Class và Object trong Dart

class Person {
  String name = '';
  int age = 0;
  
  void introduce() {
    print('Tôi là $name, $age tuổi');
  }
}
 
void main() {
  var person = Person();
  person.name = 'Alice';
  person.age = 25;
  person.introduce();
}

class Person {
  String name;
  int age;
  
  // Constructor
  Person(this.name, this.age);
  
  void introduce() {
    print('Tôi là $name, $age tuổi');
  }
}
 
void main() {
  var person = Person('Bob', 30);
  person.introduce();
}

class Point {
  double x, y;
  
  Point(this.x, this.y);
  
  // Named constructor
  Point.origin() : x = 0, y = 0;
  
  Point.fromJson(Map<String, double> json)
      : x = json['x']!,
        y = json['y']!;
}
 
void main() {
  var p1 = Point(3, 4);
  var p2 = Point.origin();
  var p3 = Point.fromJson({'x': 1.0, 'y': 2.0});
}

class BankAccount {
  String _accountNumber;  // Private
  double _balance = 0;    // Private
  
  BankAccount(this._accountNumber);
  
  double get balance => _balance;
  
  void deposit(double amount) {
    _balance += amount;
  }
}

class Rectangle {
  double width, height;
  
  Rectangle(this.width, this.height);
  
  // Getter
  double get area => width * height;
  
  // Setter
  set dimension(double value) {
    width = value;
    height = value;
  }
}
 
void main() {
  var rect = Rectangle(5, 3);
  print(rect.area);     // 15
  rect.dimension = 4;   // Sets both
}

class Math {
  static const double pi = 3.14159;
  
  static int max(int a, int b) => a > b ? a : b;
}
 
void main() {
  print(Math.pi);         // 3.14159
  print(Math.max(5, 3));  // 5
}

class Person {
  final String id;       // Phải gán trong constructor
  final String name;
  
  static const String species = 'Human';
  
  Person(this.id, this.name);
}

class Person {
  String name = '';
  int age = 0;
  String city = '';
}
 
void main() {
  var person = Person()
    ..name = 'Alice'
    ..age = 25
    ..city = 'Hanoi';
}