seems like a good concept, if only I could also specify ...
- 389
25
votes
Accepted
OOP Design considering no modifications to existing design
You could use the Decorator Pattern to add additional responsibilities to an Animal without subclassing.
public interface Animal {
void eat();
}
public class Lion implements Animal {
public ...
- 39.6k
25
votes
In "I don’t want my users knowing that I’m handing them an interface.", why is the severity "I don’t want" instead of "Users don't need to know"?
Are you sure you understood the answer to the question you linked correctly? Because the answers agreed that putting an I in front of interfaces if that is the convention in your language of choice is ...
- 9,230
24
votes
Accepted
How does encapsulation actually work?
Coupling
ClassA relies upon the interface only, delegating this responsibility of passing the classB object elsewhere
This is the idea. If ...
- 9,261
23
votes
How do I ensure that interface implementations are implemented in the manner I expected?
You're trying to design by contract, where that contract is that the return value must be greater than 5. Unfortunately, if you're relying on an interface, the only contract you have is the method ...
- 506
23
votes
Accepted
Where should interfaces be used?
I don't think there's really a simple answer that can do a substantially better job than the statements of the principles and practices that you've already encountered.
I know you're aware of this on ...
- 9,490
23
votes
Accepted
Is it Good Practice to Only Expose Interfaces
While this may be an opinion-based question, and the real answer is the same as with many endeavors in software design and development ("it depends"), I'm going to say yes, do not expose ...
- 6,031
22
votes
In C#, is there a way to enforce behavior coupling in interface methods or is the fact that I am trying to do that a design smell?
State transitions can be represented by separate interfaces per state:
public interface IEnabledComponent
{
IDisabledComponent ToDisabled();
}
public interface IDisabledComponent
{
...
- 62.3k
22
votes
How does encapsulation actually work?
Your confusion is probably caused by focusing on meaningless class and interface names, with no real usage scenario behind it. So better let us make a concrete example (I prefer C#, but it is not ...
- 220k
22
votes
OOP Design considering no modifications to existing design
Perfect time for composition. Create a new implementation of Animal that does the counting, but also delegates the "real" function. Like this:
public final class LoggingAnimal implements ...
- 12.4k
18
votes
Accepted
Java interface for comments only. Good practice?
No, you should not introduce documentation-only interfaces. This removes one of the big advantages of Javadoc: that the docs are right next to the code, which makes it easier to keep them in sync.
...
- 136k
Only top scored, non community-wiki answers of a minimum length are eligible