Dart LanguageIntermediate30 XP4 min read

What is the difference between abstract class, interface, and mixin in Dart?

TL;DR: Every Dart class is implicitly an interface. abstract classes define contracts + optional implementations; mixins share behavior without inheritance; class + implements = pure contract with no shared implementation.

Full Answer

Aspect	Construct	Use when
abstract class	Partial implementation, some methods abstract	Template method pattern, base classes
implements	Pure contract — must implement everything	Polymorphism, dependency inversion
mixin	Reusable behavior, no is-a relationship	Adding capabilities orthogonally
interface class	Dart 3: explicit interface, no implementation	Public API contracts

Code Examples

dartAbstract class vs implements vs mixin

Output

Dog breathes
[Dog] About to bark
Woof!
{type: dog, name: Dog}

Interview Tip

💡

Dart 3 introduced 'interface class' keyword to explicitly mark a class as interface-only (no mixin use, no extension). This makes API design clearer.

#abstract-class#interface#mixin#implements#extends

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