Outline of The Article

1. Introduction — Overview of class extension in Dart.
2. Understanding Class Extension — Explanation of the purpose behind class extension, including a basic example.
3. Using the extends Keyword — How to create a subclass and the inheritance of properties and methods.
4. The super Keyword — Usage of super for referencing superclass methods and properties with illustrative code.
5. Overriding Members — Discussion on how subclasses can override methods, getters, and setters.
6. Handling Non-existent Methods — Introduction to the noSuchMethod() method and its role in managing calls to non-existent members.
7. Conclusion — Recap of key insights from the guide.
8. FAQs — Addressing common inquiries related to class extension topics.

What Does Extending a Class Mean?

Imagine you possess a blueprint for constructing a house that outlines essential features like walls, a roof, and doors. If you wish to design a specific type of house, such as a bungalow, this new blueprint would inherit the fundamental features from the general house design while incorporating unique traits, like a single-story layout.

Similarly, extending a class in Dart begins with an existing class, termed the superclass, which establishes a set of properties and methods. You then create a new class, known as the subclass, which inherits all properties and methods from the superclass and can also introduce its unique attributes and behaviors.

Benefits of Class Extension

Extending classes enhances code reusability and maintainability. By inheriting properties and methods from a superclass, you can avoid code duplication and concentrate on developing the specific functionalities of the subclass. This approach leads to a more organized and comprehensible codebase.

Understanding Class Extension

In Dart, class extension allows for the creation of a subclass that inherits characteristics and behaviors from an existing class, referred to as the superclass. The extends keyword is crucial for establishing a subclass, while the super keyword is used to refer back to the superclass.

For instance:

class Television {

void turnOn() {

_illuminateDisplay();

_activateIrSensor();

}

// Additional methods and properties...

}

class SmartTelevision extends Television {

void turnOn() {

super.turnOn(); // Calls the turnOn method of the superclass

_bootNetworkInterface();

_initializeMemory();

_upgradeApps();

}

// More methods and properties for SmartTelevision...

}

In this example, SmartTelevision inherits the turnOn method from Television and adds its own functionalities.

Overriding Members

Subclasses in Dart have the capability to override instance methods, getters, and setters. The @override annotation is employed to signify intentional overriding. It is crucial that the method's return type and parameter types align with those of the method being overridden.

For example:

class Television {

// Existing methods and properties...

set contrast(int value) {...}

}

class SmartTelevision extends Television {

@override

set contrast(num value) {...} // Overriding the contrast setter

// Additional methods and properties for SmartTelevision...

}

In this case, the SmartTelevision class overrides the contrast setter from the Television class, altering the parameter type from int to num.

Handling Non-existent Methods

Dart allows for the detection of attempts to call non-existent methods or instance variables through the noSuchMethod() method.

Consider the following:

class A {

@override

void noSuchMethod(Invocation invocation) {

print('Attempted to use a non-existent member: ${invocation.memberName}');

}

}

In this instance, if an undefined method or variable is invoked on an instance of class A, the noSuchMethod() method will be triggered.