Inheritance 1 - Object Oriented programming

main.dart

import "package:flutter/material.dart";

void main() {
  //new instance of class
  MyNewClass myNewClass = new MyNewClass();
  var anotherInstance = new MyNewClass();
  print(myNewClass.runtimeType);
  anotherInstance.sayHello();
  
  Shape rectangle1 = new Rectangle(20, 30);
  print(rectangle1.runtimeType);
  print(rectangle1.perimeter());
  rectangle1.showPerimeter();
  
  Shape square1 = new Square(35);
  print(square1.runtimeType);
  print(square1.perimeter());
  square1.showPerimeter();
  
  Rectangle(20, 20).showPerimeter();
  Square(20).showPerimeter();
  
  Shape circle1 = Circle(radius: 66);
  circle1.showPerimeter();
  
  Shape circle = Circle.fromDiameter(56);
  circle.showPerimeter();
}


class MyNewClass {
  void sayHello() {
    print("hello");
  }
}

class Rectangle extends Shape {
  Rectangle(int length,  int breadth) : super(length, breadth);
}

class Square extends Shape{
  Square(int size) : super(size, size);
}

class Circle extends Shape{
  Circle({@required int radius}) : super(radius, radius);
  Circle.fromDiameter(int diameter) : assert(diameter%2==0, "Must be divisible by 2"), super(diameter~/2, diameter~/2);
  @override int perimeter() {
    return (2 * length * 3.14).toInt();
  }
}

class Shape {
  int length;
  int breadth;
  Shape(this.length, this.breadth);
  
  int perimeter() {
    return 2 * (length + breadth);
  }
  
  void showPerimeter() {
    print("Perimeter is ${perimeter()}");
  }
}