== Why is this an issue?

include::../description.adoc[]

=== Noncompliant code example

[source,java]
----
String date = "01/02";

Pattern datePattern = Pattern.compile("(?<month>[0-9]{2})/(?<year>[0-9]{2})"); 
Matcher dateMatcher = datePattern.matcher(date);

if (dateMatcher.matches()) {
  checkValidity(dateMatcher.group(1), dateMatcher.group(2));  // Noncompliant - numbers instead of names of groups are used
  checkValidity(dateMatcher.group("day")); // Noncompliant - there is no group called "day"
}

// ...

String score = "14:1";

Pattern scorePattern = Pattern.compile("(?<player1>[0-9]+):(?<player2>[0-9]+)"); // Noncompliant - named groups are never used
Matcher scoreMatcher = scorePattern.matcher(score);

if (scoreMatcher.matches()) {
  checkScore(score);
}
----


=== Compliant solution

[source,java]
----
String date = "01/02";

Pattern datePattern = Pattern.compile("(?<month>[0-9]{2})/(?<year>[0-9]{2})");
Matcher dateMatcher = datePattern.matcher(date);

if (dateMatcher.matches()) {
  checkValidity(dateMatcher.group("month"), dateMatcher.group("year"));
}

// ...

String score = "14:1";

Pattern scorePattern = Pattern.compile("(?<player1>[0-9]+):(?<player2>[0-9]+)");
Matcher scoreMatcher = scorePattern.matcher(score);

if (scoreMatcher.matches()) {
  checkScore(scoreMatcher.group("player1"));
  checkScore(scoreMatcher.group("player2"));
}
----
Or, using dedicated variables instead of group names:

[source,java]
----
String score = "14:1";

String player = "([0-9]+)";
String gameScore = player + ":" + player;

Pattern scorePattern = Pattern.compile(gameScore);
Matcher scoreMatcher = scorePattern.matcher(score);

if (scoreMatcher.matches()) {
  checkScore(score);
}
----

ifdef::env-github,rspecator-view[]

'''
== Implementation Specification
(visible only on this page)

include::message.adoc[]

include::highlighting.adoc[]

endif::env-github,rspecator-view[]
