java -\uXXXX、\uuXXXX 和\uuuXXXX 之间的区别

Question

下一行来自JLS §3.3 :

If an eligible \ is followed by u , or more than one u , and the last u is not followedby four hexadecimal digits, then a compile-time error occurs.

所以这意味着下面几行的结果是一样的:

System.out.println('\u0065');   // prints "e"
System.out.println('\uu0065');  // prints "e"
System.out.println('\uuu0065'); // prints "e"

在 \uXXXX 中使用单个 u 与在 \uuXXXX 中使用 uu 本质上是一样的。我的问题是，为什么我们需要这种设计？

Answer 1

原因稍后在引用的部分中说明:

The Java programming language specifies a standard way of transforming a program written in Unicode into ASCII that changes a program into a form that can be processed by ASCII-based tools. The transformation involves converting any Unicode escapes in the source text of the program to ASCII by adding an extra u - for example, \uxxxx becomes \uuxxxx - while simultaneously converting non-ASCII characters in the source text to Unicode escapes containing a single u each.

这意味着它使到 ASCII 的转换完全可逆，因为您知道哪些转义序列最初在代码中，哪些是通过转换添加的。