Java Scanner backslash delimiter

Question

I try to use a series of delimiter for an input. It's for a homework. They said that we should use backslash () too. If I use it like this (it's at the end):

scanner.useDelimiter("\\;|\\:|\\?|\\~|/|\\.|,|\\<|\\>|\\`|\\[|\\]|\\{|\\}|\\(|\\)|\\!|\\@|\\#|\\$|\\%|\\^|\\&|\\-|\\_|\\+|\\'|\\=|\\*|\"|\\||\n|\t|\r|\\");

It won't work. It says unsupported escape sequence. If I add another backslash it says Illegal line end in string literal. If I add another it will escape to double backslash and that's not what I need.

I couldn't find any solution for this and that's why I'm asking. I already finished the homework and I used Scanner and right now changing it it's not a solution (a lot to re-implement).

Thank you.

@AvinashRaj like, using it as a regex expression, not string? — Matei, Nov 22 '15 at 11:02

Tamas Hegedus · Accepted Answer · 2015-11-22T12:07:59.097

You should use four backslashes at the end, like:

scanner.useDelimiter("\\;|\\:| ... |\r|\\\\");

This is the way it should work. You said if you tried it would match double backslashes. Have you tried it? If you did, and it still matches double backslashes, I suspect your input is escaped too somewhere. (maybe it is a string literal somewhere in your code?)

The reason behind this is that your string is de-escaped twice. Once at compile time as every other string literal in the Java language, and once compiling the regex. That means, after the first step it is escaped once, so the regex compiler gets two backslashes \\. The regex compiler will de-escape that too (just like \r), and will match a single \ character.

If you would like to match two backslashes this way, then you have to use eight backslash (\\\\\\\\ or \\\\{2}) in your literal. Yeah, pretty ugly.

Yeah, but I can't understand why I have to use four backslashes. If so, how do you escape two backslashes? :)) — Matei, Nov 22 '15 at 12:04
I did my best to answer your questions by modifying my answer :) — Tamas Hegedus, Nov 22 '15 at 12:10

score 0 · Answer 2 · edited May 23 '17 at 12:07

0

You are using the delimiter in wrong way i think.

There is a related topic.

Check this first

How do I use a delimiter in Java Scanner?

edited May 23 '17 at 12:07

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answered Nov 22 '15 at 11:48

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Java Scanner backslash delimiter

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