Specific Java Regex For Set Notation

Question

I'm trying to write a regex expression that will check that a string is in the formation of a Set of integers

ex: {1, 23, -501, 52, 2387329, 0}

So far I've got:

Pattern p = [({(([0-9]+,)*[0-9]+)})]

But it doesn't seem to be working... Can anyone help me out?

Thanks!

You don't handle `-` sign?? Can you show some examples of strings that work and don't work? — Floris, Mar 24 '13 at 03:33
One useful technique as you develop complex regular expressions is to build them up from named Strings. `String lbrace = "[{]";` and `String sInteger = "[+-]?\\d+";`. Then build up your pattern from these. Look at the mail pattern in the second edition of Mastering Regular Expressions. — Eric Jablow, Mar 24 '13 at 03:44
I'm very new to regex and am not really sure what I'm doing here. Some examples that work would be: {1, 2, 3} {} {3} and those that don't work are: {1 2 3} {a, b, c} — user1217119, Mar 24 '13 at 03:53
No. They should be numbers separated by commas. I can always take the spaces out by formatting the string, so even the spaces aren't necessary — user1217119, Mar 24 '13 at 03:58

score 1 · Answer 1 · answered Mar 24 '13 at 03:31

Pattern.compile("\\{\\s*(?:\\d+(?:\\s*,\\s*\\d+\\s*)*)?\\}")

matches curly brackets surrounding zero or more comma-separated non-negative decimal integers.

\\s matches any space character. The (?:...) are just for grouping, and the stuff between the curly brackets is effectively (decimal digits followed by (any number of commas then decimal digits)) optionally.

I don't know what notation you're using for

[({(([0-9]+,)*[0-9]+)})]

but it will definitely not match the empty set and won't match anything with spaces after a comma.

score 0 · Answer 2 · answered Mar 24 '13 at 03:53

0

try this regex

"\\{((-?\\d+), ?)*-?\\d+}"

answered Mar 24 '13 at 03:53

Evgeniy Dorofeev

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For some reason {1 2 3} is working with it. Is there any reason why that would be happening? – user1217119 Mar 24 '13 at 04:08
I tested "{1 2 3}".matches("\\{((-?\\d+), )*-?\\d+}"); it returns false – Evgeniy Dorofeev Mar 24 '13 at 04:18

score 0 · Answer 3 · answered Mar 24 '13 at 04:56

Try this out.

        String data = "{1, 23, -501, 52, 2387329, 0}";
    Pattern pattern = Pattern.compile("\\{(\\s?-?\\d+?\\,?\\s?)+?\\}");

    Matcher matcher = pattern.matcher(data);
    while (matcher.find()) {
        // Indicates match is found. Do further processing
        System.out.println(matcher.group());
    }

Specific Java Regex For Set Notation

3 Answers3