无效的转义序列

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?

Answer 1

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 \\\\.

Answer 2

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 .

Answer 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