java: use regular expression to extract a number in a string

Question

I have a string of format "[232]......." I want to extract the 232 out of the string, I did this

public static int getNumber(String str) {
    Pattern pattern = Pattern.compile("\\[([0-9]+)\\]");
    Matcher matcher = pattern.matcher(str);
    int number = 0;
    while (matcher.find()) {
        number = Integer.parseInt(matcher.group());
    }
    return number;
}

but it doesn't work, I got the following exception:

Exception in thread "main" java.lang.NumberFormatException: For input string: "[232]"

Anyone knows how could I solve this problem, and if there is a more efficient way for me to do this kind of pattern matching in java?

Answer 1

group() without any parameters returns the entire match (equivalent to group(0) ). That includes the square brackets that you've specified in your regex.

To extract the number, pass 1 to return only the first capture group within your regex (the ([0-9]+) ):

number = Integer.parseInt(matcher.group(1));