Does Java Actually Escape Back Slashes how it claims?

What I understand is that every backslash requires one more backslash to be escaped for regex. I have the following input String in Java:

C:\\my\\drive\\application\\webapps\\ROOT\\classes\\there\\is\\a\\clazz

to remove everything upto classes\\, I added the following regex in Java replaceAll() method:

.*\\\\b(classes)(\\\\W\\\\S|\\\\/){1,2}\\\\b

Why i have added four slashes

1. One backslash escaped to indicate that this is regex \\

2. One backslash escaped to indicate that the regex input is going as a java String \\.

But even with one set of doubled-backslash \\ it doesn't work.

When I tried it on regexr and regexplanet, it seems to be working correctly for both unix/windows type of filepaths and gave me what I wanted. It showed me the correct replaceAll() results as desired.

But when I put it into the code, it's not working at all.

So how many times in Java do we need to actually escape each backslash to get this to work?