How Do I Match Literal Characters in Java RegEx?

Understanding Metacharacters and Ordinary Characters in Java RegEx

In Java RegEx, the dot character (.) has a dual role, serving both as a metacharacter and an ordinary character. This distinction can be a source of confusion for new users.

Metacharacters vs. Ordinary Characters

Metacharacters have special meanings within a regular expression. For example, the dot metacharacter matches any single character, while the asterisk (*) metacharacter matches zero or more repetitions of the preceding pattern.

In contrast, ordinary characters retain their literal meaning. For instance, the '.' character outside of a regular expression would simply represent a period.

Handling Metacharacters in Java RegEx

To use a metacharacter as an ordinary character, it must be escaped with a backslash (). This is because regular expressions in Java are stored as strings. Therefore, to represent a literal backslash, you need to escape it with another backslash.

For example, to match a literal period, use \. instead of . Same applies for other metacharacters.

Example:

String text = "This is a sample string.";

// Matches the literal period using an escaped metacharacter
Pattern pattern = Pattern.compile("Th\\.is");
Matcher matcher = pattern.matcher(text);

if (matcher.find()) {
    System.out.println("Match found: " + matcher.group());
}

By following these guidelines, you can distinguish between metacharacters and ordinary characters in Java RegEx and handle them effectively.

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