Inheritance

Inheritance in Dart Programming

Inheritance is one of the core concepts of Object-Oriented Programming (OOP). It allows a class to inherit properties and methods from another class. In Dart, the extends keyword is used to implement inheritance, enabling you to create a new class based on an existing class.

Here's an overview of inheritance in Dart:

1. Base Class (Parent Class): This is the class whose properties and methods are inherited.

2. Derived Class (Child Class): This is the class that inherits properties and methods from the base class.

Key Points:

• A child class can access all non-private members of the parent class.

• The child class can override methods in the parent class to provide specific functionality.

• Constructors are not inherited by default, but a child class can call the parent class constructor using super().

Basic Example of Inheritance

1. Simple Inheritance Example

class Animal {

 String name;

 Animal(this.name);

 void speak() {

   print("$name makes a sound.");

 }

}

class Dog extends Animal {

 Dog(String name) : super(name);

 @override

 void speak() {

   print("$name barks.");

 }

}

void main() {

 var dog = Dog("Buddy");

 dog.speak();  // Output: Buddy barks.

}

In this example:

• Animal is the base class with a name property and a speak() method.

• Dog is the derived class that extends Animal and overrides the speak() method.

2. Constructor Inheritance and Initialization

class Person {

 String name;

 int age;

 // Constructor of the base class

 Person(this.name, this.age);

 void introduce() {

   print("Hello, I am $name and I am $age years old.");

 }

}

class Student extends Person {

 String school;

 // Constructor of the derived class

 Student(String name, int age, this.school) : super(name, age);

 @override

 void introduce() {

   super.introduce();

   print("I study at $school.");

 }

}

void main() {

 var student = Student("Alice", 20, "XYZ University");

 student.introduce();

 // Output:

 // Hello, I am Alice and I am 20 years old.

 // I study at XYZ University.

}

In this example:

• The Student class uses super() to call the constructor of the base class Person.

• The introduce() method is overridden in the Student class to add additional functionality.

3. Method Overriding

class Vehicle {

 void start() {

   print("Vehicle is starting.");

 }

}

class Car extends Vehicle {

 @override

 void start() {

   print("Car is starting with keyless entry.");

 }

}

void main() {

 var car = Car();

 car.start();  // Output: Car is starting with keyless entry.

}

In this example:

• The Car class overrides the start() method of the Vehicle class to provide its own implementation.

• The @override annotation ensures that the method is correctly overridden.

4. Inheritance with Multiple Levels

class Shape {

 void draw() {

   print("Drawing a shape.");

 }

}

class Circle extends Shape {

 @override

 void draw() {

   print("Drawing a circle.");

 }

}

class ColoredCircle extends Circle {

 String color;

 ColoredCircle(String color) : color = color;

 @override

 void draw() {

   super.draw();

   print("The color is $color.");

 }

}

void main() {

 var coloredCircle = ColoredCircle("Red");

 coloredCircle.draw();

 // Output:

 // Drawing a circle.

 // The color is Red.

}

In this example:

• ColoredCircle extends Circle, which in turn extends Shape, creating a multilevel inheritance structure.

• ColoredCircle overrides the draw() method, calling the draw() method from Circle using super.draw().

5. Using super() for Accessing Parent Class Members

class Animal {

 String name;

 Animal(this.name);

 void speak() {

   print("$name makes a sound.");

 }

}

class Dog extends Animal {

 Dog(String name) : super(name);

 void speak() {

   super.speak();  // Calls Animal's speak method

   print("$name barks.");

 }

}

void main() {

 var dog = Dog("Buddy");

 dog.speak();

 // Output:

 // Buddy makes a sound.

 // Buddy barks.

}

In this example:

• super.speak() is used to call the speak() method of the parent class Animal before adding additional functionality in the Dog class.

6. Inheritance with Private Members

class Animal {

 String name;

 int _age; // Private member

 Animal(this.name, this._age);

 void showDetails() {

   print("Name: $name, Age: $_age");

 }

}

class Dog extends Animal {

 Dog(String name, int age) : super(name, age);

 void showDogDetails() {

   // print("Age: $_age"); // Error: _age is private in Animal class

   print("Dog's Name: $name");

 }

}

void main() {

 var dog = Dog("Buddy", 3);

 dog.showDetails();  // Output: Name: Buddy, Age: 3

 dog.showDogDetails();  // Output: Dog's Name: Buddy

}

In this example:

• The Animal class has a private member _age, which is not directly accessible by the Dog class.

• The Dog class can still access the public name but cannot directly access _age.

7. Inheritance with super in a Constructor

class Animal {

 String name;

 Animal(this.name);

 void display() {

   print("Animal Name: $name");

 }

}

class Dog extends Animal {

 int age;

 Dog(String name, this.age) : super(name);

 @override

 void display() {

   super.display();

   print("Dog Age: $age");

 }

}

void main() {

 var dog = Dog("Max", 5);

 dog.display();

 // Output:

 // Animal Name: Max

 // Dog Age: 5

}

In this example:

• The Dog class extends Animal and calls the Animal constructor using super(name).

• The display() method is overridden in the Dog class to display additional information.

Summary of Inheritance Concepts in Dart

1. Base and Derived Classes: A derived class inherits properties and methods from the base class.

2. Method Overriding: Derived classes can override methods from the base class to provide specialized behavior.

3. Constructor Inheritance: A derived class can call a constructor of the base class using super().

4. Access to Parent Class Members: Derived classes can access non-private members of the base class, but private members are not directly accessible.

5. Super Keyword: super is used to refer to the parent class, both for calling methods and constructors.

Single Inheritance

In single inheritance, a subclass inherits from only one superclass.

1. Single Inheritance with Animal and Dog

class Animal {

 void sound() {

   print("Animal makes a sound");

 }

}

class Dog extends Animal {

 void bark() {

   print("Dog barks");

 }

}

void main() {

 Dog dog = Dog();

 dog.sound();

 dog.bark();

}

2. Single Inheritance with Vehicle and Car

class Vehicle {

 void start() {

   print("Vehicle started");

 }

}

class Car extends Vehicle {

 void drive() {

   print("Car is driving");

 }

}

void main() {

 Car car = Car();

 car.start();

 car.drive();

}

3. Single Inheritance with Shape and Circle

class Shape {

 void draw() {

   print("Drawing shape");

 }

}

class Circle extends Shape {

 void drawCircle() {

   print("Drawing circle");

 }

}

void main() {

 Circle circle = Circle();

 circle.draw();

 circle.drawCircle();

}

4. Single Inheritance with Person and Student

class Person {

 void introduce() {

   print("I am a person");

 }

}

class Student extends Person {

 void study() {

   print("I am studying");

 }

}

void main() {

 Student student = Student();

 student.introduce();

 student.study();

}

Multilevel Inheritance

In multilevel inheritance, a class is derived from a class which is also derived from another class.

5. Multilevel Inheritance with Animal, Mammal, and Dog

class Animal {

 void sound() {

   print("Animal makes a sound");

 }

}

class Mammal extends Animal {

 void breathe() {

   print("Mammal breathes");

 }

}

class Dog extends Mammal {

 void bark() {

   print("Dog barks");

 }

}

void main() {

 Dog dog = Dog();

 dog.sound();

 dog.breathe();

 dog.bark();

}

6. Multilevel Inheritance with Employee, Manager, and Director

class Employee {

 void work() {

   print("Employee is working");

 }

}

class Manager extends Employee {

 void manage() {

   print("Manager is managing");

 }

}

class Director extends Manager {

 void makeDecisions() {

   print("Director makes decisions");

 }

}

void main() {

 Director director = Director();

 director.work();

 director.manage();

 director.makeDecisions();

}

7. Multilevel Inheritance with Machine, Vehicle, and Car

class Machine {

 void operate() {

   print("Machine is operating");

 }

}

class Vehicle extends Machine {

 void start() {

   print("Vehicle started");

 }

}

class Car extends Vehicle {

 void drive() {

   print("Car is driving");

 }

}

void main() {

 Car car = Car();

 car.operate();

 car.start();

 car.drive();

}

8. Multilevel Inheritance with LivingBeing, Plant, and Flower

class LivingBeing {

 void live() {

   print("Living being lives");

 }

}

class Plant extends LivingBeing {

 void grow() {

   print("Plant grows");

 }

}

class Flower extends Plant {

 void bloom() {

   print("Flower blooms");

 }

}

void main() {

 Flower flower = Flower();

 flower.live();

 flower.grow();

 flower.bloom();

}

Hierarchical Inheritance

In hierarchical inheritance, multiple subclasses inherit from a single superclass.

9. Hierarchical Inheritance with Animal, Dog, and Cat

class Animal {

 void sound() {

   print("Animal makes a sound");

 }

}

class Dog extends Animal {

 void bark() {

   print("Dog barks");

 }

}

class Cat extends Animal {

 void meow() {

   print("Cat meows");

 }

}

void main() {

 Dog dog = Dog();

 Cat cat = Cat();

 dog.sound();

 dog.bark();

 cat.sound();

 cat.meow();

}

10. Hierarchical Inheritance with Shape, Circle, and Rectangle

class Shape {

 void draw() {

   print("Drawing shape");

 }

}

class Circle extends Shape {

 void drawCircle() {

   print("Drawing circle");

 }

}

class Rectangle extends Shape {

 void drawRectangle() {

   print("Drawing rectangle");

 }

}

void main() {

 Circle circle = Circle();

 Rectangle rectangle = Rectangle();

 circle.draw();

 circle.drawCircle();

 rectangle.draw();

 rectangle.drawRectangle();

}

11. Hierarchical Inheritance with Vehicle, Car, and Bike

class Vehicle {

 void start() {

   print("Vehicle started");

 }

}

class Car extends Vehicle {

 void drive() {

   print("Car is driving");

 }

}

class Bike extends Vehicle {

 void ride() {

   print("Bike is riding");

 }

}

void main() {

 Car car = Car();

 Bike bike = Bike();

 car.start();

 car.drive();

 bike.start();

 bike.ride();

}

12. Hierarchical Inheritance with Employee, Developer, and Tester

class Employee {

 void work() {

   print("Employee is working");

 }

}

class Developer extends Employee {

 void develop() {

   print("Developer is coding");

 }

}

class Tester extends Employee {

 void test() {

   print("Tester is testing");

 }

}

void main() {

 Developer developer = Developer();

 Tester tester = Tester();

 developer.work();

 developer.develop();

 tester.work();

 tester.test();

}

Using Mixins for Multiple Inheritance Behavior

Dart doesn't support multiple inheritance, but mixins allow you to add multiple behaviors to a class.

13. Mixin Example with Swimmer and Flyer

mixin Swimmer {

 void swim() {

   print("Swimming");

 }

}

mixin Flyer {

 void fly() {

   print("Flying");

 }

}

class Duck with Swimmer, Flyer {}

void main() {

 Duck duck = Duck();

 duck.swim();

 duck.fly();

}

14. Mixin Example with Eater and Sleeper

mixin Eater {

 void eat() {

   print("Eating");

 }

}

mixin Sleeper {

 void sleep() {

   print("Sleeping");

 }

}

class Human with Eater, Sleeper {}

void main() {

 Human human = Human();

 human.eat();

 human.sleep();

}

15. Mixin Example with Walker and Runner

mixin Walker {

 void walk() {

   print("Walking");

 }

}

mixin Runner {

 void run() {

   print("Running");

 }

}

class Athlete with Walker, Runner {}

void main() {

 Athlete athlete = Athlete();

 athlete.walk();

 athlete.run();

}

16. Mixin Example with Reader and Writer

mixin Reader {

 void read() {

   print("Reading");

 }

}

mixin Writer {

 void write() {

   print("Writing");

 }

}

class Author with Reader, Writer {}

void main() {

 Author author = Author();

 author.read();

 author.write();

}

17. Mixin Example with Painter and Sculptor

mixin Painter {

 void paint() {

   print("Painting");

 }

}

mixin Sculptor {

 void sculpt() {

   print("Sculpting");

 }

}

class Artist with Painter, Sculptor {}

void main() {

 Artist artist = Artist();

 artist.paint();

 artist.sculpt();

}

18. Mixin Example with Teacher and Researcher

mixin Teacher {

 void teach() {

   print("Teaching");

 }

}

mixin Researcher {

 void research() {

   print("Researching");

 }

}

class Professor with Teacher, Researcher {}

void main() {

 Professor professor = Professor();

 professor.teach();

 professor.research();

}

19. Mixin Example with Gamer and Coder

mixin Gamer {

 void play() {

   print("Playing games");

 }

}

mixin Coder {

 void code() {

   print("Coding");

 }

}

class GameDeveloper with Gamer, Coder {}

void main() {

 GameDeveloper dev = GameDeveloper();

 dev.play();

 dev.code();

}

20. Mixin Example with Singer and Dancer

mixin Singer {

 void sing() {

   print("Singing");

 }

}

mixin Dancer {

 void dance() {

   print("Dancing");

 }

}

class Performer with Singer, Dancer {}

void main() {

 Performer performer = Performer();

 performer.sing();

 performer.dance();

}