@override

Learn the @override annotation.

@override in depth

@override states that a subclass method redefines a superclass method. For example inside class Cat extends Animal you add @override to the String toString() method.

The annotation is not required but Dart recommends it. If you write a wrong signature the compiler warns thanks to @override; a warning appears when no matching method exists in the superclass.

It is commonly used to override Object methods such as toString, hashCode and noSuchMethod.

Exercise Cat and @override

Define an Animal class with a String name field and an Animal(this.name) constructor. Write a Cat extends Animal subclass with a Cat(String name) : super(name) constructor. Add a @override method String toString() => 'Cat $name'. In main print a Cat('Luna') instance with print.

Show example solution

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

class Cat extends Animal {
  Cat(String name) : super(name);
  @override
  String toString() => 'Cat $name';
}

void main() {
  print(Cat('Luna'));
}

Analysis and @override

When you write @override Dart analysis looks for a matching method in the superclass. If it finds none it warns. This stops you from accidentally creating a new method through a typo.

For example if you write toStrring, without @override this becomes a new method; with @override analysis catches it.

A good habit: always write @override when redefining a superclass method. IDEs add it automatically.

Test yourself

The @override tag

class Cat extends Animal {
  @____
  String toString() => 'Kedi';
}

Show answer

class Cat extends Animal {
  @override
  String toString() => 'Kedi';
}

When is @override written?
- When adding a new method
- When deleting a field
- When redefining a superclass method
- When setting up a loop
Show answer

When redefining a superclass method — @override is written when redefining a superclass method.
What happens if you omit @override?
- The compiler always errors
- The program does not compile
- The method does not run
- A wrong signature warning is missed
Show answer

A wrong signature warning is missed — @override catches a wrong signature, otherwise the warning is missed.

Next lesson: @deprecated

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