[java] Generate fixed length Strings filled with whitespaces

I need to produce fixed length string to generate a character position based file. The missing characters must be filled with space character.

As an example, the field CITY has a fixed length of 15 characters. For the inputs "Chicago" and "Rio de Janeiro" the outputs are

"        Chicago"
" Rio de Janeiro"

public static String padString(String word, int length) {
    String newWord = word;
    for(int count = word.length(); count < length; count++) {
        newWord = " " + newWord;
    }
    return newWord;
}

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

This simple function works for me:

public static String leftPad(String string, int length, String pad) {
      return pad.repeat(length - string.length()) + string;
    }

Invocation:

String s = leftPad(myString, 10, "0");

Here's a neat trick:

// E.g pad("sss","00000000"); should deliver "00000sss".
public static String pad(String string, String pad) {
  /*
   * Add the pad to the left of string then take as many characters from the right 
   * that is the same length as the pad.
   * This would normally mean starting my substring at 
   * pad.length() + string.length() - pad.length() but obviously the pad.length()'s 
   * cancel.
   *
   * 00000000sss
   *    ^ ----- Cut before this character - pos = 8 + 3 - 8 = 3
   */
  return (pad + string).substring(string.length());
}

public static void main(String[] args) throws InterruptedException {
  try {
    System.out.println("Pad 'Hello' with '          ' produces: '"+pad("Hello","          ")+"'");
    // Prints: Pad 'Hello' with '          ' produces: '     Hello'
  } catch (Exception e) {
    e.printStackTrace();
  }
}

This code works great.

  String ItemNameSpacing = new String(new char[10 - masterPojos.get(i).getName().length()]).replace('\0', ' ');
  printData +=  masterPojos.get(i).getName()+ "" + ItemNameSpacing + ":   " + masterPojos.get(i).getItemQty() +" "+ masterPojos.get(i).getItemMeasure() + "\n";

Happy Coding!!

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.

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.

Here is the code with tests cases ;) :

@Test
public void testNullStringShouldReturnStringWithSpaces() throws Exception {
    String fixedString = writeAtFixedLength(null, 5);
    assertEquals(fixedString, "     ");
}

@Test
public void testEmptyStringReturnStringWithSpaces() throws Exception {
    String fixedString = writeAtFixedLength("", 5);
    assertEquals(fixedString, "     ");
}

@Test
public void testShortString_ReturnSameStringPlusSpaces() throws Exception {
    String fixedString = writeAtFixedLength("aa", 5);
    assertEquals(fixedString, "aa   ");
}

@Test
public void testLongStringShouldBeCut() throws Exception {
    String fixedString = writeAtFixedLength("aaaaaaaaaa", 5);
    assertEquals(fixedString, "aaaaa");
}


private String writeAtFixedLength(String pString, int lenght) {
    if (pString != null && !pString.isEmpty()){
        return getStringAtFixedLength(pString, lenght);
    }else{
        return completeWithWhiteSpaces("", lenght);
    }
}

private String getStringAtFixedLength(String pString, int lenght) {
    if(lenght < pString.length()){
        return pString.substring(0, lenght);
    }else{
        return completeWithWhiteSpaces(pString, lenght - pString.length());
    }
}

private String completeWithWhiteSpaces(String pString, int lenght) {
    for (int i=0; i<lenght; i++)
        pString += " ";
    return pString;
}

I like TDD ;)

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;
    }

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

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);
}

String.format("%15s",s) // pads right
String.format("%-15s",s) // pads left

Great summary here