REGEX

Java Regular Expressions

Learn how to match patterns in text using Java's powerful regular expression engine. Experiment interactively and explore common constructs.

Common Regex Constructs

Java uses a Perl-like syntax for regular expressions. These are the core pieces you'll use most often when building patterns:

Character Classes

[abc] – matches a, b or c.
[^abc] – matches any character except a, b or c.
[a-zA-Z] – matches a letter from a to z or A to Z.
[a-d[m-p]] – matches a through d or m through p (union).
[a-z&&[def]] – matches d, e or f (intersection).
[a-z&&[^bc]] – matches letters except b and c (subtraction).

Predefined Character Classes

\d – matches a digit (0–9).
\D – matches a non-digit.
\s – matches a whitespace character (space, tab, newline).
\S – matches a non-whitespace character.
\w – matches a word character (letters, digits, underscore).
\W – matches a non-word character.

Quantifiers

? – the preceding element is optional (zero or one time).
* – the preceding element can appear zero or more times.
+ – the preceding element must appear one or more times.
{n} – appears exactly n times.
{n,} – appears at least n times.
{n,m} – appears between n and m times.

Boundary Matchers

^ – matches the beginning of a line.
$ – matches the end of a line.
\b – matches a word boundary.
\B – matches a non-word boundary.

Interactive Regex Tester

Enter a regex pattern and test it against your own string. We'll highlight the matches and break down each part of the pattern.

Regex Pattern:

Test String:

Result (Highlighted Text):

Java is a programming language. JavaScript is not Java.

Matches Found:

Match 1 at index 0: Java

Match 2 at index 50: Java

Regex Explanation

A simple breakdown of the components in your current pattern:

\bJava\b

`\b`: Matches a word boundary.