[英]How to replace only some of the matched substrings?
這是一個我無法找到答案的正則表達式問題:
輸入:
"the current time is <start time>00:00:00<end time>. at 00:00:00 there is a firework. Another appearance of 00:00:00."
期望的輸出:
"the current time is <start time>00:00:00<end time>. at <start time>00:00:00<end time> there is a firework. Another appearance of <start time>00:00:00<end time>."
解決方案不得涉及首先按句子拆分字符串。
我嘗試了什么:
一個簡單的input.replace(group, replace)
將不起作用,因為已經有一個不應該被替換的匹配。
public static void main(String[] args) throws ParseException
{
String input = "the current time is <start time>00:00:00<end time>. at 00:00:00 there is a firework. Another appearance of 00:00:00.";
Pattern p = Pattern.compile("(<start time>)?(00:00:00)(<end time>)?");
Matcher m = p.matcher(input);
while(m.find())
{
if(m.group(1) != null) { continue; }
String substr1 = input.substring(0, m.start(2));
String substr2 = input.substring(m.end(2), input.length());
String repl = "<start time>" + m.group(2) + "<end time>";
input = substr1 + repl + substr2;
}
}
您的代碼無法正常工作的原因是您正在修改循環內的input
,使匹配結果上的索引無效。
但好消息是你根本不需要循環,你可以使用負向lookbehind和負向前瞻( 這里的詳細信息 )的組合來跳過已經自動包裝的實例,並使用replaceAll
來執行循環為了你:
public static void main(String[] args) throws Exception
{
String input = "the current time is <start time>00:00:00<end time>. at 00:00:00 there is a firework. Another appearance of 00:00:00.";
String result = input.replaceAll("(?<!<start time>)00:00:00(?!<end time>)", "<start time>00:00:00<end time>");
// Negative lookbehind -----------^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^
// Negative lookahead ------------------------------------/
System.out.println(result);
}
負面的背后說“如果文字在它前面就不匹配”,否定的前瞻說“如果文字在它之后就不匹配”。
Lookahead和lookbehind斷言可以幫助你。
負面觀察 : "(?<!start)text"
匹配"footext"
但不匹配"starttext"
,
否定前瞻 : "text(?!end)"
匹配"textfoo"
但不匹配"textend"
。
將此應用於您的案例會導致: "(?<!<start time>)(00:00:00)(?!<end time>)"
。
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