Creating regex to extract 4 digit number from string using java

Question

Hi I am trying to build one regex to extract 4 digit number from given string using java. I tried it in following ways:

String mydata = "get the 0025 data from string";
    Pattern pattern = Pattern.compile("^[0-9]+$");
    //Pattern pattern = Pattern.compile("^[0-90-90-90-9]+$");
    //Pattern pattern = Pattern.compile("^[\\d]+$");
    //Pattern pattern = Pattern.compile("^[\\d\\d\\d\\d]+$");

    Matcher matcher = pattern.matcher(mydata);
    String val = "";
    if (matcher.find()) {
        System.out.println(matcher.group(1));

        val = matcher.group(1);
    }

But it's not working properly. How to do this. Need some help. Thank you.

Solution 1

Change you pattern to:

Pattern pattern = Pattern.compile("(\\d{4})");

\d is for a digit and the number in {} is the number of digits you want to have.

Solution 2

If you want to end up with 0025,

String mydata = "get the 0025 data from string";
mydata = mydata.replaceAll("\\D", ""); // Replace all non-digits

Solution 3

Pattern pattern = Pattern.compile("\\b[0-9]+\\b");

This should do it for you.^$ will compare with the whole string.It will match string with only numbers.

Comments

[Sarz]

Try something like are you not sure about it?

[Chop]

Would it not be better to drop the parentheses and use group(0)? (micro-optimization, true, but when dealing with more complex patterns, it could come in handy)

[JiriS]

Okay - corrected (The original question used as well expression "...I tried it in following ways:...")

[Noor Hossain]

this is the best and easiest approach.