What's variant better? SOLID - SRP and interfaces

Question

What variant is better? SOLID - SRP or the one with the interface?

class Some {
    private final IValidator validator;
    public Some(IValidator validator) {
        this.validator = validator;
    }

    public void doSomething() {
        if (validator.validate(data));
            // do something
    }
}

OR

class Some {
    private final Validator validator = new Validator();

    public void doSomething() {
        if (validator.validate(data));
            // do something
    }
}

Validator is used once.

Both doesn't compile.. I suppose it's `private final IValidator validator;` and `private final Validator validator`? — almightyGOSU, Jun 15 '15 at 12:14
Both compiles succesfully. Do I need interface for Validator class? What does say SRP principe? — Алексей Мальченко, Jun 15 '15 at 12:21
You should probably worry about how `private final Validator = new Validator();` doesn't work, before thinking about SOLID.. -_- — almightyGOSU, Jun 15 '15 at 12:25
I'd always prefer the interface. This way you can easily switch to a different implementation of the interface later on. — Kris, Jun 15 '15 at 12:31
Title is misleading as this question is not about SOLID. If SRP is Single Responsibility Principle, you already got that covered in S of SOLID. — John, Jun 15 '15 at 12:33
If anything, this is more a question about the 'D' of SOLID — Dependency inversion — that Single Responsible principle. — anotherdave, Jun 19 '15 at 17:03

score 2 · Accepted Answer · answered Jun 15 '15 at 12:43

By writing Validator validator = new Validator() you are actually increasing the coupling of your code, which is definitely against SOLID.

Like @Kris told in the comments, the best way is to use the interface instead of the actual implementation - this actually corresponds more with the polymorphism and already after it it is about SOLID.

What's variant better? SOLID - SRP and interfaces

1 Answers1