Adding 0's to string/int variable

Question

So I have been working on a naming convention which add 0's before a string. I'm trying to do this the short handed way before breaking everything into if statements. Here I print 0's before an int giving me an answer of 00005.

String test = null;
int n = 5;
test = String.format("%05d%n", n);  
System.out.println(test);

Now what I would like to do is do this to a String. So for example if String n = "5"; it would give me an answer of 00005 and if String n = "20"; it would be 00020. I do not wish to use the integer method to change the string to and int, and back into a string. Any help would be appreciated. Thank you!

Answer 1

Assuming that n is a String that represents a number, or more generally that n doesn't have any space characters:

String.format("%5s",n).replace(" ","0");

Answer 2

Not sure if it's the best way, but that's what I use.

public static String pad (String input, char with, int desiredLength)
{
    if (input.length() >= desiredLength) {
        return input;
    }
    StringBuilder output = new StringBuilder (desiredLength);
    for (int i = input.length (); i < desiredLength; i++) {
        output.append (with);
    }
    output.append (input);

    return output.toString();
}

Usage (assuming the static method is in a class called Utils) :

System.out.println (Utils.pad(myString,'0',10));

EDIT : generalized to any input String, character to pad with, and desired output length.

Answer 3

How about this?

("00000" + numberAsString).substring(numberAsString.length())

This will only work if you have 5 or less digit numbers.

Ideone link to check code

Reference

To be honest, I also think 4 times how this code works, but after understanding I posted as this is something out of the box.