`Greedy`和`Reluctant`正则表达式量词有什么区别？ [英] What is the difference between `Greedy` and `Reluctant` regular expression quantifiers?

问题描述

来自 模式 javadocs：

From the Pattern javadocs:

Greedy quantifiers:
X?      X, once or not at all  
X*      X, zero or more times  
X+      X, one or more times  
X{n}    X, exactly n times  
X{n,}   X, at least n times  
X{n,m}  X, at least n but not more than m times

Reluctant quantifiers:
X??     X, once or not at all  
X*?     X, zero or more times  
X+?     X, one or more times  
X{n}?   X, exactly n times  
X{n,}?  X, at least n times  
X{n,m}? X, at least n but not more than m times

他们所做的描述是相同的...那么，什么是差异？

The description of what they do is the same...so, what is the difference?

我真的很感激一些例子。

I would really appreciate some examples.

我用Java编码，但我听到这个概念对于大多数现代正则表达式实现都是一样的。

推荐答案

贪婪的运营商总是试图抓住尽可能多的输入，而不情愿的量词将尽可能少地匹配输入并仍然创建匹配。

A greedy operator always try to "grab" as much of the input as possible, while a reluctant quantifier will match as little of the input as possible and still create a match.

示例：

"The red fox jumped over the red fence"
/(.*)red/ => \1 = "The red fox jumped over the "
/(.*?)red/ => \1 = "The "

"aaa"
/a?a*/ => \1 = "a", \2 = "aa"
/a??a*/ => \1 = "", \2 = "aaa"

"Mr. Doe, John"
/^(?:Mrs?.)?.*\b(.*)$/ => \1 = "John"
/^(?:Mrs?.)?.*?\b(.*)$/ => \1 = "Doe, John"

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