Java Integer To Fixed Length String Examples

Mar 29, 2015 Core Java, Examples, Snippet, String comments

There are cases when we need to Convert a Java Integer To Fixed Length String. The logic should append a certain character, usually blank or zero, to fill the missing characters when the number of digits is less than the required number of characters.

Why Fixed Length String?

Sometimes it is important to guarantee width. Like when we wish to display tabular data on a simple text file. E.g.

Unit Price   Quantity   Total Price
      1.50       1000          1500
     12.25        100          1225
      3.10         10            31

This is easy to achieve when we format each column with a fix length. E.g. Format unit price column using 10 characters, format quantity column using 8 characters, etc.

Pad Using StringBuilder

The simplest way to solve this problem is to code the logic ourselves. We can use a StringBuilder to pad the prefix and append the number last. Below is an example using the character zero (0) to pad the number.

public class Test {
   public static void main(String[] args) {
      int number = 15;
      String numberAsString = String.valueOf(number);
      StringBuilder sb = new StringBuilder();
      while(sb.length()+numberAsString.length()<10) {
         sb.append('0');
      }
      sb.append(number);
      String paddedNumberAsString = sb.toString();
      System.out.println(paddedNumberAsString);
   }
}

The code formats the String to 10 characters long.

Here is the sample output.

0000000015

Pad Using Substring Trick

Here is a simple trick that uses substring to determine the String to pad the number. Here is an example that shows 3 different numbers to show that the logic works.

public class Test {
   public static void main(String[] args) {
      // 1 digit
      int number = 1;
      String numberAsString = String.valueOf(number);
      String paddedNumberAsString = "0000000000".substring(numberAsString.length()) + numberAsString;
      System.out.println(paddedNumberAsString);
      // 2 digits
      number = 12;
      numberAsString = String.valueOf(number);
      paddedNumberAsString = "0000000000".substring(numberAsString.length()) + numberAsString;
      System.out.println(paddedNumberAsString);   
      // 3 digits
      number = 125;
      numberAsString = String.valueOf(number);
      paddedNumberAsString = "0000000000".substring(numberAsString.length()) + numberAsString;
      System.out.println(paddedNumberAsString);   
   }
}

Here is the sample output

0000000001
0000000012
0000000125

Pad Using String.format()

If you are using Java 5 and above, you may use the static method String.format() to achieve the desires result. Here is an example that converts and integer to fixed length String. The result should have 10 characters. The number zero(0) will be used as padding.

public class Test {
   public static void main(String[] args) {
      int number = 153;
      String numberAsString = String.format("%010d", number);
      System.out.println(numberAsString);
   }
}

Here is the output:

0000000153

Here is a modified code that uses space instead of zero to pad the resulting String.

public class Test {
   public static void main(String[] args) {
      int number = 153;
      String numberAsString = String.format("% 10d", number);
      System.out.println(numberAsString);
   }
}

Here is the output:

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