Extended Builder Pattern

abstract class Pizza {
    public enum Topping {HAM, MUSHROOM, ONION, PEPPER, SAUSAGE}

    final Set<Topping> toppings;

    abstract static class Builder<V extends Pizza.Builder<V>> {
        EnumSet<Topping> toppings = EnumSet.noneOf(Topping.class);

        public V addTopping(Topping topping) {
            toppings.add(Objects.requireNonNull(topping));
            return self();
        }

        abstract Pizza build();

        // Подклассы должны перекрывать этот метод, возвращая "себя"
        protected abstract V self();
    }

    Pizza(Builder<?> builder) {
        toppings = builder.toppings.clone();
    }
}

class NyPizza extends Pizza {

    private boolean sauceInside;

    public static class Builder extends Pizza.Builder<Builder> {

        private boolean sauceInside = false;

        public Builder sauceInside() {
            sauceInside = true;
            return this;
        }

        @Override
        NyPizza build() {
            return new NyPizza(this);
        }

        @Override
        protected Builder self() {
            return this;
        }
    }

    NyPizza(Builder builder) {
        super(builder);
        sauceInside = builder.sauceInside;
    }
}

class test {
    public static void main(String[] args) {
        NyPizza nyPizza = new NyPizza.Builder()
                .addTopping(Pizza.Topping.HAM)
                .sauceInside()
                .build();
    }
}