Classes

Dart Abstract Classes

Abstract Classes

Dart abstract classes define blueprints with abstract methods.

What is an Abstract Class?

In Dart, an abstract class is a class that cannot be instantiated directly. It serves as a blueprint for other classes, providing a structure that subclasses must implement. Abstract classes are used to define abstract methods, which are methods without implementations. These methods must be implemented by any non-abstract subclass.

Defining an Abstract Class

To define an abstract class in Dart, use the abstract keyword before the class declaration. Abstract classes can contain both abstract methods (without implementations) and concrete methods (with implementations).

Implementing an Abstract Class

When a class inherits from an abstract class, it must implement all of the abstract methods. Here's an example of a subclass implementing the Animal abstract class:

Why Use Abstract Classes?

Abstract classes are useful when you want to define a common interface for a group of classes, while also sharing code among them. They allow you to define methods that must be implemented by subclasses, ensuring consistent behavior across different implementations. Additionally, they can provide default behavior through concrete methods.

Difference Between Abstract Classes and Interfaces

While both abstract classes and interfaces can define methods that must be implemented by subclasses, they serve different purposes. Abstract classes can contain implementation details (concrete methods), while interfaces in Dart (defined using the abstract class without any concrete method) are purely for defining a contract. Use abstract classes when you need to provide some common functionality along with the method declarations.

Key Points to Remember

Abstract classes cannot be instantiated directly.
They can include both abstract methods and concrete methods.
Subclasses must implement all abstract methods.
Abstract classes are ideal for defining blueprints and sharing common code among subclasses.

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