REGEX

Question

Can anybody explain me this regex step by step?
String output = output.replaceAll("(?<=[^//b^])([A-Z])", "_$1").toLowerCase();

Answer 1

output must be initialised before use it, so
String output = "ABCDEFGHX /X/XbX^X";
output = output.replaceAll("(?<=[^//b^])([A-Z])", "_$1").toLowerCase();
System.out.println(output);
([A-Z])
() catch to group $1
[A-Z] upper case character of ALPHABET
(?<=[^//b^])
(?<= ) but before it, (positive lookBehind)
[^ ] can't be (character, but not one of this..)
//b^ one of this characters: / or / or b or ^
.replaceAll(this.., with "_$1")
_$1 _ and something in catch group $1
.toLowerCase() convert everything to lower case