Create a string with n characters

Question

Is there a way in java to create a string with a specified number of a specified character   In my case  I would need to create a string with 10 spaces   My current code is   StringBuffer outputBuffer   new StringBuffer length   for  int i   0  i  lt  length  i        outputBuffer append         return outputBuffer toString      Is there a better way to accomplish the same thing   In particular I d like something that is fast  in terms of execution

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Hmm now that I think about it  maybe Arrays fill   char   charArray   new char length   Arrays fill charArray        String str   new String charArray     Of course  I assume that the fill method does the same thing as your code  so it will probably perform about the same  but at least this is fewer lines

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I think this is the less code it s possible  it uses Guava Joiner class       Joiner on     join Collections nCopies 10

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How about this   char   bytes   new char length   Arrays fill bytes        String str   new String bytes

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In most cases you only need Strings upto a certains length  say 100 spaces  You could prepare an array of Strings where the index number is equal to the size of the space-filled string and lookup the string  if the required length is within the limits or create it on demand if it s outside the boundary

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Have a method like this  This appends required spaces at the end of the given String to make a given String to length of specific length    public static String fillSpaces  String str            the spaces string should contain spaces exceeding the max needed     String spaces                                                              return str   spaces substring str length

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since Java 11   quot   quot  repeat 10     since Java 8  generate    - gt   quot   quot   limit 10  collect joining      where  import static java util stream Collectors joining  import static java util stream Stream generate

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how about this    public String fillSpaces int len           the spaces string should contain spaces exceeding the max needed          String spaces                                                              return spaces substring 0 len       EDIT  I ve written a simple code to test the concept and here what i found    Method 1  adding single space in a loop     public String execLoopSingleSpace int len       StringBuilder sb   new StringBuilder         for int i 0  i  lt  len  i              sb append                  return sb toString          Method 2  append 100 spaces and loop  then substring     public String execLoopHundredSpaces int len       StringBuilder sb   new StringBuilder                            append               append               append                            append               append               append                            append               append               append                     for  int i 0  i  lt  len 100   i              sb append                            append               append               append                            append               append               append                            append               append               append                           return sb toString   substring 0 len         The result I get creating 12 345 678 spaces   C  docs Projects gt  java FillSpace 12345678 method 1  append single spaces for 12345678 times  Time taken is   234ms    Length of String is 12345678 method 2  append 100 spaces for 123456 times  Time taken is   141ms    Length of String is 12345678 Process java exited with code 0   and for 10 000 000 spaces   C  docs Projects gt  java FillSpace 10000000 method 1  append single spaces for 10000000 times  Time taken is   157ms    Length of String is 10000000 method 2  append 100 spaces for 100000 times  Time taken is   109ms    Length of String is 10000000 Process java exited with code 0   combining direct allocation and iteration always takes less time  on average 60ms less when creating huge spaces  For smaller sizes  both results are negligible    But please continue to comment  -

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You can replace StringBuffer with StringBuilder   the latter is not synchronized  may be a faster in a single thread app     And you can create the StringBuilder instance once  instead of creating it each time you need it    Something like this   class BuildString        private final StringBuilder builder   new StringBuilder         public String stringOf  char c   int times               for  int i   0   i  lt  times   i                     builder append  c                        String result   builder toString             builder delete  0   builder length   -1             return result                 And use it like this    BuildString createA   new BuildString     String empty   createA stringOf       10      If you hold your createA as a instance variable  you may save time creating instances   This is not thread safe  if you have multi threads  each thread should have its own copy

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Use StringUtils  StringUtils repeat      10

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Since Java 11 you can simply use String repeat count  to solve your problem   Returns a string whose value is the concatenation of this string repeated count times  If this string is empty or count is zero then the empty string is returned   So instead of a loop your code would just look like this   quot   quot  repeat length

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In Java 8 you can use String join   String join     Collections nCopies n  s

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int c   10  String spaces   String format      c   c         this will solve your problem

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My contribution based on the algorithm for fast exponentiation          Repeats the given   link String  n times          param str               the   link String  to repeat      param n               the repetition count      throws IllegalArgumentException                when the given repetition count is smaller than zero      return the given   link String  repeated n times      public static String repeat String str  int n        if  n  lt  0          throw new IllegalArgumentException                   the given repetition count is smaller than zero         else if  n    0          return         else if  n    1          return str      else if  n   2    0            String s   repeat str  n   2           return s concat s         else         return str concat repeat str  n - 1        I tested the algorithm against two other approaches    Regular for loop using String concat   to concatenate string Regular for loop using a StringBuilder   Test code  concatenation using a for loop and String concat   becomes to slow for large n  so I left it out after the 5th iteration           Test the string concatenation operation          param args     public static void main String   args        long startTime      String str             int n   1      for  int j   0  j  lt  9    j            n    10          System out format  Performing test with n  d n   n            startTime   System currentTimeMillis            StringUtil repeat str  n           System out                  format   tStringUtil repeat   concatenation performed in     d milliseconds n                           System currentTimeMillis   - startTime            if  j  lt 5                startTime   System currentTimeMillis                String string                   for  int i   0  i  lt  n    i                  string   string concat str               System out                      format   tString concat   concatenation performed in         d milliseconds n                               System currentTimeMillis   - startTime             else             System out                      format   tString concat   concatenation performed in        x milliseconds n            startTime   System currentTimeMillis            StringBuilder b   new StringBuilder            for  int i   0  i  lt  n    i              b append str           b toString            System out                  format   tStringBuilder append   concatenation performed in  d milliseconds n                           System currentTimeMillis   - startTime             Results   Performing test with n 10     StringUtil repeat   concatenation performed in    0 milliseconds     String concat   concatenation performed in        0 milliseconds     StringBuilder append   concatenation performed in 0 milliseconds Performing test with n 100     StringUtil repeat   concatenation performed in    0 milliseconds     String concat   concatenation performed in        1 milliseconds     StringBuilder append   concatenation performed in 0 milliseconds Performing test with n 1000     StringUtil repeat   concatenation performed in    0 milliseconds     String concat   concatenation performed in        1 milliseconds     StringBuilder append   concatenation performed in 1 milliseconds Performing test with n 10000     StringUtil repeat   concatenation performed in    0 milliseconds     String concat   concatenation performed in        43 milliseconds     StringBuilder append   concatenation performed in 5 milliseconds Performing test with n 100000     StringUtil repeat   concatenation performed in    0 milliseconds     String concat   concatenation performed in        1579 milliseconds     StringBuilder append   concatenation performed in 1 milliseconds Performing test with n 1000000     StringUtil repeat   concatenation performed in    0 milliseconds     String concat   concatenation performed in        x milliseconds     StringBuilder append   concatenation performed in 10 milliseconds Performing test with n 10000000     StringUtil repeat   concatenation performed in    7 milliseconds     String concat   concatenation performed in        x milliseconds     StringBuilder append   concatenation performed in 112 milliseconds Performing test with n 100000000     StringUtil repeat   concatenation performed in    80 milliseconds     String concat   concatenation performed in        x milliseconds     StringBuilder append   concatenation performed in 1107 milliseconds Performing test with n 1000000000     StringUtil repeat   concatenation performed in    1372 milliseconds     String concat   concatenation performed in        x milliseconds     StringBuilder append   concatenation performed in 12125 milliseconds   Conclusion    For large n - use the recursive approach For small n - for loop has sufficient speed

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Want String to be of fixed size  so you either pad or truncate  for tabulating data     class Playground       private static String fixStrSize String s  int n            return String format   -    n    s   String format        n   s   s               public static void main String    args            System out println     fixStrSize  Hell  8                System out println     fixStrSize  Hells Bells Java Smells  8                     Hell       Hells Be      Excellent reference here

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For good performance  combine answers from aznilamir and from FrustratedWithFormsDesigner  private static final String BLANKS                              private static String getBlankLine  int length         if  length  lt   BLANKS length                   return BLANKS substring  0  length              else               char   array   new char  length            Arrays fill  array                 return new String  array              Adjust size of BLANKS depending on your requirements  My specific BLANKS string is about 200 characters length

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You can use standard String format function for generate N spaces  For example    String format   5c           Makes a string with 5 spaces   or  int count   15  String fifteenSpacebars   String format       count    c           Makes a string of 15 spacebars   If you want another symbol to repeat  you must replace spaces with your desired symbol   int count   7  char mySymbol        System out println String format       count    c        replaceAll               mySymbol      Output

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This worked out for me without using any external libraries in Java 8  String sampleText    test  int n   3  String output   String join     Collections nCopies n  sampleText    System out println output     And the output is  testtesttest

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If you want only spaces  then how about   String spaces    n  0     String format     n  s          which will result in abs n  spaces

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Considering we have   String c    c      character to repeat  for empty it would be      int n   4     number of times to repeat String EMPTY STRING          empty string  can be put in utility class    Java 8  Using Stream   String resultOne   IntStream range 0 n      mapToObj i- gt c  collect Collectors joining EMPTY STRING       cccc   Java 8  Using nCopies   String resultTwo   String join EMPTY STRING  Collections nCopies n  c      cccc

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Just replace your StringBuffer with a StringBuilder  Hard to beat that   If your length is a big number  you might implement some more efficient   but more clumsy  self-appendding  duplicating the length in each iteration    public static String dummyString char c  int len      if  len  lt  1   return       StringBuilder sb   new StringBuilder len  append c     int remnant   len - sb length      while remnant   gt  0       if  remnant   gt   sb length     sb append sb      else sb append sb subSequence 0  remnant       remnant    len - sb length          return sb toString         Also  you might try the Arrays fill   aproach  FrustratedWithFormsDesigner s answer

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I highly suggest not to write the loop by hand  You will do that over and over again during the course of your programming career  People reading your code - that includes you - always have to invest time  even if it are just some seconds  to digest the meaning of the loop   Instead reuse one of the available libraries providing code that does just that like StringUtils repeatfrom Apache Commons Lang   StringUtils repeat      length     That way you also do not have to bother about performance  thus all the gory details of StringBuilder  Compiler optimisations etc  are hidden  If the function would turn out as slow it would be a bug of the library   With Java 11 it becomes even easier       repeat length

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Likely the shortest code using the String API  exclusively   String space10   new String new char 10   replace   0          System out println       space10            prints                    As a method  without directly instantiating char   import java nio CharBuffer          Creates a string of spaces that is  spaces  spaces long         param spaces The number of spaces to add to the string      public String spaces  int spaces       return CharBuffer allocate  spaces   toString   replace    0              Invoke using   System out printf     s  n   spaces  10

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A simple method like below can also be used  public static String padString String str  int leng char chr            for  int i   str length    i  lt   leng  i                str    chr          return str

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The for loop will be optimized by the compiler  In such cases like yours you don t need to care about optimization on your own  Trust the compiler   BTW  if there is a way to create a string with n space characters  than it s coded the same way like you just did

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The shortest solution with Guava   Strings repeat      len    Via Simple way to repeat a String in java

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RandomStringUtils has a provision to create a string from given input size  Cant comment on the speed  but its a one liner   RandomStringUtils random 5   t      creates an output       t t t t t   preferable if you dont want to see  0 in your code

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I know of no built-in method for what you re asking about   However  for a small fixed length like 10  your method should be plenty fast

[java] Create a string with n characters

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