Explain this line written in JAVA

Skip \r\n is for Windows.

The rest is standard \r=CR, \n=LF (see \r\n , \r , \n what is the difference between them?)

Then some Unicode special characters:

u2028 = LINE SEPARATOR (https://www.fileformat.info/info/unicode/char/2028/index.htm)

u2029 = PARAGRAPH SEPARATOR (http://www.fileformat.info/info/unicode/char/2029/index.htm)

u0085 = NEXT LINE (https://www.fileformat.info/info/unicode/char/0085/index.htm)

Scanner.skip skips a input which matches the pattern, here the pattern is :-

(\r\n|[\n\r\u2028\u2029\u0085])?

? matches exactly zero or one of the previous character.
| Alternative
[] Matches single character present in
\r matches a carriage return
\n newline
\u2028 matches the character with index 2018 base 16(8232 base 10 or 20050 base 8) case sensitive
\u2029 matches the character with index 2029 base 16(8233 base 10 or 20051 base 8) case sensitive
\u0085 matches the character with index 85 base 16(133 base 10 or 205 base 8) case sensitive

1st Alternative \r\n

2nd Alternative [\n\r\u2028\u2029\u0085]

Match a single character present in the list below [\n\r\u2028\u2029\u0085]
\n matches a line-feed (newline) character (ASCII 10)
\r matches a carriage return (ASCII 13)
\u2028 matches the character with index 202816 (823210 or 200508) literally (case sensitive) LINE SEPARATOR
\u2029 matches the character with index 202916 (823310 or 200518) literally (case sensitive) PARAGRAPH SEPARATOR
\u0085 matches the character with index 8516 (13310 or 2058) literally (case sensitive) NEXT LINE