the replaceFirst method of String & ????

[John Smith]

this is my code
String msg = "sub???".replaceFirst("\\?\\?\\?\\?\\?\\?\\?\\?\\?\\?\\?\\?\\?\\?\\?\\?", "2005012100362541");

why need tow "\\" ?

[Ken Blair]

replaceFirst() uses regular expressions. In regular expressions a ? has special meaning and you must use \? to indicate you mean the literal ?. However, in Java \ is an escape character as well and necessitates escaping the escape character resulting in a \\ to indicate a \ in the regular expression.

Also, a simplified version of that regular expression is "\\?{16}" which matches exactly 16 question marks.

[John Smith]

thank you very much