java - Java 中的嵌套枚举？

Question

我想为我的 Web 应用程序中可用的各种 ajax 服务定义一些枚举，例如:

Enum Service
{
    REGISTER,
    LOGIN,
    NEWS,
    FAQ
}

但是，这些枚举中的每一个也会有特定的状态，如失败、加载等。所以我希望能够使用 REGISTER.LOADED、LOGIN.LOADED 等等，在我的事件总线上启动事件。但是每个状态枚举必须是唯一的。即 Register.LOADED 必须不同于 FAQ.LOADED，等等。

编辑:此外，我必须能够将所有状态存储在同一 HashMap 中，例如 Register.LOADED 和 Login.LOADED 必须可存储在同一 HashMap 中。并且父服务枚举，即 LOGIN、REGISTER 等也必须可存储在同一个 HashMap 中。

完成此任务的最佳方法是什么？

Answer 1

在 OP 的一些评论之后，我更新了我的代码。使用语法变得丑陋，在 switch 中可能效果不佳 block ，但我相信这实现了 OP 正在寻找的东西:

import java.util.*;

public class HelloWorld
{
    public static void main(String []args)
    {
        // Different services are not equal
        System.out.println(Service.REGISTER + "==" + Service.LOGIN + " :: " + Service.REGISTER.equals(Service.LOGIN));
        // Same service is equal
        System.out.println(Service.REGISTER + "==" + Service.REGISTER + " :: " + Service.REGISTER.equals(Service.REGISTER));
        // Even after changing the state
        Service tmp = Service.REGISTER;
        Service.REGISTER.setState(Service.ServiceState.State.FAILED);
        System.out.println(Service.REGISTER + "==" + tmp + " :: " + Service.REGISTER.equals(tmp));
        
        Service.REGISTER.setState(Service.ServiceState.State.LOADED);
        
        // Different service, same state is not equal
        System.out.println(Service.REGISTER + "." + Service.REGISTER.state + "==" + Service.LOGIN + "." + Service.LOGIN.state + " :: " + Service.REGISTER.state.equals(Service.LOGIN.state));
        
        // Same service, same state is equal (even when changing state around)
        Service.ServiceState.State temp = Service.REGISTER.getState();
        Service.REGISTER.setState(Service.ServiceState.State.LOADED);
        System.out.println(Service.REGISTER + "." + Service.REGISTER.state + "==" + tmp + "." + temp + " :: " + temp.equals(Service.REGISTER.getState()));
        
        // Same service, different state is not equal
        Service.REGISTER.setState(Service.ServiceState.State.FAILED);
        System.out.println(Service.REGISTER + "." + Service.REGISTER.state + "==" + tmp + "." + temp + " :: " + temp.equals(Service.REGISTER.getState()));
        
        // Both service and state can be used as map keys
        Map<Service, String> map = new HashMap<Service, String>();
        Map<Service.ServiceState.State, String> map2 = new HashMap<Service.ServiceState.State, String>();
    }
}

enum Service
{
    REGISTER(),
    LOGIN(),
    NEWS(),
    FAQ();

    public ServiceState state;

    Service()
    {
        this.state = new ServiceState();
    }
    
    public void setState(ServiceState.State s)
    {
        state.state = s;
    }
    
    public ServiceState.State getState() { return state.state; }

    public static class ServiceState
    {
        public enum State
        {
            LOADED,
            FAILED
        }
        
        public State state = State.LOADED;
        
        public ServiceState(){}
        
        public String toString() { return state.toString(); }
        
        public int hashCode()
        {
            return state.hashCode();
        }
        
        public boolean equals(Object obj)
        {
            return state.equals(obj);
        }
    }
}

输出:

REGISTER==LOGIN :: false
REGISTER==REGISTER :: true
REGISTER==REGISTER :: true
REGISTER.LOADED==LOGIN.LOADED :: false
REGISTER.LOADED==REGISTER.LOADED :: true
REGISTER.FAILED==REGISTER.LOADED :: false

---

原答案:

用你想要的语法不太可能，但 Java 枚举基本上只是类的另一个名字。 (事实上​​ ，一旦编译，它们是扩展 java.lang.Enum<E extends Enum<E>> 的类)

public class HelloWorld
{
    public static void main(String []args)
    {
        Service a = Service.REGISTER;
        a.state = Service.ServiceState.LOADED;
        System.out.println(a);
    }
}

enum Service
{
    REGISTER(),
    LOGIN(),
    NEWS(),
    FAQ();
    
    public ServiceState state;
    
    Service()
    {
        this.state = ServiceState.LOADED;
    }
    
    public String toString()
    {
        return super.toString() + "." + state.toString();
    }
    
    public enum ServiceState
    {
        LOADED,
        FAILED
    }
}

输出:

REGISTER.LOADED