How to format a Java string with leading zero?

Here is the String, for example:

"Apple"

and I would like to add zero to fill in 8 chars:

"000Apple"

How can I do so?

public class LeadingZerosExample {
    public static void main(String[] args) {
	   int number = 1500;
	
	   // String format below will add leading zeros (the %0 syntax) 
	   // to the number above. 
       // The length of the formatted string will be 7 characters.
	   
	   String formatted = String.format("%07d", number);
	
	   System.out.println("Number with leading zeros: " + formatted);
    }
}

In case you have to do it without the help of a library:

("00000000" + "Apple").substring("Apple".length())

(Works, as long as your String isn't longer than 8 chars.)

 StringUtils.leftPad(yourString, 8, '0');

This is from commons-lang. https://commons.apache.org/proper/commons-lang/apidocs/org/apache/commons/lang3/StringUtils.html#leftPad-java.lang.String-int-char-">See javadoc

This is what he was really asking for I believe:

String.format("%0"+ (8 - "Apple".length() )+"d%s",0 ,"Apple"); 

output:

000Apple

You can use the String.format method as used in another answer to generate a string of 0's,

String.format("%0"+length+"d",0)

This can be applied to your problem by dynamically adjusting the number of leading 0's in a format string:

public String leadingZeros(String s, int length) {
     if (s.length() >= length) return s;
     else return String.format("%0" + (length-s.length()) + "d%s", 0, s);
}

It's still a messy solution, but has the advantage that you can specify the total length of the resulting string using an integer argument.

Using Guava's Strings utility class:

Strings.padStart("Apple", 8, '0');

You can use this:

org.apache.commons.lang.StringUtils.leftPad("Apple", 8, "0")

I've been in a similar situation and I used this; It is quite concise and you don't have to deal with length or another library.

String str = String.format("%8s","Apple");
str = str.replace(' ','0');

Simple and neat. String format returns " Apple" so after replacing space with zeros, it gives the desired result.

String input = "Apple";
StringBuffer buf = new StringBuffer(input);

while (buf.length() < 8) {
  buf.insert(0, '0');
}

String output = buf.toString();

Use Apache Commons StringUtils.leftPad (or look at the code to make your own function).

You can use:

String.format("%08d", "Apple");

It seems to be the simplest method and there is no need of any external library.

In Java:

String zeroes="00000000";
String apple="apple";
    
String result=zeroes.substring(apple.length(),zeroes.length())+apple;

In Scala:

"Apple".foldLeft("00000000"){(ac,e)=>ac.tail+e}

You can also explore a way in Java 8 to do it using streams and reduce (similar to the way I did it with Scala). It's a bit different to all the other solutions and I particularly like it a lot.

public class PaddingLeft {
	public static void main(String[] args) {
		String input = "Apple";
		String result = "00000000" + input;
		int length = result.length();
		result = result.substring(length - 8, length);
		System.out.println(result);
	}
}

You may have to take care of edgecase. This is a generic method.

public class Test {
    public static void main(String[] args){
    	System.out.println(padCharacter("0",8,"hello"));
    }
    public static String padCharacter(String c, int num, String str){
    	for(int i=0;i<=num-str.length()+1;i++){str = c+str;}
    	return str;
    }
}

public static void main(String[] args)
{
    String stringForTest = "Apple";
    int requiredLengthAfterPadding = 8;
    int inputStringLengh = stringForTest.length();
    int diff = requiredLengthAfterPadding - inputStringLengh;
    if (inputStringLengh < requiredLengthAfterPadding)
    {
        stringForTest = new String(new char[diff]).replace("\0", "0")+ stringForTest;
    }
    System.out.println(stringForTest);
}

public static String lpad(String str, int requiredLength, char padChar) {
    if (str.length() > requiredLength) {
        return str;
    } else {
        return new String(new char[requiredLength - str.length()]).replace('\0', padChar) + str;
    }
}

Did anyone tried this pure Java solution (without SpringUtils):

//decimal to hex string 1=> 01, 10=>0A,..
String.format("%1$2s", Integer.toString(1,16) ).replace(" ","0");
//reply to original question, string with leading zeros. 
//first generates a 10 char long string with leading spaces, and then spaces are
//replaced by a zero string. 
String.format("%1$10s", "mystring" ).replace(" ","0");

Unfortunately this solution works only if you do not have blank spaces in a string.

Solution with method String::repeat (Java 11)

String str = "Apple";
String formatted = "0".repeat(8 - str.length()) + str;

If needed change 8 to another number or parameterize it

I like the solution from Pad a String with Zeros

String.format("%1$" + length + "s", inputString).replace(' ', '0');

with length = "8" and inputString = "Apple"

This is fast & works for whatever length.

public static String prefixZeros(String value, int len) {
    char[] t = new char[len];
    int l = value.length();
    int k = len-l;
    for(int i=0;i<k;i++) { t[i]='0'; }
    value.getChars(0, l, t, k);
    return new String(t);
}

Can be faster then Chris Lercher answer when most of in String have exacly 8 char

int length = in.length();
return length == 8 ? in : ("00000000" + in).substring(length);

in my case on my machine 1/8 faster.

Here is the simple API-less "readable script" version I use for pre-padding a string. (Simple, Readable, and Adjustable).

while(str.length() < desired_length)
  str = '0'+str;

If you want to write the program in pure Java you can follow the below method or there are many String Utils to help you better with more advanced features.

Using a simple static method you can achieve this as below.

public static String addLeadingText(int length, String pad, String value) {
    String text = value;
    for (int x = 0; x < length - value.length(); x++) text = pad + text;
    return text;
}

You can use the above method addLeadingText(length, padding text, your text)

addLeadingText(8, "0", "Apple");

The output would be 000Apple

It isn't pretty, but it works. If you have access apache commons i would suggest that use that

if (val.length() < 8) {
  for (int i = 0; i < val - 8; i++) {
    val = "0" + val;
  }
}