bowling-kata/src/main/java/BowlingGameCalculator.java

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

public class BowlingGameCalculator {

    private static final Pattern SINGLE_VALUE_PATTERN = Pattern.compile("\\d");
    private static final Pattern SPARE_PATTERN = Pattern.compile("(\\d)[ ,]*/[ -,]*(\\d)");
    private static final int INITIAL_SCORE_VALUE = 0;

    public int score(String playerResult) {
        int playerScore = INITIAL_SCORE_VALUE;

        playerScore += scoreMatch(SINGLE_VALUE_PATTERN.matcher(playerResult), (spareMatcher) -> Integer.parseInt(spareMatcher.group()));
        playerScore += scoreMatch(SPARE_PATTERN.matcher(playerResult), (spareMatcher) ->
                10 + Integer.parseInt(spareMatcher.group(2))
                        - Integer.parseInt(spareMatcher.group(1)));

        return playerScore;
    }

    private int scoreMatch(Matcher scoreMatch, Function<Matcher, Integer> scorer) {
        int playerScore = INITIAL_SCORE_VALUE;
        while (scoreMatch.find()) {
            playerScore += scorer.apply(scoreMatch);
        }
        return playerScore;
    }
}