Constructor

Learn to define the class constructor.

Constructor

The constructor is a special method called when an instance is created. It shares the class name. Example: class User { String name; User(this.name); }.

Here User(this.name) is the short form; it means 'assign the parameter to the same-named field'. The long form: User(String name) { this.name = name; }.

The constructor prepares the object: it sets field values, allocates resources. Calling User('Ayşe') returns a User instance with name set to 'Ayşe'. This lesson focuses on the this.name shorthand; the this keyword is covered in a separate lesson.

Short and long form

The short form is very common in Dart constructors: User(this.name). It means 'assign the parameter to the same-named field'. The field name is filled automatically.

The long form is more explicit: User(String name) { this.name = name; }. Here you assign the parameter name to the field with this.name. this means 'this instance'.

Both do the same thing. The short form is the idiomatic Dart style; it is preferred in practice. The long form helps when you need extra logic.

Exercise User constructor

Define a User class with a String name field and a User(this.name) constructor. Inside main create an instance with User('Ayşe') and print it with print(u.name).

Show example solution

class User {
  String name;
  User(this.name);
}

void main() {
  var u = User('Ayşe');
  print(u.name);
}

Test yourself

Match the constructor parts

User

Constructor name
this.name

Shorthand assign
User('Ayşe')

Instance creation
name

Property name
What does User(this.name) do?
- Throws an error
- Ignores the name parameter
- Deletes the class
- Assigns the name parameter to the name field
Show answer

Assigns the name parameter to the name field — this.name is the shorthand assignment.

Constructor short form

class User {
  String name;
  User(____);
}

Show answer

class User {
  String name;
  User(this.name);
}

Next lesson: Instance variables

We Are Enhancing Your Experience

Cookie Preferences

Strictly Necessary Cookies

Analytical Cookies