Pattern.compile() / Matcher.matches() / find()

// Compile a regular expression and create a Pattern object.
Pattern p = Pattern.compile(String regex);
Pattern p = Pattern.compile(String regex, int flags);

// Create a Matcher object for the given string.
Matcher m = p.matcher(CharSequence input);

// Check whether the entire string matches the pattern.
boolean result = m.matches();

// Search for the next substring that matches the pattern.
boolean found = m.find();

// Get the string matched by the most recent find() or matches() call.
String matched = m.group();
String matched = m.group(int group);

import java.util.regex.*;

// Use matches() to check whether a string is in postal code format.
Pattern p = Pattern.compile("\\d{3}-\\d{4}");
Matcher m = p.matcher("123-4567");
System.out.println(m.matches()); // Prints 『true』.

// Use find() to extract all email addresses from a string.
String text = "Contact: alice@example.com or bob@test.jp.";
Pattern emailPattern = Pattern.compile("[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,}");
Matcher emailMatcher = emailPattern.matcher(text);
while (emailMatcher.find()) {
    System.out.println(emailMatcher.group()); // Prints 『alice@example.com』 then 『bob@test.jp』.
}

// Use group() to extract capture groups.
Pattern datePattern = Pattern.compile("(\\d{4})-(\\d{2})-(\\d{2})");
Matcher dateMatcher = datePattern.matcher("Today is 2026-03-05.");
if (dateMatcher.find()) {
    System.out.println(dateMatcher.group(1)); // Prints 『2026』.
    System.out.println(dateMatcher.group(2)); // Prints 『03』.
    System.out.println(dateMatcher.group(3)); // Prints 『05』.
}

// Use the CASE_INSENSITIVE flag to ignore case.
Pattern casePattern = Pattern.compile("java", Pattern.CASE_INSENSITIVE);
Matcher caseMatcher = casePattern.matcher("Java is a general-purpose language.");
System.out.println(caseMatcher.find()); // Prints 『true』.

Pattern.compile() compiles a regular expression string into a reusable Pattern object. When the same pattern is used repeatedly, reusing a compiled Pattern improves performance.

matches() checks whether the entire string matches the pattern, while find() searches for matching substrings one at a time. matches() requires a full-string match, whereas find() performs partial matching. Choose the one that fits your intent.

To replace matches using a regular expression, use Matcher.replaceAll() / replaceFirst().