dart code sample

sample.dart

import 'dart:math' as Math;

class Circulo {
  int ri;
	
  Circulo(int r){
    this.ri = r;
  }  
  
  calcularArea(int r){
    return Math.PI * Math.pow(r, 2);
  }
}

class CoroaCircular extends Circulo{
  int re;
  
  CoroaCircular(int r, int re): super(r) {
    this.re = re;
  }
  
  calculaAreaDaCoroa(){
    return this.calcularArea(this.re) - this.calcularArea(this.ri);
  }
}

void main() {
	var x1 = 10;
  var x2 = 20;
  var cc = new CoroaCircular(x1, x2);
  print("area = " + cc.calculaAreaDaCoroa().toString());
}