Generate fixed length Strings filled with whitespaces

Question

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

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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  amp  amp   pString isEmpty             return getStringAtFixedLength pString  lenght        else          return completeWithWhiteSpaces     lenght            private String getStringAtFixedLength String pString  int lenght        if lenght  lt  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 lt lenght  i            pString             return pString      I like TDD

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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

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For right pad you need String format  quot  0 -15s quot   str  i e  - sign will  quot right quot  pad and no - sign will  quot left quot  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  quot                                  quot                for int i 0 i lt 3 i                                  String s1 sc nextLine                                                      Scanner line   new Scanner  s1                   line line useDelimiter  quot   quot                                    String language   line next                    int mark   line nextInt                                      System out printf  quot  s 03d n quot  String format  quot  0 -15s quot   language  mark                                              System out println  quot                                  quot               The input must be a string and a number example input   Google 1

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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

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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

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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

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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

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You can also write a simple method like below  public static String padString String str  int leng            for  int i   str length    i  lt   leng  i                str                 return str

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public static String padString String word  int length        String newWord   word      for int count   word length    count  lt  length  count              newWord         newWord            return newWord

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String format   15s  s     pads right String format   -15s  s     pads left   Great summary here

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

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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

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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

[java] Generate fixed length Strings filled with whitespaces

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