java - 正则表达式，试图匹配不超过一个句点？

Question

使用:http://www.regexplanet.com/advanced/java/index.html

并测试正则表达式:

\.{0,1} 

(?=.*?\.{0,1})

我指的是这个:http://www.rexegg.com/regex-lookarounds.html ，并尝试其他组合，但没有任何效果符合我的要求。

例如，对于测试输入和匹配，我期望..

lo.cat.tion - no match
location - match
loc_ation - match
loc.ation - match

但它告诉我根本没有匹配项。我在这里做错了什么？ :(

Answer 1

一种在整个输入中只匹配一个点或不匹配点的简单方法如下:

String[] input = {
                "lo.cat.tion", // - no match
                "location", // - match
                "loc_ation", // - match
                "loc.ation" // - match
        };
//                           | start of input
//                           || non dots, 0 or more
//                           ||    | 1 dot or nothing (dot requires \\escaping here)
//                           ||    |   | non dots, 0 or more
//                           ||    |   |    | end of input
Pattern p = Pattern.compile("^[^.]*\\.?[^.]*$");
for (String s: input) {
    Matcher m = p.matcher(s);
    // we use "matches" instead of "find", to match the entire input here, 
    // although in this context both methods yield equivalent results
    System.out.printf("Matches for \"%s\"? %b%n", s, m.matches());
}

输出

Matches for "lo.cat.tion"? false
Matches for "location"? true
Matches for "loc_ation"? true
Matches for "loc.ation"? true