The escape character "\" in the Java string

In the Java string, if a slash appears,
1, as the escape character "\", the following must be followed by octal digits for ASCII escape output into other characters,
2, as a string slash direct output, you must use the double slash "\" escaped as a single slash

ASCII Reference octal table:
Https://baike.baidu.com/item/ASCII/309296?fr=aladdin

A special point in Java is: Str.split ("Sep", limit) function
The 1th parameter of the seperator delimiter string is to be parsed by the regular, so a special delimiter character is encountered and needs to be escaped again, for example. + ? * \：
. ---------- "\\."

+ ---------- "\\+"

? ---------- "\\?"

* ---------- "\\*"

\ ---------- "\\\\"

The escape character "\" in the Java string