Classes

• Dart is an object-oriented language with classes and mixin-based inheritance.
• Every object is an instance of a class, and all classes descend from Object.
• Mixin-based inheritance means that although every class (except for Object) has exactly one superclass, a class body can be reused in multiple class hierarchies.

Use a dot (.) to refer to an instance variable or method.

var p = Point(2, 2); 

// Set the value of the instance variable y.
p.y = 3; 

// Get the value of y. 
assert(p.y == 3); 

// Invoke distanceTo() on p. 
num distance = p.distanceTo(Point(4, 4));

Use ?. instead of . to avoid an exception when the leftmost operand is null.

// If p is non-null, set its y value to 4. 
p?.y = 4;

To get an object’s type at runtime, you can use Object’s runtimeType property, which returns a Type object.

print('The type of a is ${a.runtimeType}');

class Television { 
   void turnOn() { 
      _illuminateDisplay(); 
      _activateIrSensor(); 
   } 
   // ··· 
} 

class SmartTelevision extends Television { 
   void turnOn() { 
      super.turnOn(); 
      _bootNetworkInterface(); 
      _initializeMemory(); 
      _upgradeApps(); 
   } 
   // ··· 
}

Use extends to create a subclass, and super to refer to the superclass.

class SmartTelevision extends Television { 
   @override void turnOn() {...} 
   // ··· 
}

Subclasses can override instance methods, getters, and setters.