How to remove leading zeros from numeric text?

Question

I am using this to remove leading zeros from my input string.

return a.replaceAll("^0+",""); 

But the above string even removes from any string which is alphanumeric as well. I do not want to do that. My requirement is:

Only the leading zeros of numeric numbers should be removed e.g.

00002827393 -> 2827393

If you have a alpha numeric number the leading zeros must not be removed e.g.

000ZZ12340 -> 000ZZ12340

Answer 1

You can check if your string is only composed of digits first :

Pattern p = Pattern.compile("^\\d+$");
Matcher m = p.matcher(a);

if(m.matches()){
  return a.replaceAll("^0+", "");
} else {
  return a;
}

Also :

• consider making your pattern static, that way it will only be created once
• you may want to isolate the part with the matcher in a smaller function, "isOnlyDigit" for example

Answer 2

You can also try this:

a.replaceAll("^0+(?=\\d+$)", "")

Notice that the positive lookahead (?=\\d+$) checks to see that the rest of the string (after the starting 0s, matched by ^0+) is composed of only digits before matching/replacing anything.

---

System.out.println("00002827393".replaceAll("^0+(?=\\d+$)", ""));
System.out.println("000ZZ12340".replaceAll("^0+(?=\\d+$)", ""));

2827393
000ZZ12340

Answer 3

Test if the incoming string matches the numeric pattern "\d+". "\d" is the character class for digits. If it's numeric, then return the result of the call to replaceAll, else just return the original string.

if (str.matches("\\d+"))
    return str.replaceAll("^0+", "");
return str;

Testing:

public static void main (String[] args) throws java.lang.Exception
{
   System.out.println(replaceNumZeroes("0002827393"));
   System.out.println(replaceNumZeroes("000ZZ1234566"));
}

yields the output

2827393
000ZZ1234566