Inheritance in Dart

What is Inheritance?

Inheritance lets a class (child/subclass) inherit all the fields and methods of another class (parent/superclass). The child class can then add its own members or override inherited ones. This promotes code reuse and establishes an "is-a" relationship.

extends Keyword

class Animal {
  String name;
  Animal(this.name);

  void eat() => print('$name is eating.');
  void breathe() => print('$name is breathing.');
}

class Dog extends Animal {
  String breed;
  Dog(String name, this.breed) : super(name);

  void bark() => print('$name says: Woof!');
}

class Cat extends Animal {
  Cat(String name) : super(name);
  void meow() => print('$name says: Meow!');
}

super Keyword

super refers to the parent class. Use it to call the parent constructor or access parent methods:

Dog rex = Dog('Rex', 'German Shepherd');
rex.eat();    // Rex is eating.    (inherited from Animal)
rex.breathe(); // Rex is breathing. (inherited)
rex.bark();   // Rex says: Woof!  (Dog's own method)

Overriding Methods

A subclass can redefine a parent method using @override:

class Animal {
  String name;
  Animal(this.name);
  void speak() => print('$name makes a sound.');
}

class Dog extends Animal {
  Dog(String name) : super(name);

  @override
  void speak() => print('$name says: Woof!');
}

class Cat extends Animal {
  Cat(String name) : super(name);

  @override
  void speak() => print('$name says: Meow!');
}

Full Example

class Shape {
  String color;
  Shape(this.color);

  double area() => 0;
  void describe() => print('A $color shape with area $${area().toStringAsFixed(2)}');
}

class Circle extends Shape {
  double radius;
  Circle(String color, this.radius) : super(color);

  @override
  double area() => 3.14159 * radius * radius;
}

class Rectangle extends Shape {
  double width, height;
  Rectangle(String color, this.width, this.height) : super(color);

  @override
  double area() => width * height;
}

void main() {
  var shapes = [
    Circle('red', 5),
    Rectangle('blue', 4, 6),
  ];

  for (var s in shapes) {
    s.describe();
  }
}

A red shape with area 78.54
A blue shape with area 24.00

🧠 Quiz

Summary

Inheritance uses extends to create a child class that reuses parent fields and methods. Use super() to call the parent constructor. Override methods with @override to customize behavior in subclasses. Dart supports single inheritance only (one parent per class).