Inheritance Of Constructor in Dart

Introduction

In this section, you will learn about inheritance of constructor in Dart programming language with the help of examples. Before learning about inheritance of constructor in Dart, you should have a basic understanding of the constructor and inheritance in Dart.

What Is Inheritance Of Constructor In Dart?

Inheritance of constructor in Dart is a process of inheriting the constructor of the parent class to the child class. It is a way of reusing the code of the parent class.

Example 1: Inheritance Of Constructor In Dart

In this example below, there is class named Laptop with a constructor. There is another class named MacBook which extends the Laptop class. The MacBook class has its own constructor.

class Laptop {
  // Constructor
  Laptop() {
    print("Laptop constructor");
  }
}

class MacBook extends Laptop {
  // Constructor
  MacBook() {
    print("MacBook constructor");
  }
}

void main() {
  var macbook = MacBook();
}

Laptop constructor
MacBook constructor

Example 2: Inheritance Of Constructor With Parameters In Dart

In this example below, there is class named Laptop with a constructor with parameters. There is another class named MacBook which extends the Laptop class. The MacBook class has its own constructor with parameters.

class Laptop {
  // Constructor
  Laptop(String name, String color) {
    print("Laptop constructor");
    print("Name: $name");
    print("Color: $color");
  }
}

class MacBook extends Laptop {
  // Constructor
  MacBook(String name, String color) : super(name, color) {
    print("MacBook constructor");
  }
}

void main() {
  var macbook = MacBook("MacBook Pro", "Silver");
}

Laptop constructor
Name: MacBook Pro
Color: Silver
MacBook constructor

Example 3: Inheritance Of Constructor

In this example below, there is class named Person with properties name and age. There is another class named Student which extends the Person class. The Student class has additional property rollNumber. Lets see how to create a constructor for the Student class.

class Person {
  String name;
  int age;

  // Constructor
  Person(this.name, this.age);
}

class Student extends Person {
  int rollNumber;

  // Constructor
  Student(String name, int age, this.rollNumber) : super(name, age);
}

void main() {
  var student = Student("John", 20, 1);
  print("Student name: ${student.name}");
  print("Student age: ${student.age}");
  print("Student roll number: ${student.rollNumber}");

}

Student name: John
Student age: 20
Student roll number: 1

Example 4: Inheritance Of Constructor With Named Parameters In Dart

In this example below, there is class named Laptop with a constructor with named parameters. There is another class named MacBook which extends the Laptop class. The MacBook class has its own constructor with named parameters.

class Laptop {
  // Constructor
  Laptop({String name, String color}) {
    print("Laptop constructor");
    print("Name: $name");
    print("Color: $color");
  }
}

class MacBook extends Laptop {
  // Constructor
  MacBook({String name, String color}) : super(name: name, color: color) {
    print("MacBook constructor");
  }
}

void main() {
  var macbook = MacBook(name: "MacBook Pro", color: "Silver");
}

Laptop constructor
Name: MacBook Pro
Color: Silver
MacBook constructor

Example 5: Calling Named Constructor Of Parent Class In Dart

In this example below, there is class named Laptop with one default constructor and one named constructor. There is another class named MacBook which extends the Laptop class. The MacBook class has its own constructor with named parameters. You can call the named constructor of the parent class using the super keyword.

class Laptop {
  // Default Constructor
  Laptop() {
    print("Laptop constructor");
  }

  // Named Constructor
  Laptop.named() {
    print("Laptop named constructor");
  }
}

class MacBook extends Laptop {
  // Constructor
  MacBook() : super.named() {
    print("MacBook constructor");
  }
}

void main() {
  var macbook = MacBook();
}

Laptop named constructor
MacBook constructor

Video

Watch our video on inheritance of constructor in Dart.