java - 正则表达式 - 无法将西里尔字母与\w匹配

Question

任务:

The task must be solved using regular expressions without using container classes.

Input: text (may consist of Latin and Cyrillic). Output: source text, but the case of the first character of each word, which consists of three or more characters, must be inverted.

To consider a word as a sequence containing only letters (all other characters are not included in the word). Create a static convert method that converts input to output.

Example Input data

When I was younger
I never needed
Прощай, со всех вокзалов поезда
уходят в Дальние Края

Example Output

when I Was Younger
I Never Needed
прощай, со Всех Вокзалов Поезда
Уходят в дальние края

我的尝试:

public static String convert(String input) {
    StringBuilder sb = new StringBuilder(input);
    Pattern p = Pattern.compile("[\\W&&[\\d]]?[\\w&&[\\D]]+");
    Matcher m = p.matcher(input);
    while (m.find()) {
        if (m.group().length() >= 3) {
            if (Character.isUpperCase(sb.charAt(m.start()))) {
                sb.setCharAt(m.start(), Character.toLowerCase(sb.charAt(m.start())));
            } else {
                sb.setCharAt(m.start(), Character.toUpperCase(sb.charAt(m.start())));
            }

        }
    }
    return sb.toString();
}

我需要输出:

when I Was Younger
I Never Needed
прощай, со Всех Вокзалов Поезда
Уходят в дальние края

但我有:

when I Was Younger
I Never Needed
Прощай, со всех вокзалов поезда
уходят в Дальние Края

Answer 1

调试问题

\w 与西里尔字符不匹配。我通过在 while 循环中打印匹配的组来解决这个问题:

System.out.println(m.group());

打印:

When
I
was
younger
I
never
needed

没有其他单词匹配。

解决方案1

要匹配西里尔字符，您可以使用 \p{L}。如果您使用 {3} 匹配三个字符，则可以避免在循环中进行长度检查。 \b 匹配边界字符。把它们放在一起:

public static String convert(String input) {
    StringBuilder sb = new StringBuilder(input);
    Pattern p = Pattern.compile("\\b\\p{L}{3}");
    Matcher m = p.matcher(input);
    while (m.find()) {
        char firstChar = sb.charAt(m.start());
        if (Character.isUpperCase(firstChar)) {
            sb.setCharAt(m.start(), Character.toLowerCase(firstChar));
        } else {
            sb.setCharAt(m.start(), Character.toUpperCase(firstChar));
        }
    }
    return sb.toString();
}

产品:

when I Was Younger
I Never Needed
прощай, со Всех Вокзалов Поезда
Уходят в дальние края

解决方案2

或者，如果您想要真正漂亮，请使用正向前瞻(非捕获组)和采用 lambda 的匹配器 replaceAll 方法:

public static String convert(String input) {
    Pattern p = Pattern.compile("\\b(\\p{L})(?=\\p{L}{2})");
    Matcher m = p.matcher(input);
    return m.replaceAll(match -> {
        char ch = match.group().charAt(0);
        if (Character.isUpperCase(ch)) {
            return "" + Character.toLowerCase(ch);
        }
        return "" + Character.toUpperCase(ch);
    });
}

还生产:

when I Was Younger
I Never Needed
прощай, со Всех Вокзалов Поезда
Уходят в дальние края