Why does this Java regex cause "illegal escape character" errors?

Question

I'm working on a solution to a previous question, as best as I can, using regular expressions. My pattern is

"\d{4}\w{3}(0[1-9]|[12][0-9]|3[01])([01][0-9]|2[0-3])([0-5][0-9]){2}"

According to NetBeans, I have two illegal escape characters. I'm guessing it has to do with the \d and \w, but those are both valid in Java. Perhaps my syntax for a Java regular expression is off...

The entire line of code that is involved is:

userTimestampField = new FormattedTextField(
  new RegexFormatter(
    "\d{4}\w{3}(0[1-9]|[12][0-9]|3[01])([01][0-9]|2[0-3])([0-5][0-9]){2}"
));

The pattern is definitly legal for java, it works in eclipse. Sorry im not with NetBeans. — Christopher Klewes
– Christopher Klewes, Commented Sep 4, 2009 at 13:19
Interesting. I'm adding the entire line of code to my question and I'll try to build, even with the error...let's see what happens. — Thomas Owens
– Thomas Owens, Commented Sep 4, 2009 at 13:23
You use it in string, think of escaping \d and \w with \\d and \\w — Christopher Klewes
– Christopher Klewes, Commented Sep 4, 2009 at 13:25

butterchicken · Accepted Answer · 2013-12-18 09:01:18Z

98

Assuming this regex is inside a Java String literal, you need to escape the backslashes for your \d and \w tags:

"\\d{4}\\w{3}(0[1-9]|[12][0-9]|3[01])([01][0-9]|2[0-3])([0-5][0-9]){2}"

This gets more, well, bonkers frankly, when you want to match backslashes:

public static void main(String[] args) {        
    Pattern p = Pattern.compile("\\\\\\\\"); //ERM, YEP: 8 OF THEM
    String s = "\\\\";
    Matcher m = p.matcher(s);
    System.out.println(s);
    System.out.println(m.matches());
}

\\ //JUST TO MATCH TWO SLASHES :(
true

edited Dec 18, 2013 at 9:01

answered Sep 4, 2009 at 13:23

butterchicken

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Comments

Alan Moore · Accepted Answer · 2009-09-04 17:33:36Z

15

Did you try "\\d" and "\\w"?

-edit- Lol I posted the right answer and get down voted and then I notice that stackoverflow escapes backslashes so my answer appeared wrong :)

edited Sep 4, 2009 at 17:33

Alan Moore

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answered Sep 4, 2009 at 13:22

willcodejavaforfood

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1 Comment

Alan Moore Over a year ago

The way I see it, you got downvoted for not making effective use of SO's code-formatting capability. ;)

asalamon74 · Accepted Answer · 2009-09-04 13:23:03Z

9

What about the following: \\d{4}\\w{3}(0[1-9]|[12][0-9]|3[01])([01][0-9]|2[0-3])([0-5][0-9]){2}

answered Sep 4, 2009 at 13:23

asalamon74

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2 Comments

Thomas Owens Over a year ago

This gets rid of the error...let's see if it actually works as a regex.

Thomas Owens Over a year ago

It appears to be working. +1. However, I accepted butterchicken's answer because it's more in-depth. Thanks for your help, though.

Melquiades · Accepted Answer · 2016-12-08 23:33:57Z

3

Have you tried this?

\\d{4}\\w{3}(0[1-9]|[12][0-9]|3[01])([01][0-9]|2[0-3])([0-5][0-9]){2}

edited Dec 8, 2016 at 23:33

Melquiades

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answered Sep 4, 2009 at 13:24

Christopher Klewes

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Comments

snaveware · Accepted Answer · 2022-09-14 06:30:32Z

1

I had a similar because I was trying to escape characters such as -,*$ which are special characters in regular expressions but not in java.

Basically, I was developing a regular expression https://regex101.com/ and copy pasting it to java.

I finally realized that because java takes regex as string literals, the only characters that should be escaped are the special characters in java ie. \ and "

So in this case \\d should work. However, anyone having a similar problem like me in the future, only escaped double quotes and backslashes.

edited Sep 14, 2022 at 6:30

answered Sep 14, 2022 at 6:29

snaveware

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1 Comment

Bouramas Over a year ago

This does not really answer the question. If you have a different question, you can ask it by clicking Ask Question. To get notified when this question gets new answers, you can follow this question. Once you have enough reputation, you can also add a bounty to draw more attention to this question. - From Review

Daniel · Accepted Answer · 2015-02-12 01:12:54Z

0

all you need to do is to put

 *\
 ex: string ex = 'this is the character: *\\s';

before your invalid character and not 8 \ !!!!!

answered Feb 12, 2015 at 1:12

Daniel

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Comments

MystikSpiral · Accepted Answer · 2009-09-04 13:22:51Z

-1

I think you need to add the two escaped shortcuts into character classes. Try this: "[\d]{4}[\w]{3}(0[1-9]|[12][0-9]|3[01])([01][0-9]|2[0-3])([0-5][0-9]){2}"

--Good Luck.

answered Sep 4, 2009 at 13:22

MystikSpiral

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1 Comment

Alan Moore Over a year ago

@MystikSpiral: \d and \w are character classes. They're shorthands (not "shortcuts") for the predefined character classes [0-9] and [A-Za-z0-9_] respectively. The brackets are redundant unless you're using them in combinations, like [\d\s] or [\w,.!?].

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