How do I add left-padded zeros to a number in Java? [duplicate]

You can also use the class DecimalFormat, like so:

NumberFormat formatter = new DecimalFormat("00000000"); System.out.println(formatter.format(100)); // 00000100 

Yet another way. ;)

int x = ... String text = (""+(500000000 + x)).substring(1); 

-1 => 99999999 (nines complement)

import java.util.concurrent.Callable; /* Prints. String.format("%08d"): Time per call 3822 (""+(500000000+x)).substring(1): Time per call 593 Space holder: Time per call 730 */ public class StringTimer { public static void time(String description, Callable<String> test) { try { // warmup for(int i=0;i<10*1000;i++) test.call(); long start = System.nanoTime(); for(int i=0;i<100*1000;i++) test.call(); long time = System.nanoTime() - start; System.out.printf("%s: Time per call %d%n", description, time/100/1000); } catch (Exception e) { System.out.println(description+" failed"); e.printStackTrace(); } } public static void main(String... args) { time("String.format(\"%08d\")", new Callable<String>() { int i =0; public String call() throws Exception { return String.format("%08d", i++); } }); time("(\"\"+(500000000+x)).substring(1)", new Callable<String>() { int i =0; public String call() throws Exception { return (""+(500000000+(i++))).substring(1); } }); time("Space holder", new Callable<String>() { int i =0; public String call() throws Exception { String spaceHolder = "00000000"; String intString = String.valueOf(i++); return spaceHolder.substring(intString.length()).concat(intString); } }); } } 

String.format uses a format string which is described here

If you just need to print it out, this is a shorter version:

System.out.printf("%08d\n", number); 

If Google Guava is an Option:

String output = Strings.padStart("" + 100, 8, '0'); 

Alternatively Apache Commons Lang:

String output = StringUtils.leftPad("" + 100, 8, "0"); 

This also works:

int i = 53; String spaceHolder = "00000000"; String intString = String.valueOf(i); String string = spaceHolder.substring(intString.lenght()).contract(intString); 

But the other examples are much easier.

If you need to parse this string and or support i18n consider extending the

java.text.Format 

object. Use the other answers to help you get the format.