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What is the difference between a named constructor and a default constructor in Dart?

Parthiban Kannan
Updated on December 6, 2025

1 min read

In Dart, the difference between a default constructor and a named constructor lies in how they are defined and used to create objects.

A default constructor is the primary constructor of a class and doesn’t have a name other than the class name itself. It’s used for the most common way of creating an object and can be parameterized to initialize instance variables. For example:

📄
filename.dart 
class User {
  String name;
  int age;

  // Default constructor
  User(this.name, this.age);
}

var user1 = User('Aswini', 25);

Here, User('Aswini', 25) calls the default constructor to initialize the object.

A named constructor, on the other hand, allows you to create additional constructors with custom names for special cases or alternative ways to initialize an object. Named constructors are defined using ClassName.constructorName(). For example:

📄
filename.dart 
class User {
  String name;
  int age;

  User(this.name, this.age); // default constructor

  // Named constructor
  User.guest() {
    name = 'Guest';
    age = 0;
  }
}

var guestUser = User.guest();

Named constructors are especially useful when you want to create objects with default, placeholder, or special configurations without overloading the default constructor.

I’ve applied this in Flutter projects when working with API data. For example, I used the default constructor to initialize a Product object with API data and a named constructor to create a placeholder product while waiting for the API response.

A challenge is remembering when to use named constructors versus factory constructors, especially for immutable objects. The limitation of named constructors is that they still create new objects every time; for shared instances, a factory constructor is often a better alternative.

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