Generate fixed length Strings filled with whitespaces

Question

Since Java 1.5 we can use the method java.lang.String.format(String, Object...) and use printf like format.

The format string "%1$15s" do the job. Where 1$ indicates the argument index, s indicates that the argument is a String and 15 represents the minimal width of the String. Putting it all together: "%1$15s".

For a general method we have:

public static String fixedLengthString(String string, int length) {
    return String.format("%1$"+length+ "s", string);
}

Maybe someone can suggest another format string to fill the empty spaces with an specific character?

Utilize String.format's padding with spaces and replace them with the desired char.

String toPad = "Apple";
String padded = String.format("%8s", toPad).replace(' ', '0');
System.out.println(padded);

Prints 000Apple.

---

Update more performant version (since it does not rely on String.format), that has no problem with spaces (thx to Rafael Borja for the hint).

int width = 10;
char fill = '0';

String toPad = "New York";
String padded = new String(new char[width - toPad.length()]).replace('\0', fill) + toPad;
System.out.println(padded);

Prints 00New York.

But a check needs to be added to prevent the attempt of creating a char array with negative length.

This code will have exactly the given amount of characters; filled with spaces or truncated on the right side:

private String leftpad(String text, int length) {
    return String.format("%" + length + "." + length + "s", text);
}

private String rightpad(String text, int length) {
    return String.format("%-" + length + "." + length + "s", text);
}

For right pad you need String.format("%0$-15s", str)

i.e. - sign will "right" pad and no - sign will "left" pad

See my example:

import java.util.Scanner;
 
public class Solution {
 
    public static void main(String[] args) {
            Scanner sc=new Scanner(System.in);
            System.out.println("================================");
            for(int i=0;i<3;i++)
            {
                String s1=sc.nextLine();
                
                
                Scanner line = new Scanner( s1);
                line=line.useDelimiter(" ");
               
                String language = line.next();
                int mark = line.nextInt();;
                
                System.out.printf("%s%03d\n",String.format("%0$-15s", language),mark);
                
            }
            System.out.println("================================");
 
    }
}

The input must be a string and a number

example input : Google 1

You can also write a simple method like below

public static String padString(String str, int leng) {
        for (int i = str.length(); i <= leng; i++)
            str += " ";
        return str;
    }

import org.apache.commons.lang3.StringUtils;

String stringToPad = "10";
int maxPadLength = 10;
String paddingCharacter = " ";

StringUtils.leftPad(stringToPad, maxPadLength, paddingCharacter)

Way better than Guava imo. Never seen a single enterprise Java project that uses Guava but Apache String Utils is incredibly common.

The Guava Library has Strings.padStart that does exactly what you want, along with many other useful utilities.