Development Java Tutorial

The 0 flag causes output to be padded with zeros rather than spaces.
The 0 flag can be used with all format specifiers except %n.

import java.util.Formatter;
public class MainClass {
  public static void main(String args[]) {
    Formatter fmt = new Formatter();
    fmt.format("%05d", 100);
    System.out.println(fmt);
  }
}
00100