Regex for finding dates in a string

Question

Hello people thanks for the help so far. I Have a regex for finding a date in a given string and it does not seem to working. Could someone tell me what I am doing wrong? The code goes something like

Pattern pattern = Pattern.compile("^(0[1-9]|[12][0-9]|3[01])[- /.](0[1-9]|1[012])[- /.](19|20)\\d\\d(?:,)$");
Matcher match = pattern.matcher(text1);

List<String> removable1 = new ArrayList<String>();             
while(match.find()) {
    removable1.add(match.group());
}

I know that there is a date "7/2/2013" contained in the string text1 which is not being written to the list removable1. Any help is appreciated thanks in advance.

Answer 1

Your pattern does not allow for single-digit days and months. Make the leading 0 optional:

^(0?[1-9]|[12][0-9]|3[01])[- /.](0?[1-9]|1[012])[- /.](19|20)\\d\\d(?:,)$

Also, I'm not sure what the trailing comma does. And additionally, you say "contained in the string", but ^ and $ anchor the pattern to the start and end. So you might want to remove these, if you want to find dates:

(0?[1-9]|[12][0-9]|3[01])[- /.](0?[1-9]|1[012])[- /.](19|20)\\d\\d

Finally, if you want to make sure that both date separators are the same character, you can do this:

(0?[1-9]|[12][0-9]|3[01])([- /.])(0?[1-9]|1[012])\\2(19|20)\\d\\d

Finally, for some optimization, avoid capturing where you don't need it (and potentially make the century optional:

(?:0?[1-9]|[12][0-9]|3[01])([- /.])(?:0?[1-9]|1[012])\\1(?:19|20)?\\d\\d

Answer 2

Try this

String text1="07/02/2013";
Pattern pattern = Pattern.compile("^(0[1-9]|[12][0-9]|3[01])[- /.](0[1-9]|1[012])[- /.](19|20)\\d\\d$");

Answer 3

regex you used is not correct. Task section to match day for example

0[1-9]|[12][0-9]|3[01])

This regex means 0 should be used as prefix if day is 1~9.

To fix this issue , you should add ? which means preceding item is optional. So you can change your regex string to

(0?[1-9]|[12][0-9]|3[01])[- /.](0?[1-9]|1[012])[- /.](19|20)\d\d

In future, you can use regular expression tester to debug those issues. They are useful and helps to save time. For example, http://regex.uttool.com , http://regexpal.com/