キャメルケース→スネークケース変換処理を、正規表現、Stringの結合、StringBuilderで比較

Main.java

// キャメルケース→スネークケース変換処理
public class Main {
    public static void main(String[] args) throws Exception {
        
        String target = "snicMakinoTestCase";
        System.out.println("テストケース：" + target + "\n");
        
        Main main = new Main();
            
        main.timeMeasure(
            "正規表現",
            target,
            (str) -> {
                return str.replaceAll("([A-Z])", "_$1").toLowerCase();
            });

        main.timeMeasure(
            "くるくる",
            target,
            (str) -> {
                String result = "";
                for (char c : str.toCharArray()) {
                    if (Character.isUpperCase(c)) {
                        result += "_" + Character.toString(Character.toLowerCase(c));
                        continue;
                    }
                    result += Character.toString(c);
                }
                return result;
            });

        main.timeMeasure(
            "くるくる２",
            target,
            (str) -> {
                StringBuilder result = new StringBuilder();
                for (char c : str.toCharArray()) {
                    if (Character.isUpperCase(c)) {
                        result.append('_').append(Character.toLowerCase(c));
                        continue;
                    }
                    result.append(c);
                }
                return result.toString();
            });
        
    }

    public void timeMeasure(String name, String target, CamelToSnake camelToSnake) {
        System.out.println("処理名：" + name);
        System.out.println("処理結果：" + camelToSnake.execute(target));

        long start = System.currentTimeMillis();

        for (int i = 0; i < 10000; i++) {
            camelToSnake.execute(target);
        }

        long end = System.currentTimeMillis();

        System.out.printf("実行時間：%d\n\n", end - start);
    }

    public interface CamelToSnake {
        public String execute(String arg);
    }
}