Java Regex: How to Escape Special Characters

Regular expressions, or regex, are widely used in Java programming to match patterns in text. However, some characters are considered special characters in regex and need to be escaped in order to be treated as literal characters. In this article, we will discuss how to escape special characters in Java regex.

Escape Characters in Java Regex

There are several special characters in Java regex, including:

• . - Matches any character except newline.
• * - Matches zero or more occurrences of the preceding character.
• + - Matches one or more occurrences of the preceding character.
• ? - Matches zero or one occurrence of the preceding character.
• | - Matches either the expression before or after the pipe character.
• () - Groups expressions together.
• [] - Matches any single character in the brackets.
• {} - Matches a specific number of occurrences of the preceding character.
• - Escapes special characters.

In order to use these special characters as literal characters in Java regex, we need to escape them using the character. For example, to match a period character, we would use the regex . instead of just ..

Examples

Here are some examples of how to escape special characters in Java regex:

String regex = "Hello\+World";
String input = "Hello+World";
boolean matches = input.matches(regex);
// matches = true

In the example above, we want to match the literal string Hello+World, so we need to escape the + character with a .

String regex = "\d\{3\}-\d\{2\}-\d\{4\}";
String input = "123-45-6789";
boolean matches = input.matches(regex);
// matches = true

In this example, we want to match a social security number in the format XXX-XX-XXXX, so we need to escape the {} characters with a .

Conclusion

Escaping special characters is an important technique when working with Java regex. By using the character, we can treat special characters as literal characters in our regex patterns. Remember to always escape special characters when necessary to avoid unexpected behavior in your regex matches.