Abstract Classes

Abstract Classes

About

• Abstract classes define incomplete blueprints.
• Cannot be instantiated directly.
• Enforce implementation contracts.
• Support partial implementations.

Main Topics

1. Basic Abstract Class

   • Definition: Class with abstract modifier.
   • Example:

     abstract class Shape {
       double area(); // Abstract method
     }

2. Concrete Subclasses

   • Definition: Implementing abstract members.
   • Example:

     class Circle extends Shape {
       @override
       double area() => pi * radius * radius;
     }

3. Partial Implementations

   • Definition: Mixing concrete and abstract.
   • Example:

     abstract class Animal {
       void eat(); // Abstract
       void sleep() => print('Sleeping'); // Concrete
     }

4. Interface Enforcement

   • Definition: Required method signatures.
   • Example:

     abstract class Repository {
       Future<Data> fetch();
     }

How to Use

• Declare: Use abstract modifier
• Implement: Subclasses must override abstracts
• Extend: Can include concrete methods
• Combine: With interfaces and mixins

How It Works

• Instantiation: Only through subclasses
• Type System: Abstract types as references
• Contracts: Compile-time enforcement

Example Session:

void main() {
  Shape circle = Circle(radius: 5); // Abstract type reference
  print(circle.area());
}

Conclusion

Abstract classes strike a balance between interfaces and full implementations, serving as powerful tools for defining shared contracts while allowing flexible concrete implementations in Dart applications.