How to Retrieve and Array of Matches from a String Using Java Regular Expressions?

Retrieve Matches Using Regular Expressions in Java

Obtaining an array of matches from a given string using regular expressions in Java involves creating a matcher and iterating over matches.

Using a Matcher

Create a Matcher object using the compile method of the Pattern class:

Matcher m = Pattern.compile("regex_expression").matcher(input_string);

Iterating over Matches

Use the find method of the Matcher to iterate over matches:

List<string> allMatches = new ArrayList();
while (m.find()) {
  allMatches.add(m.group());
}</string>

Converting to Array

If you need an array of matches, use the toArray method:

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

Enhanced Methods with MatchResult (Java >= 9)

In Java 9 and above, you can use the toMatchResult method on a Matcher to create a MatchResult object. This provides methods to create lazy iterators for efficient looping over matches:

for (MatchResult match : MatchResult.findAll(p, input)) {
  // Use match information without advancing iteration...
}

For example, this code uses the allMatches helper method to iterate over matches, printing their groups and positions:

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

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