Intro to Regular Expressions (Pattern Matching)

This lesson covers the basics of pattern matching using regular expressions in Java, so you can check whether a string matches a specific format. It's for anyone searching "Java regular expression usage."

A regular expression is a special syntax that describes a string's "shape." You can specify a pattern — like "3 digits, dash, 4 digits" — to check whether a string matches it, or extract matching parts. Use the Pattern and Matcher classes.

The example compiles a phone-number-like pattern with Pattern.compile(...).matcher(text), finds a match with m.find(), and extracts it with m.group(). There's also a simpler way to check with a string's own method, like "12345".matches("^\d+$").

A common early mistake is learning the meaning of the special symbols specific to regular expressions. It feels like a wall of confusing symbols at first, but it's a genuinely powerful tool for real work — like validating an email address's format.

In real projects, regular expressions are a widely valued skill precisely because, once learned, the same syntax carries over to most other programming languages.

📖 Reference code

String text = "Phone: 090-1234-5678";
Matcher m = Pattern.compile("\\d{3}-\\d{4}-\\d{4}").matcher(text);
if (m.find()) {
    System.out.println(m.group());
}
System.out.println("12345".matches("^\\d+$"));

✍️ Your code

Type your code, then press "Run"

🧪 This site can't compile or run Java directly, so it checks on the spot whether what you typed matches the reference code (scoring happens entirely in your browser — nothing is sent anywhere).