具有Java 8强大功能的String上的特殊顺序 [英] Special order on String with the power of Java 8

问题描述

我有一个有限的字符串列表（或数组）。此列表将通过以下方式描述我的新订单：字符串 s1 小于字符串 s2 iff之一接下来的三个语句成立

I've got a finite list (or array) of strings. This list shall describe my new order by the following means: A string s1 is less than a string s2 iff one of the next three statements holds

• 两者都在列表中 s1 有较低的列表中的索引比 s2


• 两者都不在列表中， s1 小于 s2 按字符串的自然顺序


• s1 在列表中， s2 不是

• both are in the list an s1 has a lower index in the list than s2
• both aren't in the list and s1 is less than s2 by the natural order on strings
• s1 is in the list and s2 is not

我想用的是电源Java 8编写一行Comparator。什么是最短的这条线？您可以假设我的列表是 ArrayList< String> 。

I want to use the power of Java 8 to write a one line Comparator. What is the shortest such line? You can assume my list to be an ArrayList<String>.

编辑：我不想订购我正在谈论的清单。我想使用该列表来定义一个允许我订购许多其他列表的订单。

I don't want to order the list I'm talking about. I want to use that list to define an order which allows me to order many other lists.

推荐答案

最短的比较器您可以获得的任务定义是：

The shortest Comparator definition you can get for your task is:

Comparator.comparingInt((String s) -> reference.indexOf(s)+Integer.MIN_VALUE)
          .thenComparing(Comparator.naturalOrder())

但它要求读者理解整数比较中的 + Integer.MIN_VALUE 习语。它基本上意味着执行无符号比较（另见 Integer.compareUnsigned（...） ），以便 -1 的值，由<返回对于缺席值，code> List.indexOf 被视为最高可能的数字，因此当前值的每个索引都被认为小于该值，以满足您的规范。

but it requires the reader to understand the +Integer.MIN_VALUE idiom in integer comparisons. It basically means "perform an unsigned comparison" (see also Integer.compareUnsigned(…)), so that the value -1, returned by List.indexOf for absent values, is treated as the highest possible number, so that every index of a present value is considered to be smaller than that, to meet your specification.

然后，您可以简单地链接另一个比较器，这里是自然顺序，对于两个索引都相同的情况，包括两者都不存在的可能性。

Then, you can simply chain another comparator, here the natural order, for the case both indices are the same, which includes the possibility that both are absent.

如果您认为读者难以理解无符号比较，则必须明确编码三种情况，如 tobias_k的回答。

If you think that the unsigned comparison is to hard to grasp for the reader, you have to encode your three cases explicitly, as already shown in tobias_k’s answer.

这篇关于具有Java 8强大功能的String上的特殊顺序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！