extends

Learn to inherit from a base class with extends.

extends

In Dart a class inherits from another with the extends keyword. The class being inherited is the base class; the inheriting one is the derived class.

Example: class Dog extends Animal { ... }. Here Dog inherits all public members of Animal. The subclass can call the superclass methods on itself and add new methods or fields. Dart uses single inheritance: each class extends at most one class. To combine behavior from many sources you use mixins, which we will see later.

Inherited methods

A subclass can use the methods of its base class without redefining them. The call goes through its own instance and is automatically routed to the base class.

Example: suppose Animal has void breathe() { print('Breathing'); }. After Dog extends Animal, Dog instances can call breathe() directly: Dog().breathe(). No extra code is needed in the subclass. This reduces duplication: shared behavior lives in the base class and subclasses share it.

Exercise Define Dog with extends

Keep the existing Animal class. Define a class named Dog that inherits from Animal; add a Dog(); constructor. In main, create an instance with var d = Dog(); and call d.breathe().

Show example solution

class Animal {
  void breathe() {
    print('Breathing');
  }
}

class Dog extends Animal {
  Dog();
}

void main() {
  var d = Dog();
  d.breathe();
}

Test yourself

Which is a valid extends declaration?
- class Dog inherits Animal { }
- class Dog implements Animal { }
- class Dog extends Animal { }
- class Dog : Animal { }
Show answer

class Dog extends Animal { } — extends is the Dart keyword for inheritance.

Add the extends keyword

class Dog ____ Animal {
  Dog();
}

Show answer

class Dog extends Animal {
  Dog();
}

Match the inheritance parts

Animal

Base class
Dog

Derived class
breathe

Inherited method

Next lesson: super

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