Java Collection - 如何创建String到超类类型映射

import java.util.HashMap;
import java.util.Map;

class Pizza {
}

class CheesePizza extends Pizza {
}

class VeggiePizza extends Pizza {
}

public class Main {

  public static void main(String... args) {
    Map<String, Pizza> pizzaStock = new HashMap<String, Pizza>();

    pizzaStock.put("cheese", new CheesePizza());
    pizzaStock.put("veggie", new VeggiePizza());
    System.out.println(pizzaStock);
  }
}