How to Efficiently Retrieve All Regex Matches as an Array in Java?

Retrieve Regex Matches as an Array

In Java, determining whether a given pattern matches a specific string is straightforward. However, when handling multiple matches, it can be challenging to collect them into an array. To address this, delve into this guide to discover how to utilize regex matches effectively.

Iterative Approach

To accumulate matches into an array, leverage a combination of Matcher and String:

import java.util.regex.Matcher;
import java.util.regex.Pattern;

...

List<string> allMatches = new ArrayList();
Matcher m = Pattern.compile("your regular expression here")
    .matcher(yourStringHere);
while (m.find()) {
  allMatches.add(m.group());
}</string>

This code establishes a Matcher object that systematically finds matching substrings within the input string. Each successful match is appended to the allMatches list. Finally, convert it to an array using allMatches.toArray(new String[0]):

String[] matchesArr = allMatches.toArray(new String[0]);

Custom Iterable for Lazier Matches

Alternatively, consider implementing a lazy iterator to traverse and immediately consume matches without unnecessary processing:

public static Iterable<matchresult> allMatches(
    final Pattern p, final CharSequence input) {
  return new Iterable<matchresult>() {
    public Iterator<matchresult> iterator() {
      return new Iterator<matchresult>() {
        // Internal Matcher
        final Matcher matcher = p.matcher(input);
        // Lazy-filled MatchResult
        MatchResult pending;

        public boolean hasNext() {
          if (pending == null && matcher.find()) {
            pending = matcher.toMatchResult();
          }
          return pending != null;
        }

        public MatchResult next() {
          if (!hasNext()) { throw new NoSuchElementException(); }
          MatchResult next = pending;
          pending = null;
          return next;
        }

        public void remove() { throw new UnsupportedOperationException(); }
      };
    }
  };
}</matchresult></matchresult></matchresult></matchresult>

Employ it as follows:

for (MatchResult match : allMatches(
    Pattern.compile("[abc]"), "abracadabra")) {
  System.out.println(match.group() + " at " + match.start());
}

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