Prepend zeros to int java

Question

I want to prepend zeros to an int if its string equivalent length is less than 6. Similar to String.format. Example:

int e = 21;
System.out.println(String.format("%06d", e)); //000021
int e = 3564;
System.out.println(String.format("%06d", e)); //003564

What I need is for the above inputs 210000 and 356400 the zeros prepended at the end. Is there something already implemented which will do the job or do i need to code it by my self? If so how to deal with variable length?

Use padding. http://commons.apache.org/proper/commons-lang/javadocs/api-2.6/org/apache/commons/lang/StringUtils.html#rightPad(java.lang.String,%20int,%20char) — Abhijith Nagarajan, May 08 '19 at 15:35
Also, you don't have to call `String.format()`. You can use `System.out.printf()` when printing formatted values. — WJS, May 08 '19 at 15:52

Silviu Burcea · Accepted Answer · 2019-05-08T15:40:33.717

4

while (e < 100_000) e *= 10;

Self-explanatory. I don't think there is an easier way than that.

Edit: Since e can be 0, I'd wrap the above statement into a function:

public static String pad(int input) {
  if (input == 0) return "000000";
  while (input < 100_000) input *= 10;
  return "" + input;
}

edited May 08 '19 at 15:40

answered May 08 '19 at 15:32

Silviu Burcea

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3

What do you do if `e` is `0`? :) – ROMANIA_engineer May 08 '19 at 15:36
1

Thank you very much. This easy solution haven't come to my mind. Will accept the answer when the ten minutes are over. – Trillian May 08 '19 at 15:38
@ROMANIA_engineer edited to handle 0 as well. – Silviu Burcea May 08 '19 at 15:40
@ROMANIA_engineer good point but irrelevant for my context as my inputs are always > 0. – Trillian May 08 '19 at 15:41
@SilviuBurcea it also doesn't handle negative numbers. – Andy Turner May 08 '19 at 15:44
@AndyTurner I know, but I assumed that negative numbers are not valid for the problem that's being solved. I only focused to provide a working solution for OP's problem, not handle every possible case. One would be able to derive a solution for negative numbers having my answer's root idea, if that is needed. – Silviu Burcea May 08 '19 at 16:03
@SilviuBurcea one would have been able to derive how to handle zero too :) – Andy Turner May 08 '19 at 16:10

Andy Turner · Answer 2 · 2019-05-08T15:59:10.170

4

If wanted to do something like what Dimitri suggests, but you don't want to depend on an external library, you write a little method:

StringBuilder sb = new StringBuilder(6);
sb.append(e);
sb.append("000000", Math.min(sb.length(), 6), 6);
return sb.toString();

edited May 08 '19 at 15:59

answered May 08 '19 at 15:40

Andy Turner

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score 1 · Answer 3 · answered May 08 '19 at 15:35

1

If you can use StringUtils, you have access to the rightPad method :

StringUtils.rightPad(String.valueOf(e), 6, "0");

answered May 08 '19 at 15:35

Dimitri Mockelyn

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Note: That is a third party class. Not part of the Java API. – WJS May 08 '19 at 15:55

WJS · Answer 4 · 2019-05-08T16:07:32.947

The following method pads the supplied string, with the supplied character, until the field width is reached.

   public static String rightPad(String str, int fieldwidth, char c) {
      StringBuilder sb = new StringBuilder(str);
      while (fieldwidth > sb.length()) {
         sb.append(c);
      }
      return sb.toString();
   }

Example: To pad 1234 with two zeros, do the following:

int v = 1234;
String padded = rightPad(Integer.toString(v), 6, '0');

Prepend zeros to int java

4 Answers4