在枚举类型上实现 `next` 和 `previous` 的最佳方法是什么? [英] What's the best way to implement `next` and `previous` on an enum type?

问题描述

假设我有一个枚举:

enum E {
    A, B, C;
}

如这个答案中所示，lucasmo，枚举值按照它们被初始化的顺序存储在一个静态数组中，你以后可以用 E.values() 检索(克隆)这个数组.

As shown in this answer by lucasmo, enum values are stored in a static array in the order that they are initialized, and you can later retrieve (a clone of) this array with E.values().

现在假设我想实现 E#getNext 和 E#getPrevious 使得以下所有表达式的计算结果为 true:>

Now suppose I want to implement E#getNext and E#getPrevious such that all of the following expressions evaluate to true:

E.A.getNext() == E.B
E.B.getNext() == E.C
E.C.getNext() == E.A

E.A.getPrevious() == E.C
E.B.getPrevious() == E.A
E.C.getPrevious() == E.B

我当前对 getNext 的实现如下:

My current implementation for getNext is the following:

public E getNext() {
    E[] e = E.values();
    int i = 0;
    for (; e[i] != this; i++)
        ;
    i++;
    i %= e.length;
    return e[i];
}

以及getPrevious的类似方法.

然而，这段代码充其量看起来很麻烦(例如，空"for 循环，有争议的滥用计数器变量，最坏的情况下可能是错误的(思考反射，可能).

However, this code seems cumbersome at best (e.g., "empty" for loop, arguable abuse of a counter variable, and potentially erroneous at worst (thinking reflection, possibly).

在 Java 7 中为枚举类型实现 getNext 和 getPrevious 方法的最佳方法是什么?

What would be the best way to implement getNext and getPrevious methods for enum types in Java 7?

注意:我不希望这个问题是主观的.我对最佳"实现的要求是要求最快、最干净和最易于维护的实现的简写.

NOTE: I do not intend this question to be subjective. My request for the "best" implementation is shorthand for asking for the implementation that is the fastest, cleanest, and most maintainable.

推荐答案

试试这个:

public static enum A { 
    X, Y, Z;
    private static A[] vals = values();
    public A next()
    {
        return vals[(this.ordinal()+1) % vals.length];
    }

previous() 的实现留作练习，但请记住 在Java中，模a % b可以返回一个负数.

Implementation of previous() is left as an exercise, but recall that in Java, the modulo a % b can return a negative number.

按照建议，制作 values() 数组的私有静态副本，以避免每次 next() 或 previous() 被调用.

As suggested, make a private static copy of the values() array to avoid array copying each time next() or previous() is called.

这篇关于在枚举类型上实现 `next` 和 `previous` 的最佳方法是什么?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！