Matching
Description
matches checks whether all text fits a pattern.
Explanation
Use escaped backslashes in Java strings for regex escapes.
Example
boolean digits = "123".matches("\\d+");← Chapter 9 — Files & Regular Expressions
33. Regular Expressions
mixed
Description
Regular expressions describe patterns in text. In Java, String methods and the Pattern API can use them to search, split, replace, or validate input.
Start with small patterns and test them with realistic examples. A regex that is clever but unreadable is difficult to maintain.
Subtopics
Finding patterns
Description
Pattern and Matcher can locate parts of text.
Explanation
find searches within longer input.
Example
java.util.regex.Pattern.compile("Java").matcher("Learn Java").find();Explanation
A Java string literal adds its own escaping layer. The regex \d is written as "\\d" in Java source because the first backslash escapes the second for the String.
Example
public class RegexDemo {
public static void main(String[] args) {
String rollNumber = "STU-104";
boolean valid = rollNumber.matches("STU-\\d{3}");
System.out.println(valid);
}
}Key points
- Regexes describe text patterns.
- matches checks the entire string.
- Backslashes are escaped in Java strings.