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Learn Dart: The First Step to Flutter

Advanced Class Mechanics

Explore advanced class mechanics in Dart to improve your object-oriented programming skills. Understand how to customize string output, use static members, implement factory constructors, enforce contracts with implicit interfaces, and share code via mixins. This lesson prepares you to write flexible, reusable, and maintainable Dart classes for real-world applications.

We'll cover the following...

Customizing string representations

When we print an object in Dart, the default output is often unhelpful, displaying something like Instance of 'Person'. This happens because our class inherits a basic toString() method from the root Object class.

To provide a readable description of our object, we can override the toString() method and define a custom text format.

Dart
class Person {
  String name;
  int age;
  Person(this.name, this.age);
  @override
  String toString() {
    return 'Person(name: $name, age: $age)';
  }
}
void main() {
  final person = Person('Sarah', 25);
  print(person); 
}

  • Line 7: We apply the @override annotation to modify the inherited string behavior.

  • Lines 8—10: We return a formatted string that includes the actual state of our instance variables.

  • Line 15: We pass the object directly to the print function. Dart automatically calls our overridden method, outputting our custom string instead of the generic default.

Static members

Properties and methods normally belong to individual ...