Properties and Methods

In Dart, classes can have properties (also called fields or attributes) and methods (functions that belong to the class). Think of properties as the characteristics of an object, and methods as the actions that object can perform.

Properties

Properties are variables that store data within a class. They define what an object "has" or its state.

class Car {
  // Properties
  String brand;
  String model;
  int year;
  bool isRunning = false;
  
  // Constructor
  Car(this.brand, this.model, this.year);
}

Methods

Methods are functions defined inside a class that can access and modify the object's properties. They define what an object can "do".

class Car {
  String brand;
  String model;
  int year;
  bool isRunning = false;
  
  Car(this.brand, this.model, this.year);
  
  // Methods
  void startEngine() {
    isRunning = true;
    print('$brand $model engine started!');
  }
  
  void stopEngine() {
    isRunning = false;
    print('$brand $model engine stopped.');
  }
  
  String getCarInfo() {
    return '$year $brand $model';
  }
  
  int getAge() {
    return DateTime.now().year - year;
  }
}

Using Properties and Methods

Here's how you can create objects and use their properties and methods:

void main() {
  // Create a car object
  Car myCar = Car('Toyota', 'Camry', 2020);
  
  // Access properties
  print('Brand: ${myCar.brand}');
  print('Model: ${myCar.model}');
  print('Year: ${myCar.year}');
  print('Is running: ${myCar.isRunning}');
  
  // Call methods
  myCar.startEngine();
  print('Car info: ${myCar.getCarInfo()}');
  print('Car age: ${myCar.getAge()} years');
  
  myCar.stopEngine();
}

Property Types

Properties can be of different types and have different access levels:

Property Type	Description	Example
Instance Properties	Belong to a specific instance of the class	String name;
Static Properties	Belong to the class itself, shared by all instances	static int count = 0;
Final Properties	Can only be set once, usually in constructor	final String id;
Private Properties	Start with underscore, only accessible within the same library	String _password;

Method Types

class BankAccount {
  String _accountNumber;
  double _balance = 0.0;
  static int totalAccounts = 0;
  
  BankAccount(this._accountNumber) {
    totalAccounts++;
  }
  
  // Instance method
  void deposit(double amount) {
    _balance += amount;
    print('Deposited \$${amount}. New balance: \$${_balance}');
  }
  
  // Getter method
  double get balance => _balance;
  
  // Setter method
  set accountNumber(String newNumber) {
    _accountNumber = newNumber;
  }
  
  // Static method
  static int getTotalAccounts() {
    return totalAccounts;
  }
  
  // Private method
  void _validateTransaction(double amount) {
    if (amount <= 0) {
      throw Exception('Amount must be positive');
    }
  }
}

Key Points to Remember

• Properties store the state/data of an object
• Methods define the behavior/actions of an object
• Use this keyword when you need to refer to the current instance
• Private members start with an underscore (_)
• Static members belong to the class, not to any specific instance
• Getters and setters provide controlled access to properties

Think of a class like a blueprint for a house. Properties are like the rooms, windows, and doors (what the house has), while methods are like the actions you can perform (opening doors, turning on lights, etc.).