How can I pad a String in Java

Question

Is there some easy way to pad Strings in Java   Seems like something that should be in some StringUtil-like API  but I can t find anything that does this

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java util Formatter will do left and right padding  No need for odd third party dependencies  would you want to add them for something so trivial     I ve left out the details and made this post  community wiki  as it is not something I have a need for

User · Answer

Use this function   private String leftPadding String word  int length  char ch       return  length  gt  word length      leftPadding ch   word  length  ch    word      how to use    leftPadding month  2   0      output  01 02 03 04    11 12

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public static String padLeft String in  int size  char padChar                        if  in length    lt   size            char   temp   new char size              Llenado Array con el padChar           for int i  0 i lt size i                 temp i   padChar                    int posIniTemp   size-in length            for int i 0 i lt in length   i                 temp posIniTemp  in charAt i               posIniTemp                                  return new String temp             return

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Have a look at org apache commons lang StringUtils rightPad String str  int size  char padChar   But the algorithm is very simple  pad right up to size chars   public String pad String str  int size  char padChar      StringBuilder padded   new StringBuilder str     while  padded length    lt  size          padded append padChar         return padded toString

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Have a look at org apache commons lang StringUtils rightPad String str  int size  char padChar   But the algorithm is very simple  pad right up to size chars   public String pad String str  int size  char padChar      StringBuilder padded   new StringBuilder str     while  padded length    lt  size          padded append padChar         return padded toString

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In Guava  this is easy   Strings padStart  string   10        Strings padEnd  string   10

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You can reduce the per-call overhead by retaining the padding data  rather than rebuilding it every time   public class RightPadder        private int length      private String padding       public RightPadder int length  String pad            this length   length          StringBuilder sb   new StringBuilder pad           while  sb length    lt  length                sb append sb                     padding   sb toString              public String pad String s            return  s length    lt  length   s   padding   s  substring 0  length              As an alternative  you can make the result length a parameter to the pad      method  In that case do the adjustment of the hidden padding in that method instead of in the constructor    Hint  For extra credit  make it thread-safe   -

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Since Java 1 5  String format   can be used to left right pad a given string   public static String padRight String s  int n         return String format   -    n    s   s        public static String padLeft String s  int n        return String format       n    s   s             public static void main String args    throws Exception    System out println padRight  Howto   20           System out println padLeft  Howto   20              And the output is   Howto                                Howto

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This took me a little while to figure out  The real key is to read that Formatter documentation      Get your data from wherever  final byte   data   getData       Get the digest engine  final MessageDigest md5  MessageDigest getInstance  MD5       Send your data through it  md5 update data      Parse the data as a positive BigInteger  final BigInteger digest   new BigInteger 1 md5 digest        Pad the digest with blanks  32 wide  String hex   String format         See  http   download oracle com javase 1 5 0 docs api java util Formatter html        Format    argument index   flags  width conversion        Conversion   x    X   integral    The result is formatted as a hexadecimal integer       1 32x       digest       Replace the blank padding with 0s  hex   hex replace      0    System out println hex

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Here is another way to pad to the right      put the number of spaces  or any character you like  in your paddedString  String paddedString    --------------------    String myStringToBePadded    I like donuts    myStringToBePadded   myStringToBePadded   paddedString substring myStringToBePadded length        result  myStringToBePadded    I like donuts-------

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Since Java 11  String repeat int  can be used to left right pad a given string   System out println     repeat 5   apple    System out println  apple      repeat 5      Output        apple apple

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A simple solution would be   package nl  public class Padder       public static void main String   args            String s    123            System out println                s  substring s length

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A lot of people have some very interesting techniques but I like to keep it simple so I go with this     public static String padRight String s  int n  char padding       StringBuilder builder   new StringBuilder s length     n       builder append s       for int i   0  i  lt  n  i             builder append padding             return builder toString       public static String padLeft String s  int n   char padding        StringBuilder builder   new StringBuilder s length     n       for int i   0  i  lt  n  i             builder append Character toString padding              return builder append s  toString       public static String pad String s  int n  char padding       StringBuilder pad   new StringBuilder s length     n   2       StringBuilder value   new StringBuilder n       for int i   0  i  lt  n  i             pad append padding             return value append pad  append s  append pad  toString

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Let s me leave an answer for some cases that you need to give left right padding  or prefix suffix string or spaces  before you concatenate to another string and you don t want to test length or any if condition   The same to the selected answer  I would prefer the StringUtils of Apache Commons but using this way   StringUtils defaultString StringUtils leftPad myString  1     Explain    myString  the string I input  can be null StringUtils leftPad myString  1   if string is null  this statement would return null too then use defaultString to give empty string to prevent concatenate null

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Something simple   The value should be a string  convert it to string  if it s not  Like      123 or Integer toString 123      let s assume value holds the String we want to pad String value    123     Substring start from the value length char index until end length of padded   String padded  00000000  substring value length      value      now padded is  00000123    More precise   pad right   String padded   value     ABCDEFGH  substring value length           now padded is  123DEFGH    pad left   String padString    ABCDEFGH   String padded    padString substring 0  padString length   - value length       value      now padded is  ABCDE123

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Apache StringUtils has several methods  leftPad  rightPad  center and repeat    But please note that     as others have mentioned and demonstrated in this answer     String format   and the Formatter classes in the JDK are better options  Use them over the commons code

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Here is another way to pad to the right      put the number of spaces  or any character you like  in your paddedString  String paddedString    --------------------    String myStringToBePadded    I like donuts    myStringToBePadded   myStringToBePadded   paddedString substring myStringToBePadded length        result  myStringToBePadded    I like donuts-------

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you can use the built in StringBuilder append   and insert   methods  for padding of variable string lengths   AbstractStringBuilder append CharSequence s  int start  int end      For Example   private static final String  MAX STRING                             20 spaces      Set lt StringBuilder gt  set  new HashSet lt StringBuilder gt         set add new StringBuilder  12345678         set add new StringBuilder  123456789         set add new StringBuilder  1234567811         set add new StringBuilder  12345678123         set add new StringBuilder  1234567812234         set add new StringBuilder  1234567812222         set add new StringBuilder  12345678122334          for StringBuilder padMe  set          padMe append MAX STRING  padMe length    MAX STRING length

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Besides Apache Commons  also see String format which should be able to take care of simple padding  e g  with spaces

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A simple solution would be   package nl  public class Padder       public static void main String   args            String s    123            System out println                s  substring s length

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public static String LPad String str  Integer length  char car      return  str   String format       length    s       replace      String valueOf car    substring 0  length      public static String RPad String str  Integer length  char car      return  String format       length    s       replace      String valueOf car     str  substring str length    length   str length        LPad  Hi   10   R     gives  RRRRRRRRHi  RPad  Hi   10   R     gives  HiRRRRRRRR  RPad  Hi   10         gives  Hi          RPad  Hi   1          gives  H    etc

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Since Java 11  String repeat int  can be used to left right pad a given string   System out println     repeat 5   apple    System out println  apple      repeat 5      Output        apple apple

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This works      format   1 -    9    s    XXX   replaceAll       0     It will fill your String XXX up to 9 Chars with a whitespace  After that all Whitespaces will be replaced with a 0  You can change the whitespace and the 0 to whatever you want

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A lot of people have some very interesting techniques but I like to keep it simple so I go with this     public static String padRight String s  int n  char padding       StringBuilder builder   new StringBuilder s length     n       builder append s       for int i   0  i  lt  n  i             builder append padding             return builder toString       public static String padLeft String s  int n   char padding        StringBuilder builder   new StringBuilder s length     n       for int i   0  i  lt  n  i             builder append Character toString padding              return builder append s  toString       public static String pad String s  int n  char padding       StringBuilder pad   new StringBuilder s length     n   2       StringBuilder value   new StringBuilder n       for int i   0  i  lt  n  i             pad append padding             return value append pad  append s  append pad  toString

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How is this  String is  hello  and required padding is 15 with  0  left pad  String ax  Hello   while ax length    lt  15  ax  0  ax

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Java oneliners  no fancy library       6 characters padding example String pad                testcases for 0  4  8 characters String input         abcd     abcdefgh    Pad Left  don t limit  result   pad substring Math min input length   pad length       input  results                abcd     abcdefgh    Pad Right  don t limit  result   input   pad substring Math min input length   pad length      results              abcd       abcdefgh    Pad Left  limit to pad length  result    pad   input  substring input length    input length     pad length     results                abcd     cdefgh    Pad Right  limit to pad length  result    input   pad  substring 0  pad length     results              abcd       abcdef

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Apache StringUtils has several methods  leftPad  rightPad  center and repeat    But please note that     as others have mentioned and demonstrated in this answer     String format   and the Formatter classes in the JDK are better options  Use them over the commons code

User · Answer

Apache StringUtils has several methods  leftPad  rightPad  center and repeat    But please note that     as others have mentioned and demonstrated in this answer     String format   and the Formatter classes in the JDK are better options  Use them over the commons code

User · Answer

Since Java 1 5  String format   can be used to left right pad a given string   public static String padRight String s  int n         return String format   -    n    s   s        public static String padLeft String s  int n        return String format       n    s   s             public static void main String args    throws Exception    System out println padRight  Howto   20           System out println padLeft  Howto   20              And the output is   Howto                                Howto

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Padding to 10 characters   String format   10s    foo   replace            String format   -10s    bar   replace            String format   10s    longer than 10 chars   replace              output            foo   bar          longer than 10 chars   Display     for characters of password   String password    secret123   String padded   String format     password length    s       replace              output has the same length as the password string     secret123

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i know this thread is kind of old and the original question was for an easy solution but if it s supposed to be really fast  you should use a char array   public static String pad String str  int size  char padChar        if  str length    lt  size                char   temp   new char size           int i   0           while  i  lt  str length                          temp i    str charAt i               i                       while  i  lt  size                        temp i    padChar              i                       str   new String temp              return str      the formatter solution is not optimal  just building the format string creates 2 new strings   apache s solution can be improved by initializing the sb with the target size so replacing below  StringBuffer padded   new StringBuffer str      with      StringBuffer padded   new StringBuffer pad    padded append value     would prevent the sb s internal buffer from growing

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A simple solution without any API will be as follows   public String pad String num  int len       if len-num length    lt  0  return num      StringBuffer sb   new StringBuffer        for i 0  i lt  len-num length     i             sb append  0              sb append num       return sb toString

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Since Java 1 5  String format   can be used to left right pad a given string   public static String padRight String s  int n         return String format   -    n    s   s        public static String padLeft String s  int n        return String format       n    s   s             public static void main String args    throws Exception    System out println padRight  Howto   20           System out println padLeft  Howto   20              And the output is   Howto                                Howto

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Java oneliners  no fancy library       6 characters padding example String pad                testcases for 0  4  8 characters String input         abcd     abcdefgh    Pad Left  don t limit  result   pad substring Math min input length   pad length       input  results                abcd     abcdefgh    Pad Right  don t limit  result   input   pad substring Math min input length   pad length      results              abcd       abcdefgh    Pad Left  limit to pad length  result    pad   input  substring input length    input length     pad length     results                abcd     cdefgh    Pad Right  limit to pad length  result    input   pad  substring 0  pad length     results              abcd       abcdef

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Let s me leave an answer for some cases that you need to give left right padding  or prefix suffix string or spaces  before you concatenate to another string and you don t want to test length or any if condition   The same to the selected answer  I would prefer the StringUtils of Apache Commons but using this way   StringUtils defaultString StringUtils leftPad myString  1     Explain    myString  the string I input  can be null StringUtils leftPad myString  1   if string is null  this statement would return null too then use defaultString to give empty string to prevent concatenate null

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public static String padLeft String in  int size  char padChar                        if  in length    lt   size            char   temp   new char size              Llenado Array con el padChar           for int i  0 i lt size i                 temp i   padChar                    int posIniTemp   size-in length            for int i 0 i lt in length   i                 temp posIniTemp  in charAt i               posIniTemp                                  return new String temp             return

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java util Formatter will do left and right padding  No need for odd third party dependencies  would you want to add them for something so trivial     I ve left out the details and made this post  community wiki  as it is not something I have a need for

User · Answer

Apache StringUtils has several methods  leftPad  rightPad  center and repeat    But please note that     as others have mentioned and demonstrated in this answer     String format   and the Formatter classes in the JDK are better options  Use them over the commons code

User · Answer

This took me a little while to figure out  The real key is to read that Formatter documentation      Get your data from wherever  final byte   data   getData       Get the digest engine  final MessageDigest md5  MessageDigest getInstance  MD5       Send your data through it  md5 update data      Parse the data as a positive BigInteger  final BigInteger digest   new BigInteger 1 md5 digest        Pad the digest with blanks  32 wide  String hex   String format         See  http   download oracle com javase 1 5 0 docs api java util Formatter html        Format    argument index   flags  width conversion        Conversion   x    X   integral    The result is formatted as a hexadecimal integer       1 32x       digest       Replace the blank padding with 0s  hex   hex replace      0    System out println hex

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Padding to 10 characters   String format   10s    foo   replace            String format   -10s    bar   replace            String format   10s    longer than 10 chars   replace              output            foo   bar          longer than 10 chars   Display     for characters of password   String password    secret123   String padded   String format     password length    s       replace              output has the same length as the password string     secret123

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you can use the built in StringBuilder append   and insert   methods  for padding of variable string lengths   AbstractStringBuilder append CharSequence s  int start  int end      For Example   private static final String  MAX STRING                             20 spaces      Set lt StringBuilder gt  set  new HashSet lt StringBuilder gt         set add new StringBuilder  12345678         set add new StringBuilder  123456789         set add new StringBuilder  1234567811         set add new StringBuilder  12345678123         set add new StringBuilder  1234567812234         set add new StringBuilder  1234567812222         set add new StringBuilder  12345678122334          for StringBuilder padMe  set          padMe append MAX STRING  padMe length    MAX STRING length

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How about using recursion   Solution given below is compatible with all JDK versions and no external libraries required     private static String addPadding final String str  final int desiredLength  final String padBy            String result   str          if  str length    gt   desiredLength                return result            else               result    padBy              return addPadding result  desiredLength  padBy                     NOTE  This solution will append the padding  with a little tweak you can prefix the pad value

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Have a look at org apache commons lang StringUtils rightPad String str  int size  char padChar   But the algorithm is very simple  pad right up to size chars   public String pad String str  int size  char padChar      StringBuilder padded   new StringBuilder str     while  padded length    lt  size          padded append padChar         return padded toString

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ck s and  Marlon Tarak s answers are the only ones to use a char    which for applications that have several calls to padding methods per second is the best approach   However  they don t take advantage of any array manipulation optimizations and are a little overwritten for my taste  this can be done with no loops at all   public static String pad String source  char fill  int length  boolean right       if source length    gt  length  return source      char   out   new char length       if right           System arraycopy source toCharArray    0  out  0  source length             Arrays fill out  source length    length  fill        else          int sourceOffset   length - source length            System arraycopy source toCharArray    0  out  sourceOffset  source length             Arrays fill out  0  sourceOffset  fill             return new String out       Simple test method   public static void main String    args       System out println  012345678901234567890123456789        System out println pad  cats        30  true        System out println pad  cats        30  false        System out println pad  cats        20  false        System out println pad  cats        30  true        System out println pad  too long for your own good  buddy        30  true        Outputs   012345678901234567890123456789 cats                                                     cats                 cats cats                           too long for your own good  buddy

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ck s and  Marlon Tarak s answers are the only ones to use a char    which for applications that have several calls to padding methods per second is the best approach   However  they don t take advantage of any array manipulation optimizations and are a little overwritten for my taste  this can be done with no loops at all   public static String pad String source  char fill  int length  boolean right       if source length    gt  length  return source      char   out   new char length       if right           System arraycopy source toCharArray    0  out  0  source length             Arrays fill out  source length    length  fill        else          int sourceOffset   length - source length            System arraycopy source toCharArray    0  out  sourceOffset  source length             Arrays fill out  0  sourceOffset  fill             return new String out       Simple test method   public static void main String    args       System out println  012345678901234567890123456789        System out println pad  cats        30  true        System out println pad  cats        30  false        System out println pad  cats        20  false        System out println pad  cats        30  true        System out println pad  too long for your own good  buddy        30  true        Outputs   012345678901234567890123456789 cats                                                     cats                 cats cats                           too long for your own good  buddy

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This works      format   1 -    9    s    XXX   replaceAll       0     It will fill your String XXX up to 9 Chars with a whitespace  After that all Whitespaces will be replaced with a 0  You can change the whitespace and the 0 to whatever you want

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You can reduce the per-call overhead by retaining the padding data  rather than rebuilding it every time   public class RightPadder        private int length      private String padding       public RightPadder int length  String pad            this length   length          StringBuilder sb   new StringBuilder pad           while  sb length    lt  length                sb append sb                     padding   sb toString              public String pad String s            return  s length    lt  length   s   padding   s  substring 0  length              As an alternative  you can make the result length a parameter to the pad      method  In that case do the adjustment of the hidden padding in that method instead of in the constructor    Hint  For extra credit  make it thread-safe   -

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public static String LPad String str  Integer length  char car      return  str   String format       length    s       replace      String valueOf car    substring 0  length      public static String RPad String str  Integer length  char car      return  String format       length    s       replace      String valueOf car     str  substring str length    length   str length        LPad  Hi   10   R     gives  RRRRRRRRHi  RPad  Hi   10   R     gives  HiRRRRRRRR  RPad  Hi   10         gives  Hi          RPad  Hi   1          gives  H    etc

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Besides Apache Commons  also see String format which should be able to take care of simple padding  e g  with spaces

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A simple solution without any API will be as follows   public String pad String num  int len       if len-num length    lt  0  return num      StringBuffer sb   new StringBuffer        for i 0  i lt  len-num length     i             sb append  0              sb append num       return sb toString

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Something simple   The value should be a string  convert it to string  if it s not  Like      123 or Integer toString 123      let s assume value holds the String we want to pad String value    123     Substring start from the value length char index until end length of padded   String padded  00000000  substring value length      value      now padded is  00000123    More precise   pad right   String padded   value     ABCDEFGH  substring value length           now padded is  123DEFGH    pad left   String padString    ABCDEFGH   String padded    padString substring 0  padString length   - value length       value      now padded is  ABCDE123

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Use this function   private String leftPadding String word  int length  char ch       return  length  gt  word length      leftPadding ch   word  length  ch    word      how to use    leftPadding month  2   0      output  01 02 03 04    11 12

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This utility class that is useful for left pad and zero fill of Strings  I hope that it helps someone  package your package name          Utility class for left pad and zero fill of Strings          public class LeftPad        public static String lpad String string  int length  char fill            return new String lpad string toCharArray    length  fill               public static String zerofill String string  int length            return new String zerofill string toCharArray    length               private static char   lpad char   chars  int length  char fill             int delta   0          int limit   0           if  length  gt  chars length                delta   length - chars length              limit   length            else               delta   0              limit   chars length                     char   output   new char chars length   delta           for  int i   0  i  lt  limit  i                  if  i  lt  delta                    output i    fill                else                   output i    chars i - delta                                   return output             private static char   zerofill char   chars  int length            return lpad chars  length   0                          For tests              public static void main String   args             String string    quot 123 quot           char pad                 System out println  quot left pad blank   quot    string           System out println  quot Result    quot    LeftPad lpad string  10  pad     quot   quot             System out println            System out println  quot zero fill   quot    string           System out println  quot Result    quot    LeftPad zerofill string  10     quot   quot              This is the output  left pad blank  123 Result          123   zero fill  123 Result   0000000123

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i know this thread is kind of old and the original question was for an easy solution but if it s supposed to be really fast  you should use a char array   public static String pad String str  int size  char padChar        if  str length    lt  size                char   temp   new char size           int i   0           while  i  lt  str length                          temp i    str charAt i               i                       while  i  lt  size                        temp i    padChar              i                       str   new String temp              return str      the formatter solution is not optimal  just building the format string creates 2 new strings   apache s solution can be improved by initializing the sb with the target size so replacing below  StringBuffer padded   new StringBuffer str      with      StringBuffer padded   new StringBuffer pad    padded append value     would prevent the sb s internal buffer from growing

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Besides Apache Commons  also see String format which should be able to take care of simple padding  e g  with spaces

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You can reduce the per-call overhead by retaining the padding data  rather than rebuilding it every time   public class RightPadder        private int length      private String padding       public RightPadder int length  String pad            this length   length          StringBuilder sb   new StringBuilder pad           while  sb length    lt  length                sb append sb                     padding   sb toString              public String pad String s            return  s length    lt  length   s   padding   s  substring 0  length              As an alternative  you can make the result length a parameter to the pad      method  In that case do the adjustment of the hidden padding in that method instead of in the constructor    Hint  For extra credit  make it thread-safe   -

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All string operation usually needs to be very efficient - especially if you are working with big sets of data  I wanted something that s fast and flexible  similar to what you will get in plsql pad command  Also  I don t want to include a huge lib for just one small thing  With these considerations none of these solutions were satisfactory  This is the solutions I came up with  that had the best bench-marking results  if anybody can improve on it  please add your comment   public static char   lpad char   pStringChar  int pTotalLength  char pPad        if  pStringChar length  lt  pTotalLength            char   retChar   new char pTotalLength           int padIdx   pTotalLength - pStringChar length          Arrays fill retChar  0  padIdx  pPad           System arraycopy pStringChar  0  retChar  padIdx  pStringChar length           return retChar        else           return pStringChar             note it is called with String toCharArray   and the result can be converted to String with new String  char   result   The reason for this is  if you applying multiple operations you can do them all on char   and not keep on converting between formats - behind the scenes  String is stored as char    If these operations were included in the String class itself  it would have been twice as efficient - speed and memory wise

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Since Java 1 5  String format   can be used to left right pad a given string   public static String padRight String s  int n         return String format   -    n    s   s        public static String padLeft String s  int n        return String format       n    s   s             public static void main String args    throws Exception    System out println padRight  Howto   20           System out println padLeft  Howto   20              And the output is   Howto                                Howto

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How is this  String is  hello  and required padding is 15 with  0  left pad  String ax  Hello   while ax length    lt  15  ax  0  ax

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Here s a parallel version for those of you that have very long Strings  -   int width   100  String s    129018    CharSequence padded   IntStream range 0 width               parallel                map i- gt i- width-s length                  map i- gt i lt 0    0   s charAt i                collect StringBuilder  new   sb c - gt  sb append  char c    sb1 sb2 - gt sb1 append sb2

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How about using recursion   Solution given below is compatible with all JDK versions and no external libraries required     private static String addPadding final String str  final int desiredLength  final String padBy            String result   str          if  str length    gt   desiredLength                return result            else               result    padBy              return addPadding result  desiredLength  padBy                     NOTE  This solution will append the padding  with a little tweak you can prefix the pad value

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Here s a parallel version for those of you that have very long Strings  -   int width   100  String s    129018    CharSequence padded   IntStream range 0 width               parallel                map i- gt i- width-s length                  map i- gt i lt 0    0   s charAt i                collect StringBuilder  new   sb c - gt  sb append  char c    sb1 sb2 - gt sb1 append sb2

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java util Formatter will do left and right padding  No need for odd third party dependencies  would you want to add them for something so trivial     I ve left out the details and made this post  community wiki  as it is not something I have a need for

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Have a look at org apache commons lang StringUtils rightPad String str  int size  char padChar   But the algorithm is very simple  pad right up to size chars   public String pad String str  int size  char padChar      StringBuilder padded   new StringBuilder str     while  padded length    lt  size          padded append padChar         return padded toString

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Found this on Dzone  Pad with zeros   String format    020d    93      prints   00000000000000000093

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Found this on Dzone  Pad with zeros   String format    020d    93      prints   00000000000000000093

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Besides Apache Commons  also see String format which should be able to take care of simple padding  e g  with spaces

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In Guava  this is easy   Strings padStart  string   10        Strings padEnd  string   10

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All string operation usually needs to be very efficient - especially if you are working with big sets of data  I wanted something that s fast and flexible  similar to what you will get in plsql pad command  Also  I don t want to include a huge lib for just one small thing  With these considerations none of these solutions were satisfactory  This is the solutions I came up with  that had the best bench-marking results  if anybody can improve on it  please add your comment   public static char   lpad char   pStringChar  int pTotalLength  char pPad        if  pStringChar length  lt  pTotalLength            char   retChar   new char pTotalLength           int padIdx   pTotalLength - pStringChar length          Arrays fill retChar  0  padIdx  pPad           System arraycopy pStringChar  0  retChar  padIdx  pStringChar length           return retChar        else           return pStringChar             note it is called with String toCharArray   and the result can be converted to String with new String  char   result   The reason for this is  if you applying multiple operations you can do them all on char   and not keep on converting between formats - behind the scenes  String is stored as char    If these operations were included in the String class itself  it would have been twice as efficient - speed and memory wise

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java util Formatter will do left and right padding  No need for odd third party dependencies  would you want to add them for something so trivial     I ve left out the details and made this post  community wiki  as it is not something I have a need for

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You can reduce the per-call overhead by retaining the padding data  rather than rebuilding it every time   public class RightPadder        private int length      private String padding       public RightPadder int length  String pad            this length   length          StringBuilder sb   new StringBuilder pad           while  sb length    lt  length                sb append sb                     padding   sb toString              public String pad String s            return  s length    lt  length   s   padding   s  substring 0  length              As an alternative  you can make the result length a parameter to the pad      method  In that case do the adjustment of the hidden padding in that method instead of in the constructor    Hint  For extra credit  make it thread-safe   -

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This utility class that is useful for left pad and zero fill of Strings  I hope that it helps someone  package your package name          Utility class for left pad and zero fill of Strings          public class LeftPad        public static String lpad String string  int length  char fill            return new String lpad string toCharArray    length  fill               public static String zerofill String string  int length            return new String zerofill string toCharArray    length               private static char   lpad char   chars  int length  char fill             int delta   0          int limit   0           if  length  gt  chars length                delta   length - chars length              limit   length            else               delta   0              limit   chars length                     char   output   new char chars length   delta           for  int i   0  i  lt  limit  i                  if  i  lt  delta                    output i    fill                else                   output i    chars i - delta                                   return output             private static char   zerofill char   chars  int length            return lpad chars  length   0                          For tests              public static void main String   args             String string    quot 123 quot           char pad                 System out println  quot left pad blank   quot    string           System out println  quot Result    quot    LeftPad lpad string  10  pad     quot   quot             System out println            System out println  quot zero fill   quot    string           System out println  quot Result    quot    LeftPad zerofill string  10     quot   quot              This is the output  left pad blank  123 Result          123   zero fill  123 Result   0000000123

[java] How can I pad a String in Java?

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