<P>这个是我的类里的一个方法</P> <P>目的是利用正则表达式获得字符串中重复出现的词。</P> <P>public static ArrayList GetRepeatString(string input)<BR>{<BR>&nbsp;&nbsp;&nbsp; ArrayList myList = new ArrayList();<BR>&nbsp;&nbsp;&nbsp; System.Text.RegularExpressions.MatchCollection matches = System.Text.RegularExpressions.Regex.Matches(input, @"\b(?&lt;word&gt;\w+)\s+(\k&lt;word&gt;)\b", System.Text.RegularExpressions.RegexOptions.Compiled | System.Text.RegularExpressions.RegexOptions.IgnoreCase);<BR>&nbsp;&nbsp;&nbsp; if (matches.Count != 0)<BR>&nbsp;&nbsp;&nbsp; {<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; foreach (Match match in matches)<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; {<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; myList.Add(match.Groups["word"].Value);<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; }<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; return myList;<BR>&nbsp;&nbsp;&nbsp; }<BR>&nbsp;&nbsp;&nbsp; else<BR>&nbsp;&nbsp;&nbsp; {<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; return myList = null;<BR>&nbsp;&nbsp;&nbsp; }<BR>}<BR>输入的字符串明明有重复字符，却matches.Count=0，为什么啊？<BR></P>