program to create interface
the class that implements an interface must have implementation for all methods in the interface

// creating an interface using concrete class
class Laptop {
    // method
  turnOn() {
    print('Laptop turned on');
  }
    // method
  turnOff() {
    print('Laptop turned off');
  }
}

class MacBook implements Laptop {
  // implementation of turnOn()
  @override
  turnOn() {
    print('MacBook turned on');
  }

  // implementation of turnOff()
  @override
  turnOff() {
    print('MacBook turned off');
  }
}

void main() {
  var macBook = MacBook();
  macBook.turnOn();
  macBook.turnOff();
}

________________________________________________________________________________________________________

abstract class as interface

// abstract class as interface
abstract class Vehicle {
  void start();
  void stop();
}
// implements interface
class Car implements Vehicle {
  @override
  void start() {
    print('Car started');
  }

  @override
  void stop() {
    print('Car stopped');
  }
}

void main() {
  var car = Car();
  car.start();
  car.stop();
}

________________________________________________________________________________________________________

example of Implementation of multiple interfaces

// abstract class as interface
abstract class Area {
  void area();
}
// abstract class as interface
abstract class Perimeter {
  void perimeter();
}
// implements multiple interfaces
class Rectangle implements Area, Perimeter {
    // properties
  int length, breadth;

 // constructor
  Rectangle(this.length, this.breadth);

// implementation of area()
  @override
  void area() {
    print('The area of the rectangle is ${length * breadth}');
  }
// implementation of perimeter()
  @override
  void perimeter() {
    print('The perimeter of the rectangle is ${2 * (length + breadth)}');
  }
}

void main() {
  Rectangle rectangle = Rectangle(10, 20);
  rectangle.area();
  rectangle.perimeter();
}

________________________________________________________________________________________________________

abstract class as interface

// abstract class as interface
abstract class Person {
    // properties
  String? name;
  // abstract method
  void run();
  void walk();
}

class Student implements Person {
    // properties
  String? name;
 
 // implementation of run()
 @override
  void run() {
    print('Student is running');
  }
  // implementation of walk()
  @override
  void walk() {
    print('Student is walking');
  }
}

void main() {
  var student = Student();
  student.name = 'John';
  print(student.name);
  student.run();
  student.walk();
}

________________________________________________________________________________________________________

another example of abstract class as interface

// abstract class as interface
abstract class CalculateTotal {
  int total();
}
// abstract class as interface
abstract class CalculateAverage {
  double average();
}
// implements multiple interfaces
class Student implements CalculateTotal, CalculateAverage {
// properties
  int marks1, marks2, marks3;
// constructor
  Student(this.marks1, this.marks2, this.marks3);
// implementation of average()
  @override
  double average() {
    return total() / 3;
  }
// implementation of total()
  @override
  int total() {
    return marks1 + marks2 + marks3;
  }
}

void main() {
  Student student = Student(90, 80, 70);
  print('Total marks: ${student.total()}');
  print('Average marks: ${student.average()}');
}

________________________________________________________________________________________________________