java java正则表达式中“\\d+”和“\\d++”的区别
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Difference between "\\d+" and "\\d++" in java regex
提问by user2313900
In java, what's the difference between "\\d+"and "\\d++"?
I know ++ is a possessive quantifier, but what's the difference in matching the numeric string?
What string can match "\\d+"but can't with "\\d++"?
Possessive quantifier seems to be significant with quantifier ".*"only. Is it true?
在java中，什么之间的区别"\\d+"和"\\d++"？我知道 ++ 是一个占有量词，但是匹配数字字符串有什么区别？什么字符串可以匹配"\\d+"但不能匹配"\\d++"？所有格量词似乎".*"仅对量词有意义。这是真的吗？
回答by erickson
Possessive quantifiers will not back off, even if some backing off is required for the overall match.
占有量词不会退让，即使整体匹配需要一些退让。
So, for example, the regex \d++0can never match any input, because \d++will match all digits, including the 0needed to match the last symbol of the regex.
因此，例如，正则表达式\d++0永远无法匹配任何输入，因为\d++它将匹配所有数字，包括0匹配正则表达式最后一个符号所需的数字。
回答by Sumit Singh
\d+ Means:\dmeans a digit (Character in the range 0-9), and +means 1 or more times. So, \d+is 1 or more digits.
\d+\d表示：表示一个数字（0-9范围内的字符），+表示1次或多次。所以，\d+是 1 位或更多位数字。
\d++ Meansfrom Quantifiers
\d++来自量词的均值
This is called the possessive quantifiers and they always eat the entire input string, trying once (and only once) for a match. Unlike the greedy quantifiers, possessive quantifiers never back off, even if doing so would allow the overall match to succeed.
这称为所有格量词，它们总是吃掉整个输入字符串，尝试一次（且仅一次）匹配。与贪婪量词不同，所有格量词永远不会退缩，即使这样做会使整体匹配成功。
