app.dart

main() {
  Map json = jsonDecode('{"id": 1, "price": 100, "type": "fruits", "color": "red"}');
  ProductFactory productFactory = ProductFactory.fromJson(json);

}

class ProductFactory {

  CurrentProduct currentProduct;

  ProductFactory.fromJson(Map json)
  {
    if (json['type'] == 'bottles')
    {
      currentProduct = Bottles(json);
    }
    if (json['type'] == 'fruits')
    {
      currentProduct = Apples(json);
    }

  }

}

abstract class CurrentProduct
{
  int id;
  num price;

  CurrentProduct(Map json)
  {
    this.id = json['id'];
    this.price = json['price'];
  }


}

class Bottles extends CurrentProduct {
  String content;
  Bottles(Map json): super(json)
  {
    this.content = json['content'];
  }

}

class Apples extends CurrentProduct {
  String color;
  Apples(Map json): super(json)
  {
    this.color = json['color'];
  }
}