Override

Learn to redefine methods with @override.

@override

A subclass can redefine a method of its base class. This is called override and Dart suggests marking it with the @override annotation.

Example: class Dog extends Animal { @override void speak() { print('Woof woof'); } }. Here Dog replaces Animal's speak with its own version. The @override annotation is not a comment; it tells the compiler your intent. A wrong signature gives an error, so it is a safe marker. The call dispatches by the instance type: Dog().speak() prints 'Woof woof'.

Polymorphism

A base class reference can hold subclass instances. The call dispatches by the actual type of the instance; this behavior is called polymorphism.

Example: Animal a = Dog(); a.speak();. Here a has the static type Animal and the dynamic type Dog. The speak() call runs the Dog version. This lets a list hold different subclass instances and each runs its own speak() version. Polymorphism keeps code flexible and extensible.

Exercise Override speak in Dog

Keep the existing Animal class. Add an @override void speak() { print('Woof woof'); } method to the Dog class. In main, create an instance with var d = Dog(); and call d.speak().

Show example solution

class Animal {
  void speak() {
    print('Makes a sound');
  }
}

class Dog extends Animal {
  Dog();
  @override
  void speak() {
    print('Woof woof');
  }
}

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

Test yourself

Match the override parts

@override

Annotation
speak

Redefined method
Dog

Subclass

Add the @override annotation

class Dog extends Animal {
  ____
  void speak() {
    print('Woof woof');
  }
}

Show answer

class Dog extends Animal {
  @override
  void speak() {
    print('Woof woof');
  }
}

What does Animal a = Dog(); a.speak(); print?
- Woof woof
- Nothing
- Makes a sound
- Throws an error
Show answer

Woof woof — Polymorphism runs the Dog version.

Next lesson: abstract

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