Regex in Java is a way to describe text patterns so you can search, validate, split, or replace parts of strings. Java supports it through the java.util.regex package, mainly with Pattern, Matcher, and PatternSyntaxException.

Quick Scoop

A regex is like a tiny language for matching text patterns. In Java, it is commonly used for things like email validation, password checks, log parsing, and text cleanup.

Main pieces

  • Pattern: stores the regex pattern you want to use.
  • Matcher: runs the pattern against a string and lets you search or replace.
  • PatternSyntaxException: appears when the regex itself has an error.

Simple example

java

import java.util.regex.Pattern;

public class Main {
    public static void main(String[] args) {
        boolean ok = Pattern.matches("\\d+", "12345");
        System.out.println(ok); // true
    }
}

This checks whether the whole string contains only digits. The \\d+ pattern means “one or more digits”.

Common uses

  • Validate input, such as phone numbers or emails.
  • Find text inside a larger string.
  • Replace patterns in text.
  • Split strings by separators like spaces, commas, or punctuation.

Tiny takeaway

In Java, regex is basically a powerful pattern-matching tool for strings. If you remember one thing, remember this: pattern + matcher = regex work in Java.

TL;DR: Regex in Java is a pattern language for text matching and manipulation, built mainly around Pattern and Matcher in java.util.regex.