What are the differences between an abstract class and a mixin in Dart?

Abstract class:

• Cannot be instantiated directly.
• Can contain abstract methods (without implementation) and implemented methods.
• Classes inherit from an abstract class using the extends keyword.
• A class can only inherit from one class (single inheritance).

Mixin:

• Cannot be instantiated directly.
• Cannot have constructors.
• Can contain implemented methods, but cannot have abstract methods (until Dart 2.1, where abstract mixins appeared).
• Classes use the functionality of mixins with the with keyword.
• A class can use multiple mixins.
• Used for code reuse and adding functionality to classes without inheritance. Essentially, it allows "mixing in" behavior.

Example of an abstract class:

abstract class Animal {
  void makeSound(); // Abstract method
  void eat() {
    print('Eating...');
  }
}

class Dog extends Animal {
  @override
  void makeSound() {
    print('Woof!');
  }
}

Example of a mixin:

mixin CanJump {
  void jump() {
    print('Jumping!');
  }
}

class Cat with CanJump { }

Comparison in tabular form:

Attribute	Abstract Class	Mixin
Instantiation	No	No
Constructor	Can have	Cannot have
Abstract methods	Can have	Cannot have (until Dart 2.1)
Implemented methods	Can have	Can have
Usage	extends	with
Inheritance/Usage	Single inheritance	Multiple usage
Purpose	Define a common contract	Code reuse, adding behavior