嵌套枚举构造函数

Question

我不确定我是否过度工程化了，但我正在考虑创建一个枚举，其中包含一个枚举列表作为它的值，从中我可以得到它的值。

enum Country {
  US(UnitedStates.values()),
  CA(Canada.values());

  public ? list;

  Country(? list) { this.list = list; }
}
enum UnitedStates {
  NJ(new NJClass()),
  PA(new PAClass());

  private BaseKlass klass;
  UnitedStates(BaseClass name){ this.klass = name }
  public BaseKlass getKass() { return klass; }
}
enum Canada {
  ON(new ONClass());

  private BaseKlass klass;
  Canada(BaseKlass name){ this.klass = name }

  public BaseKlass getKass() { return klass; }
}

我无法确定Country枚举的类型，以便正确地将值数组筛选到正确的枚举。例如，我可以用Country.valueOf（"US"）轻松地获得US枚举。我遇到的困难是从该数组中获得正确的值。我尝试比较名称，Country.valueOf（"US"）. stream（）. Filter（e-

这是可能的还是我想得太多了？




Answer 1

考虑到您不能让Enum扩展一些定制的父类来实现所需的抽象，我将遵循以下方法

public enum States {

    ALABAMA("Alabama", Country.US),
    ARIZONA("Arizona", Country.US),
    ON("Ontario", Country.CA),
    QC("Quebec", Country.CA),
    NS("Nova Scotia", Country.CA);

    States(String name, Country country){
        this.name = name;
        this.country = country;
    }

    private String name;
    private Country country;

    public List<States> getByCountry(Country country){
        return Arrays.stream(States.values()).filter(s -> s.country.equals(country)).collect(Collectors.toList());
    }
}

您还可以在初始化期间将这些状态保存在内存中，这样就不会每次都计算哪些状态属于哪个国家。

public enum States {

    ALABAMA("Alabama", Country.US),
    ARIZONA("Arizona", Country.US),
    ON("Ontario", Country.CA),
    QC("Quebec", Country.CA),
    NS("Nova Scotia", Country.CA);

    States(String name, Country country){
        this.name = name;
        this.country = country;
    }

    private String name;
    private Country country;

    private static Map<Country, List<States>> statesMap = initializeStatesMap();
    private static Map<Country, List<States>> initializeStatesMap(){
        return Arrays.stream(States.values())
                .collect(Collectors.groupingBy(state -> state.country,
                        Collectors.mapping(state -> state, Collectors.toList())));
    }

    public static List<States> getByCountry(Country country){
        return statesMap.containsKey(country) ? statesMap.get(country) : new ArrayList<>();
    }
}

然后呢

public enum Country {

    US,
    CA

}

Answer 2

绝对是过度工程化了。。。我会和你一起去的

enum Country {
  US(<array/list of us states is enough>),
  CA(<array/list of ca states is enough>);

  public List<State> list;

  Country(List<State> list) { this.list = list; }
}