Java Regex — Free Java Tutorial

TL;DR: Learn Java Regex in Java with a free, beginner-friendly tutorial, examples and practice for Indian students on Syllab.in.

Java Regex in Java

Regular expressions (regex) are patterns for matching, searching, and manipulating text. Java provides them through java.util.regex (Pattern, Matcher) and String methods.

Common patterns: \d (digit), \w (word char), \s (whitespace), . (any char), * (0+), + (1+), ? (0 or 1), {n} (exactly n), {n,m} (n to m), ^ (start), $ (end), [] (character class), | (or), () (group).

Pattern.compile() compiles the regex (expensive — cache it). Matcher checks the pattern against input: matches() (full match), find() (substring match), group() (captured group).

String shortcuts: s.matches(regex), s.replaceAll(regex, replacement), s.split(regex) — these create a new Pattern each call, so use Pattern.compile() in loops.

import java.util.regex.*;

Pattern p = Pattern.compile("\\d{3}-\\d{4}");
Matcher m = p.matcher("Call 555-1234 now");
while (m.find()) {
    System.out.println("Found: " + m.group()); // 555-1234
}

// String shortcuts
"hello123".matches("[a-z]+\\d+");  // true
"a1b2c3".replaceAll("\\d", "X");  // "aXbXcX"
"a,b,,c".split(",+");               // ["a","b","c"]

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