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

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Answer 1

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 2

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 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