为什么Java正则表达式“匹配” vs“找到”使用非贪婪模式时获得不同的匹配？ [英] Why does Java regex "matches" vs "find" get a different match when using non-greedy pattern?

问题描述

所以我遇到了一个错误，因为期望match（）方法找到与使用find（）完全相同的匹配。通常情况就是如此，但看起来如果非贪婪的模式可以被拉伸以贪婪地接受整个字符串，那么它是允许的。这似乎是Java中的一个错误。我错了吗？我没有在文档中看到任何表明此行为的内容。

So I ran into a bug caused by expecting the matches() method to find exactly the same match as using find(). Normally this is the case, but it appears that if a non-greedy pattern can be stretched to greedily accept the whole string, its allowed. This seems like a bug in Java. Am I wrong? I don't see anything in the docs which indicates this behavior.

Pattern stringPattern = Pattern.compile("'.*?'");
String nonSingleString = "'START'===stageType?'active':''";
Matcher m1 = stringPattern.matcher(nonSingleString);
boolean matchesCompleteString = m1.matches();
System.out.println("Matches complete string? " + matchesCompleteString);
System.out.println("What was the match? " + m1.group()); //group() gets the string that matched

Matcher m2 = stringPattern.matcher(nonSingleString);
boolean foundMatch = m2.find(); //this looks for the next match
System.out.println("Found a match in at least part of the string? " + foundMatch);
System.out.println("What was the match? " + m2.group());

输出

匹配完整的字符串？ true

比赛是什么？ 'START'=== stageType？'active'：''

在字符串的至少一部分找到匹配项？ true

比赛是什么？ 'START'

Matches complete string? true
What was the match? 'START'===stageType?'active':''
Found a match in at least part of the string? true
What was the match? 'START'

推荐答案

这很有道理。

匹配（...）方法必须尝试使用​​整个字符串，所以即使使用非贪婪模式也是如此。

The matches(...) method must attempt to consume the whole string, so it does, even with a non-greedy pattern.

find（...）方法可能会找到一个子字符串，因此如果找到任何匹配的子字符串，它会在该点处停止。

The find(...) method may find a substring, so it stops at the point if finds any matching substring.

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