Java：如何根据非字母分隔符反转字符串？

Question

如何根据非字母分隔符反转字符串？我怀疑我的正则表达式可能是问题所在。

String fileContent = "Joe'); MAKE TEST random;--";
String[] splitWords = fileContent.split("[^a-zA-Z0-9']+");

StringBuilder stringBuilder = new StringBuilder();
for (String word : splitWords) {
    int idx = fileContent.indexOf(word, stringBuilder.length());
    String delim = fileContent.substring(stringBuilder.length(), idx);
    stringBuilder.append(delim);

    StringBuilder output = new StringBuilder(word).reverse();
    stringBuilder.append(output);
}
return stringBuilder.toString();

当前输出：'eoJ); EKAM TSET modnar

所需输出：eoJ'); EKAM TSET modnar;--

Answer 1

您不需要正则表达式。您似乎想要反转仅是字母或数字的字符。 然后你可以这样做 - 获取字符数组的开始和结束索引，你发现字符是字母或数字，然后就地反转。然后返回一个字符反转的新字符串。

private static void reverseWords(char[] c) {
    int start = 0, end = c.length;
    while ( start < end ) {
      int pre = start;
      while ( start < c.length && Character.isLetterOrDigit(c[start]) ) 
        start++;
      if ( pre < start ) 
         reverseWord(c, pre, start-1);
      start++;  
    }
  }

  private static void reverseWord(char[] c, int start, int end) {
    while ( start < end ) {
      char temp = c[start];
      c[start] = c[end];
       c[end]  = temp;
      start++;
      end--;
    }
  }

你可以测试这段代码here

Answer 2

您可以只匹配和反转 1+ 个字母的块（使用简单的\p{L}+ 模式），其余部分保持原样：

String s = "Joe'); MAKE TEST random;--";
StringBuffer result = new StringBuffer();
Matcher m = Pattern.compile("\\p{L}+").matcher(s);
while (m.find()) {
    String replacement = new StringBuilder(m.group()).reverse().toString();
    m.appendReplacement(result, replacement);
}
m.appendTail(result);
System.out.println(result.toString()); // => eoJ'); EKAM TSET modnar;--

请参阅Java demo online。

Answer 3

您的代码有两个变化：

1. 替换模式
2. 测试尾随分隔符

String fileContent = "Joe'); MAKE TEST random;--"; String[] splitWords = fileContent.split("\W"); // W 是非单词字符或 我忘记了

StringBuilder stringBuilder = new StringBuilder();
for (String word : splitWords) {
    int idx = fileContent.indexOf(word, stringBuilder.length());
    String delim = fileContent.substring(stringBuilder.length(), idx);
    stringBuilder.append(delim);

    StringBuilder output = new StringBuilder(word).reverse();
    stringBuilder.append(output);
}
// did we have trailing delimiter ?
if(fileContent.length()!=stringBuilder.length())
{ //append remaining
    stringBuilder.append(fileContent.substring(stringBuilder.length()));
}
return stringBuilder.toString();