Getters và Setters

🎯 Mục tiêu: Control access với getters/setters.

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💡 Cú pháp

class Rectangle {
  double width, height;

  Rectangle(this.width, this.height);

  // Getter
  double get area => width * height;

  // Setter
  set area(double value) {
    width = sqrt(value);
    height = sqrt(value);
  }
}

var rect = Rectangle(10, 20);
print(rect.area);  // 200.0
rect.area = 100;   // width = height = 10

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📝 Private + Getter/Setter

class User {
  int _age = 0;

  int get age => _age;

  set age(int value) {
    if (value >= 0 && value <= 150) {
      _age = value;
    }
  }
}

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📱 Trong Flutter

class CounterState {
  int _count = 0;

  int get count => _count;

  void increment() => _count++;
  void decrement() => _count--;
}

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✅ Checklist

• get cho computed properties
• set cho validation
• _ prefix cho private

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