Dart – Concept of Inheritance

In Dart, one class can inherit another class i.e dart can create a new class from an existing class. We make use of extend keyword to do so.

Terminology:

• Parent Class: It is the class whose properties are inherited by the child class. It is also known as a base class or superclass.
• Child Class: It is the class that inherits the properties of the other classes. It is also known as a deprived class or subclass.

class parent_class{
...
}

class child_class extends parent_class{
...
}

Example 1: Example of Single Inheritance in the dart. 

Dart

// Dart program to show the single inheritance

// Creating parent class
class Gfg{

  // Creating a function
  void output(){
    print("Welcome to gfg!!\nYou are inside output function.");
  }
}

// Creating Child class
class GfgChild extends Gfg{
  // We are not defining
  // any thing inside it...
}
void main() {
  // Creating object of GfgChild class
  var geek = new GfgChild();

  // Calling function
  // inside Gfg(Parent class)
  geek.output();
}

Output:

Welcome to gfg!!
You are inside output function.

Types of Inheritance:

1. Single Inheritance: This inheritance occurs when a class inherits a single-parent class.
2. Multiple Inheritance: This inheritance occurs when a class inherits more than one parent class. Dart doesn’t support this.
3. Multi-Level Inheritance: This inheritance occurs when a class inherits another child class.
4.  Hierarchical Inheritance: More than one classes have the same parent class.

Important Points: 

1. Child classes inherit all properties and methods except constructors of the parent class.
2. Like Java, Dart also doesn’t support multiple inheritance.

Example 2:

Dart

// Dart program for multilevel interitance

// Creating parent class
class Gfg{

  // Creating a function
  void output1(){
    print("Welcome to gfg!!\nYou are inside the output function of Gfg class.");
  }
}

// Creating Child1 class
class GfgChild1 extends Gfg{

  // Creating a function
  void output2(){
    print("Welcome to gfg!!\nYou are inside the output function of GfgChild1 class.");
  }
}

// Creating Child2 class
class GfgChild2 extends GfgChild1{
  // We are not defining
  // any thing inside it...
}

void main() {
  // Creating object
  // of GfgChild class
  var geek = new GfgChild2();

  // Calling function
  // inside Gfg
  //(Parent class of Parent class)
  geek.output1();

  // Calling function
  // inside GfgChild
  // (Parent class)
  geek.output2();
}

Output:

Welcome to gfg!!
You are inside the output function of Gfg class.
Welcome to gfg!!
You are inside the output function of GfgChild1 class.

Example 3: Hierarchical inheritance.  

Dart

// Dart program for Hierarchical inheritance

// Creating parent class
class Gfg{

  // Creating a function
  void output1(){
    print("Welcome to gfg!!\nYou are inside output function of Gfg class.");
  }
}

// Creating Child1 class
class GfgChild1 extends Gfg{
  // We are not defining
  // any thing inside it...
}

// Creating Child2 class
class GfgChild2 extends Gfg{

  // We are not defining
  // any thing inside it...
}

void main() {
  // Creating object
  // of GfgChild1 class
  var geek1 = new GfgChild1();

  // Calling function
  // inside Gfg(Parent class)
  geek1.output1();

  // Creating object of
  // GfgChild1 class
  var geek2 = new GfgChild2();

  // Calling function
  // inside Gfg(Parent class)
  geek2.output1();
}

Output:

Welcome to gfg!!
You are inside output function of Gfg class.
Welcome to gfg!!
You are inside output function of Gfg class.