Dart: Classes & Constructors

What you will learn

Dart's concise class syntax with constructor parameter shorthand, named constructors, and factory constructors.

Defining a class

class Person {
  String name;
  int age;

  // Constructor with shorthand parameter assignment
  Person(this.name, this.age);

  void sayHello() {
    print("Hi, I'm $name");
  }
}

var alice = Person('Alice', 25);
alice.sayHello();

this.name in the constructor parameter list automatically assigns the parameter to the field — no boilerplate.

Named constructors

Classes can have multiple constructors with different names:

class User {
  final String name;
  final String role;

  User(this.name, this.role);
  User.admin(String name) : this(name, 'admin');
  User.guest() : name = 'Guest', role = 'guest';
}

var admin = User.admin('Alice');
var guest = User.guest();

Getters and setters

class Rectangle {
  double width, height;

  Rectangle(this.width, this.height);

  double get area => width * height;  // computed property
  set scale(double factor) {          // setter
    width *= factor;
    height *= factor;
  }
}

var r = Rectangle(10, 5);
print(r.area);   // 50
r.scale = 2;
print(r.area);   // 200

Static members

class MathUtils {
  static double pi = 3.14159;
  static int add(int a, int b) => a + b;
}

print(MathUtils.pi);   // 3.14159
print(MathUtils.add(2, 3));  // 5

Common mistakes

• Forgetting that Dart fields must be initialized (in constructor initializer, declaration, or constructor body)
• Using new keyword — it's optional in Dart 2+, prefer omitting it
• Thinking final fields can be set after the constructor runs — they must be set in the constructor initializer list
• Forgetting to use this.property when constructor parameter shadows field name (the shorthand this.x handles this)

Quick check below!