我的正则表达式有什么问题 - ？\\\\ d {2} \\\\。？\\\\ d {6}

Question

I'm trying extract lat and long from a url:

source:
...sensor=false&center=-15.842208999999999%2C-48.023084&zoom=17&size=256x256&language=en&client=google-maps-frontend&signature=hbey3U4lycTNgX48asW8MODjJLM

I'm not good in regexes, so I used this regex tester ( http://regexpal.com/ ) and coded this regex

-?\d{2}\.?\d{6}

(is for JAVA )

It produces this result (who's saying it is regexpal.com):

for (Element element : newsHeadlines) {
        if(element.toString().contains("https://maps.google.com")){
            List<String> lista = get_matches(element.attr("content"), "-?\\d{2}\\.?\\d{6}");


        }
    }

public static List<String> get_matches(String s, String p) {
    // returns all matches of p in s for first group in regular expression 
    List<String> matches = new ArrayList<String>();
    Matcher m = Pattern.compile(p).matcher(s);
    while(m.find()) { 
        matches.add(m.group(1)); //<-- Exception m.group(1) not have any results.
    }
    return matches;
}

So when I do it (in java):

 for (Element element : newsHeadlines) { if(element.toString().contains("https://maps.google.com")){ List<String> lista = get_matches(element.attr("content"), "-?\\\\d{2}\\\\.?\\\\d{6}"); } } public static List<String> get_matches(String s, String p) { // returns all matches of p in s for first group in regular expression List<String> matches = new ArrayList<String>(); Matcher m = Pattern.compile(p).matcher(s); while(m.find()) { matches.add(m.group(1)); //<-- Exception m.group(1) not have any results. } return matches; } 

What's wrong with my regex?

Answer 1

Your method get_matches is looking for m.group(1) groups are defined in Regex with Parenthesis. So you regex needs to be like this instead:

(-?\\d{2}\\.?\\d{6})

Online Demo

Answer 2

Just make one symbol as optional whether it may be - or . .

-\d{2}\.?\d{6}

Equivalent java regex:

-\\d{2}\\.?\\d{6}

OR

-?\d{2}\.\d{6}

Equivalent java regex:

-?\\d{2}\\.\\d{6}

DEMO

And call m.group(0) to print only the matched strings. If you want to call m.group(1) then you need to enclose the patterns within paranthesis.