Why use named groups only to never use any of them later on in the code?
This rule raises issues every time named groups are:
- defined but never called anywhere in the code through their name;
- defined but called elsewhere in the code by their number instead;
- referenced while not defined.
Noncompliant code example
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
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:
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);
}
