Default Constructor in Dart

Default Constructor

The constructor which is automatically created by the dart compiler if you don’t create a constructor is called a default constructor. A default constructor has no parameters. A default constructor is declared using the class name followed by parentheses ().

Example 1: Default Constructor In Dart

In this example below, there is a class Laptop with two properties: brand, and price. Lets create constructor with no parameter and print something from the constructor. We also have an object of the class Laptop called laptop.

class Laptop {
  String? brand;
  int? price;

  // Constructor
  Laptop() {
    print("This is a default constructor");
  }
}

void main() {
  // Here laptop is object of class Laptop.
  Laptop laptop = Laptop();
}

This is a default constructor

Example 2: Default Constructor In Dart

In this example below, there is a class Student with four properties: name, age, schoolname and grade. The default constructor is used to initialize the values of the school name. The reason for this is that the school name is the same for all the students. We also have an object of the class Student called student. The default constructor is called automatically when you create an object of the class.

class Student {
  String? name;
  int? age;
  String? schoolname;
  String? grade;

  // Default Constructor
  Student() {
    print(
        "Constructor called"); // this is for checking the constructor is called or not.
    schoolname = "ABC School";
  }
}

void main() {
  // Here student is object of class Student.
  Student student = Student();
  student.name = "John";
  student.age = 10;
  student.grade = "A";
  print("Name: ${student.name}");
  print("Age: ${student.age}");
  print("School Name: ${student.schoolname}");
  print("Grade: ${student.grade}");
}

Constructor called
Name: John
Age: 10
School Name: ABC School
Grade: A

Challenge

Try to create a class Person with two properties: name, and planet. Create a default constructor to initialize the values of the planet to earth. Create an object of the class Person, set the name to “Your Name” and print the name and planet.

Video

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