如何用泛型实现枚举？ [英] How to implement enum with generics?

问题描述

我有一个这样的通用界面：

I have a generic interface like this:

interface A<T> {
    T getValue();
}

此接口有限的实例，因此最好将它们实现为枚举值。问题是这些实例具有不同类型的值，所以我尝试了以下方法，但是它不编译：

This interface has limited instances, hence it would be best to implement them as enum values. The problem is those instances have different type of values, so I tried the following approach but it does not compile:

public enum B implements A {
    A1<String> {
        @Override
        public String getValue() {
            return "value";
        }
    },
    A2<Integer> {
        @Override
        public Integer getValue() {
            return 0;
        }
    };
}

任何关于这个想法？

推荐答案

你不能。 Java不允许在枚举常量上使用通用类型。枚举类型允许使用枚举类型：

You can't. Java doesn't allow generic types on enum constants. They are allowed on enum types, though:

public enum B implements A<String> {
  A1, A2;
}

在这种情况下你可以做的是每个通用的枚举类型类型，或'假的'有一个枚举，只是使它成为一个类：

What you could do in this case is either have an enum type for each generic type, or 'fake' having an enum by just making it a class:

public class B<T> implements A<T> {
    public static final B<String> A1 = new B<String>();
    public static final B<Integer> A2 = new B<Integer>();
    private B() {};
}

不幸的是，他们都有缺点。

Unfortunately, they both have drawbacks.

这篇关于如何用泛型实现枚举？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！