Inheritance (Abstract Class & Getters/Setters) - 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();
  
  Circle circle1 = Circle(radius: 66);
  circle1.showPerimeter();
  print(circle1.diameter);
  circle1.showDiameter();
  
  circle1.diameter = 220;
  circle1.showDiameter();
  circle1.showPerimeter();
  
  //Shape shape = new Shape(1, 2);
}


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

class Rectangle extends Shape {
  Rectangle(int length,  int breadth) : super(length, breadth);
  void showPerimeter() {
    print("The perimeter of rectangle with length $length and breadth $breadth is ${perimeter()}");
  }
}

class Square extends Shape{
  Square(int size) : super(size, size);
  void showPerimeter() {
    print("The perimeter of square with size $length is ${perimeter()}");
  }
}

class Circle extends Shape{
  Circle({@required int radius}) : super(radius, radius);
  @override int perimeter() {
    return (2 * length * 3.14).toInt();
  }
  int get diameter {
    return length * 2;
  }
  
  set diameter(int d){
    length = d ~/ 2;
  }
  
  void showDiameter() {
    print("the diameter of the circle is $diameter");
  }
  void showPerimeter() {
    print("The perimeter of circle with radius $length is ${perimeter()}");
  }
}

abstract class Shape {
  int length;
  int breadth;
  Shape(this.length, this.breadth);
  
  int perimeter() {
    return 2 * (length + breadth);
  }
  
  void showPerimeter();
  
  //add area
}

//add 3DShape