Step 1 - Class and object

class Point {
  double x;
  double y;

  Point(this.x, this.y);
}

void main() {
  Point a = Point(1, 2);
  Point b = Point(4, 6);
  print('${a.x}, ${a.y}');
  print('${b.x}, ${b.y}');
}

• A class is a blueprint; Point(1, 2) is an object (instance).
• Fields x and y hold state for each instance.

Step 2 - Named constructor

class User {
  String name;
  int age;

  User(this.name, this.age);

  User.guest()
      : name = 'Guest',
        age = 0;
}

void main() {
  User u1 = User('Asha', 20);
  User u2 = User.guest();
  print('${u1.name} ${u1.age}');
  print('${u2.name} ${u2.age}');
}

• Extra constructors give clear ways to create valid objects.

Step 3 - this in methods

class Counter {
  int value = 0;

  void increment() {
    value = value + 1;
  }

  void add(int n) {
    this.value = this.value + n;
  }
}

void main() {
  Counter c = Counter();
  c.increment();
  c.add(5);
  print(c.value);
}

• Inside instance methods, this means the current object. You can omit this when there is no name clash.

Good habit

• Keep constructors simple; push behavior into methods.
• Name classes with PascalCase, instances with camelCase.

Practice tasks

• Add a Rectangle with width, height, and a method double area().
• Add a reset() method on Counter that sets value to 0.
• Create two instances of the same class and show their fields differ.