How to Insert Commas Into a Number WITHIN a String of Other Words

Question

I have a String like the following:

"The answer is 1000"

I want to insert commas into the number 1000 without destroying the rest of the String.

NOTE: I also want to use this for other Strings of differing lengths, so substring(int index) would not be advised for getting the number.

The best way that I can think of is to use a regex command, but I have no idea how.

Thanks in advance!

Answer 1

The following formats all the non-decimal numbers:

public String formatNumbers(String input) {
  Pattern p = Pattern.compile("\\d+");
  Matcher m = p.matcher(input);
  NumberFormat nf = NumberFormat.getInstance();        
  StringBuffer sb = new StringBuffer();
  while(m.find()) {
    String g = m.group();
    m.appendReplacement(sb, nf.format(Double.parseDouble(g)));            
  }
  return m.appendTail(sb).toString();
}

e.g. if you call: formatNumbers("The answer is 1000 1000000")

Result is: "The answer is 1,000 1,000,000"

See: NumberFormat and Matcher.appendReplacement().

Answer 2

modified from Most efficient way to extract all the (natural) numbers from a string:

import java.util.regex.Pattern;
import java.util.regex.Matcher;

public class Example {

private static final String REGEX = "\\d+";

public static void main(String[] args) {
    String input = "dog dog 1342 dog doggie 2321 dogg";
    Pattern p = Pattern.compile(REGEX);
    Matcher m = p.matcher(input); // get a matcher object
    int end = 0;
    String result = "";
    while (m.find()) {
        result = result + input.substring(end, m.start());
        result = result
                + addCommas(
                        input.substring(
                                m.start(), m.end()));
        end = m.end();
    }
    System.out.println(result);
}

private static String addCommas(String s) {
    char[] c = s.toCharArray();
    String result = "";
    for (int i = 0; i < s.length(); i++) {
        if (s.length() % 3 == i % 3)
            result += ",";

        result += c[i];
    }
    return result;
}

}

Answer 3

You could use the regular expression:

[0-9]+

To find contiguous sets of digits, so it would match 1000, or 7500 or 22387234, etc.. You can test this on http://regexpal.com/ This doesn't handle the case of numbers that involve decimal points, BTW.

This isn't a complete, with code answer, but the basic algorithm is as follows:

• You use that pattern to find the index(es) of the match(es) within the string (the index of the characters where the various matches start)
• From each of those indexes, you copy the digits into a temporary string that contains only the digits of the number(s) in the String
• You write a function that starts at the end of the String, and for every 3rd digit (from the end) you insert a comma before it, unless the index of the current character is 0 (which will prevent 300 from being turned into ,300
• Replace the original number in the source string with the comma'ed String, using the replace() method