Inheritance in Dart

Let's forget programming for a moment and talk about real life. What do we understand when someones says the word inheritance?

Inheritance is the process of passing on properties from one generation to another. For example, a child inherits the properties of his/her parents and grandparents which continues this from generation to generation.

Before we dive into inheritance in Dart, let's first understand the keyword extends, this and super in Dart.

This keywords are very important to understand and implement inheritance in Dart.

What is Inheritance in Dart Programming?

In programming, inheritance is the process of passing on properties from one class to another.

The class that passes on the properties is called the parent class or the superclass. The class that inherits the properties is called the child class or the subclass.

Inheritance is a very important concept in object oriented programming. It allows us to reuse code and also to add more features to a class without modifying it.

Example

Let's look at an example of inheritance in Dart.

class Animal {
  String name;
  int age;
 
  Animal(this.name, this.age);
 
  void eat() {
    print('$name is eating');
  }
 
  void sleep() {
    print('$name is sleeping');
  }
}
 
class Dog extends Animal {
  Dog(String name, int age) : super(name, age);
 
  void bark() {
    print('$name is barking');
  }
}
 
void main() {
  var dog = Dog('Bruno', 2);
  dog.eat();
  dog.sleep();
  dog.bark();
}

Output

Bruno is eating
Bruno is sleeping
Bruno is barking

Types of Inheritance

There are different types of inheritance in Dart. Dart supports the following types of inheritance.

• Single Inheritance
• Multiple Inheritance
• Multilevel Inheritance

Single Inheritance in Dart

Single inheritance is the process of inheriting properties from a single parent class. This means, If there are class A and class B, and class B inherits from class A, then it is called single inheritance.

Example

class Animal {
  String name;
  int age;
 
  Animal(this.name, this.age);
 
  void eat() {
    print('$name is eating');
  }
 
  void sleep() {
    print('$name is sleeping');
  }
}
 
class Dog extends Animal {
  Dog(String name, int age) : super(name, age);
 
  void bark() {
    print('$name is barking');
  }
}
 
void main() {
  var dog = Dog('Bruno', 2);
  dog.eat();
  dog.sleep();
  dog.bark();
}

This is an example of single inheritance. The class Dog inherits from the class Animal. Let's take the output of code.

Output

Bruno is eating
Bruno is sleeping
Bruno is barking

Multi-level Inheritance in Dart

Multi-level inheritance is the process of inheriting properties from a parent class and then inheriting properties from the child class.

This means, If there are class A, class B and class C, and class B inherits from class A and class C inherits from class B, then it is called multi-level inheritance.

Example

 
class Animal {
  String name;
  int age;
 
  Animal(this.name, this.age);
 
  void eat() {
    print('$name is eating');
  }
 
  void sleep() {
    print('$name is sleeping');
  }
}
 
class Dog extends Animal {
  Dog(String name, int age) : super(name, age);
 
  void bark() {
    print('$name is barking');
  }
}
 
class Human extends Animal { 
    Human(String name, int age) : super(name, age);
    
    void speak() {
        print('$name is speaking');
    }
 
}
 
void main() {
  var dog = Dog('Bruno', 2);
  dog.eat();
  dog.sleep();
  dog.bark();
  
  var human = Human('John', 25);
  human.eat();
  human.sleep();
  human.speak();
}

This is an example of multi-level inheritance. The class Dog inherits from the class Animal and the class Human inherits from the class Animal. Let's take the output of code.

Output

Bruno is eating
Bruno is sleeping
Bruno is barking

John is eating
John is sleeping
John is speaking

Multilevel Inheritance in Dart

Multilevel inheritance is the process of inheriting properties from a parent class and then inheriting properties from the child class.

This means, If there are class A, class B and class C, and class B inherits from class A and class C inherits from class B, then it is called multi-level inheritance.

Example

class Animal {
  String name;
  int age;
 
  Animal(this.name, this.age);
 
  void eat() {
    print('$name is eating');
  }
 
  void sleep() {
    print('$name is sleeping');
  }
}
 
class Dog extends Animal {
  Dog(String name, int age) : super(name, age);
 
  void bark() {
    print('$name is barking');
  }
} 
 
class Breed extends Dog {
  String breed;
 
  Breed(String name, int age, this.breed) : super(name, age);
 
  void displayBreed() {
    print('$name is a $breed');
  }
} 
 
void main() {
  var dog = Breed('Bruno', 2, 'Labrador');
  dog.eat();
  dog.sleep();
  dog.bark();
  dog.displayBreed();
}

Output

Bruno is eating
Bruno is sleeping
Bruno is barking
Bruno is a Labrador

Overriding Methods in Dart

Overriding methods is the process of redefining a method of a parent class in the child class.

This means that if there is a method in the parent class and the child class has the same method, then the method of the child class will be called while inheritance of any parent classes.

Example

class Animal {
  String name;
  int age;
 
  Animal(this.name, this.age);
 
  void eat() {
    print('$name is eating');
  }
 
  void sleep() {
    print('$name is sleeping');
  }
}
 
class Dog extends Animal {
  Dog(String name, int age) : super(name, age);
 
  void bark() {
    print('$name is barking');
  }
 
  @override
  void sleep() {
    print('$name is sleeping');
  }
} 
 
 
void main() {
  var dog = Dog('Bruno', 2);
  dog.eat();
  dog.sleep();
  dog.bark();
}

Output

Bruno is eating
Bruno is sleeping
Bruno is barking

Overriding Properties in Dart

Overriding properties is the process of redefining a property of a parent class in the child class.

This means that if there is a property in the parent class and the child class has the same property, then the property of the child class will be called while inheritance of any parent classes.

Example

class Animal { 
 
final String name; 
  
final String age ; 
  
Animal(this.name, this.age); 
 
 } 
 
 
class Dog extends Animal {  
  
  
  
  final String name; 
  
  
  Dog(this.name, String age) : super("$name-1", age);  
  
} 
 
void main() {
  var dog = Dog('Bruno', 2);
  print(dog.name);
}

Output

Bruno

You can notice that the output that came is Bruno and not Bruno-1. This is because we have overridden the property name in the child class.