Java regex "[.]" vs "."

Question

I'm trying to use some regex in Java and I came across this when debugging my code.

What's the difference between [.] and .?

I was surprised that .at would match "cat" but [.]at wouldn't.

Did you go through any regex tutorial? `.` is a meta-character which matches anything except a newline. Inside a character class, it isn't a meta-character. — Rohit Jain, Sep 05 '13 at 15:33
Yes, I have been looking at the oracle tutorials. `[abc]` is a character class that matches a, b, or c. So why doesn't `[.]` act the same as `.`? — GDanger, Sep 05 '13 at 15:34
ahh, I didn't understand that inside it's own character class it's no longer a meta-character. Thank you. — GDanger, Sep 05 '13 at 15:35

score 20 · Accepted Answer · edited Sep 27 '13 at 17:41

20

[.] matches a dot (.) literally, while . matches any character except newline (\n) (unless you use DOTALL mode).

You can also use \. ("\\." if you use java string literal) to literally match dot.

edited Sep 27 '13 at 17:41

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answered Sep 05 '13 at 15:33

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Any character, but the new-line one (by default at least ;) – sp00m Sep 05 '13 at 15:35

score 4 · Answer 2 · edited May 23 '17 at 12:10

The [ and ] are metacharacters that let you define a character class. Anything enclosed in square brackets is interpreted literally. You can include multiple characters as well:

[.=*&^$] // Matches any single character from the list '.','=','*','&','^','$'

There are two specific things you need to know about the [...] syntax:

The ^ symbol at the beginning of the group has a special meaning: it inverts what's matched by the group. For example, [^.] matches any character except a dot .
Dash - in between two characters means any code point between the two. For example, [A-Z] matches any single uppercase letter. You can use dash multiple times - for example, [A-Za-z0-9] means "any single upper- or lower-case letter or a digit".

The two constructs above (^ and -) are common to nearly all regex engines; some engines (such as Java's) define additional syntax specific only to these engines.

You can find [character class union/intersection/substraction](http://stackoverflow.com/a/3201747/1225328) too actually ;) — sp00m, Sep 05 '13 at 15:47
@sp00m That's true - thanks, I edited the answer to mention it. — Sergey Kalinichenko, Sep 05 '13 at 15:51

score 1 · Answer 3 · answered Dec 07 '21 at 06:17

regular-expression constructs

. => Any character (may or may not match line terminators)

and to match the dot . use the following

[.] => it will matches a dot
\\. => it will matches a dot

NOTE: The character classes in Java regular expression is defined using the square brackets "[ ]", this subexpression matches a single character from the specified or, set of possible characters.

Example : In string address replaces every "." with "[.]"

public static void main(String[] args) {
    String address = "1.1.1.1";
    System.out.println(address.replaceAll("[.]","[.]"));
}

if anything is missed please add :)

Java regex "[.]" vs "."

3 Answers3