Java Regex：matches（pattern，value）返回true但group（）无法匹配 [英] Java Regex: matches(pattern, value) returns true but group() fails to match

问题描述

我在Java中使用正则表达式有一个奇怪的问题。我测试了我的正则表达式和我的价值

I have an odd problem with a regular expression in Java. I tested my Regex and my value here and it works. It says there are 3 groups (correct) the match for the first group (not group zero!) is SSS, the match for group 2 is BB and the match for group 3 is 0000. But my code below fails and I am quite at a loss why...

String pattern = "([^-]*)-([\\D]*)([\\d]*)";
String value = "SSS-BB0000";
Matcher matcher = Pattern.compile(pattern).matcher(value);
//group() is equivalent to group(0) - it fails to match though
matcher.group();

Here is a screenshot from the matching result of the above website:

I'd be really grateful if anyone could point out the mistake I am making... On an additional note: Strangely enough, if I execute the following code true is returned which implies a match should be possible...

//returns true
Pattern.matches(pattern, value);

解决方案

You need to call find() before group():

String pattern = "([^-]*)-([\\D]*)([\\d]*)"; 
String value = "SSS-BB0000";
Matcher matcher = Pattern.compile(pattern).matcher(value); 
if (matcher.find()) {
  System.out.println(matcher.group()); // SSS-BB0000
  System.out.println(matcher.group(0)); // SSS-BB0000
  System.out.println(matcher.group(1)); // SSS
  System.out.println(matcher.group(2)); // BB
  System.out.println(matcher.group(3)); // 0000
}

When you invoke matcher(value), you are merely creating a Matcher object that will be able to match your value. In order to actually scan the input, you need to use find() or lookingAt():

References:

• Matcher#find()

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