java - 为什么不区分大小写的比较器不进行大小写比较

Question

这个问题已经有答案了:

Understanding logic in CaseInsensitiveComparator (5 个回答)

已关闭 7 年前。

我正在查看 CaseInsensitiveComparator 的代码，但无法理解以下代码

               if (c1 != c2) {
                c1 = Character.toUpperCase(c1);
                c2 = Character.toUpperCase(c2);
                if (c1 != c2) {
                    c1 = Character.toLowerCase(c1);
                    c2 = Character.toLowerCase(c2);
                    if (c1 != c2) {
                        // No overflow because of numeric promotion
                        return c1 - c2;
                    }
                }
            }

比较大小写字符的目的是什么？难道其中之一还不够吗？我们是否怀疑某些字符小写时可以相等，但大写时不相等？

Answer 1

来自Unicode Standard :

In addition, because of the vagaries of natural language, there are situations where two different Unicode characters have the same uppercase or lowercase

所以有时你会发现字母的小写相同而大写不同，从而进行比较。

另请检查source其中说:

Unfortunately, conversion to uppercase does not work properly for the Georgian alphabet, which has strange rules about case conversion. So we need to make one last check before exiting.