What's the Difference Between the Normal Dot (.) and the Metacharacter Dot (.) in Java Regular Expressions?

Java Regular Expression Meta Character (.) vs. Ordinary Dot

In Java RegEx, both the normal dot (.) and the meta character (.) appear. However, they represent different concepts.

Normal Dot

The normal dot matches a single character in a string. For example, the regex "a.b" matches the strings "a1b", "a3b", and "a@b".

Metacharacter Dot

The metacharacter dot is a special character that matches any character except line breaks. This includes special characters, such as spaces, punctuation, and brackets. For instance, the regex "a(. )b" matches the string "a 123 b" but not "anb" (which contains a line break).

Escaping Metacharacters

To treat a metacharacter as a normal character, it must be escaped with a backslash (). For instance, if you want to match a period (.) literally, you would use the regex "a.b". This escapes the dot, indicating that you're searching for the character "." rather than the metacharacter that matches any character.

Escaping Other Metacharacters

The same principle applies to other metacharacters in RegEx. For example:

• : Escaped as to match the literal plus sign ( )
• : Escaped as to match the literal asterisk (*)
• d: Escaped as \d to match any digit
• [abc]: Escaped as [abc] to match any character in the square brackets (e.g., "a", "b", or "c")

By escaping metacharacters with double backslashes (), you can ensure they are treated as normal characters in your RegEx patterns.

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