Classes and Objects in Dart

What are Classes and Objects?

A class is a blueprint that defines the properties (fields) and behaviors (methods) of a type. An object is a specific instance of a class — it holds actual data following the blueprint.

Defining a Class

class Person {
  // Fields (properties)
  String name;
  int age;
  String email;

  // Constructor
  Person(this.name, this.age, this.email);

  // Methods (behaviors)
  void introduce() {
    print('Hi, I am $name, $age years old.');
  }

  bool isAdult() => age >= 18;

  @override
  String toString() => 'Person($name, age=$age)';
}

Creating Objects

void main() {
  // Create objects (instances of Person)
  Person alice = Person('Alice', 28, 'alice@email.com');
  Person bob   = Person('Bob', 17, 'bob@email.com');

  // Or use var / final
  var carol = Person('Carol', 32, 'carol@email.com');
}

Accessing Members

void main() {
  var p = Person('Alice', 28, 'alice@email.com');

  // Access fields
  print(p.name);    // Alice
  print(p.age);     // 28

  // Call methods
  p.introduce();    // Hi, I am Alice, 28 years old.
  print(p.isAdult()); // true

  // Modify fields
  p.age = 29;
  print(p);         // Person(Alice, age=29)
}

Full Example

class BankAccount {
  String owner;
  double balance;

  BankAccount(this.owner, this.balance);

  void deposit(double amount) {
    balance += amount;
    print('Deposited \$$${amount.toStringAsFixed(2)}. Balance: \$$${balance.toStringAsFixed(2)}');
  }

  void withdraw(double amount) {
    if (amount > balance) {
      print('Insufficient funds!');
      return;
    }
    balance -= amount;
    print('Withdrew \$$${amount.toStringAsFixed(2)}. Balance: \$$${balance.toStringAsFixed(2)}');
  }
}

void main() {
  var account = BankAccount('Alice', 1000.0);
  account.deposit(500.0);
  account.withdraw(200.0);
  account.withdraw(2000.0);
}

Deposited $500.00. Balance: $1500.00
Withdrew $200.00. Balance: $1300.00
Insufficient funds!

🧠 Quiz

Summary

A class defines the structure (fields) and behavior (methods) of a type. Objects are instances of a class. Create objects with ClassName(args). Access fields and methods with the dot operator. Each object has its own copy of the field values.