Invalid escape sequence

Question

I would like to filter out all words containing 1 number and 3 capital letters with a total length of 4. See my example here: http://gskinner.com/RegExr/?32taa

ArrayList<String> result = new ArrayList<String>();


for(int i = 0; i <= 10; i++){

    String message = resp.data.get(i).message;

    Matcher m = MY_PATTERN.matcher("\b(?=[^\d]*\d[^\d]*)[A-Z\d]{4}\b");

        while (m.find()) {
            String s = m.group(1);
            result.add(s);
        }
}

But when i pass my regexp pattern to the matcher method, i get the error:

Invalid escape sequence (valid ones are  \b  \t  \n  \f  \r  \"  \'  \\ )

Do I need to swap \d with another letter?

Kumar Vivek Mitra · Answer 1 · 2012-11-25T18:26:59.853

5

Regex don't go well with String...

So u need to use \\d instead of \d

- When you write \ java expects either n or b or t or a and few others... after it, but when you give d it gets the shock of its life, and think what the hell.. i don't know nothing about \d, So we need to tell java that \ should be taken literally by it instead of expecting it as escape character.

- In the case of . (dot) it becomes even more complicated, when you give "." java takes it literally but its a regex so you need to make it look like that so you prefix it with \, so it becomes \. , now again the same problem as the earlier one begins as now java accepts n or b etc after \ but it gets a ".", so we again prefix it with another \, so now it becomes \\.

edited Nov 25 '12 at 18:26

answered Nov 25 '12 at 18:20

Kumar Vivek Mitra

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Nice answer :D "it gets the shock of its life" – AmShaegar Nov 25 '12 at 18:29
Some one just down voted this answer.... if possible please help me with reason..that would be very kind...and i will be able to improve this in a much better way.... – Kumar Vivek Mitra Nov 25 '12 at 18:43

score 4 · Answer 2 · edited Nov 25 '12 at 18:22

4

In Java, you need to escape the backslash with an extra backslash, when representing the pattern in string.

So, \b should be \\b, and \d should be \\d.

edited Nov 25 '12 at 18:22

bmargulies

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answered Nov 25 '12 at 18:20

Rohit Jain

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@Downvoter.. Any reason for downvote, you would like to quote? – Rohit Jain Nov 25 '12 at 19:00

score 3 · Accepted Answer · answered Nov 25 '12 at 18:22

3

Your code has two issues:

Your pattern is wrong, as it allows more digits - see http://regexr.com?32u3e
Java requires double escape slashes...

Use regex pattern

\\b(?=[A-Z]*\\d[A-Z]*\\b)[A-Z\\d]{4}\\b

answered Nov 25 '12 at 18:22

Ωmega

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Thanks for notifying me about the pattern as well. – Johan Nov 25 '12 at 18:39

Invalid escape sequence

3 Answers3

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