Split string to equal length substrings in Java

Question

How to split the string  Thequickbrownfoxjumps  to substrings of equal size in Java  Eg   Thequickbrownfoxjumps  of 4 equal size should give the output     Theq   uick   brow   nfox   jump   s     Similar Question   Split string into equal-length substrings in Scala

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I d rather this simple solution   String content    Thequickbrownfoxjumps   while content length    gt  4        System out println content substring 0  4        content   content substring 4     System out println content

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Here s the regex one-liner version   System out println Arrays toString       Thequickbrownfoxjumps  split     lt    G  4            G is a zero-width assertion that matches the position where the previous match ended   If there was no previous match  it matches the beginning of the input  the same as  A   The enclosing lookbehind matches the position that s four characters along from the end of the last match   Both lookbehind and  G are advanced regex features  not supported by all flavors   Furthermore   G is not implemented consistently across the flavors that do support it   This trick will work  for example  in Java  Perl   NET and JGSoft  but not in PHP  PCRE   Ruby 1 9  or TextMate  both Oniguruma    JavaScript s  y  sticky flag  isn t as flexible as  G  and couldn t be used this way even if JS did support lookbehind   I should mention that I don t necessarily recommend this solution if you have other options   The non-regex solutions in the other answers may be longer  but they re also self-documenting  this one s just about the opposite of that      Also  this doesn t work in Android  which doesn t support the use of  G in lookbehinds

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public static List lt String gt  getSplittedString String stringtoSplit              int length             List lt String gt  returnStringList   new ArrayList lt String gt                    stringtoSplit length     length - 1    length            for  int start   0  start  lt  stringtoSplit length    start    length                returnStringList add stringtoSplit substring start                      Math min stringtoSplit length    start   length                        return returnStringList

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Another brute force solution could be        String input    thequickbrownfoxjumps       int n   input length   4      String   num   new String n        for int i   0  x 0  y 4  i lt n  i         num i     input substring x y       x    4      y    4      System out println num i            Where the code just steps through the string with substrings

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Here is my version based on RegEx and Java 8 streams  It s worth to mention that Matcher results   method is available since Java 9   Test included   public static List lt String gt  splitString String input  int splitSize        Matcher matcher   Pattern compile            splitSize            matcher input       return matcher results   map MatchResult  group  collect Collectors toList         Test public void shouldSplitStringToEqualLengthParts         String anyValidString    Split me equally        String   expectedTokens2     Sp    li    t     me     e    qu    al    ly        String   expectedTokens3     Spl    it     me     equ    all         Assert assertArrayEquals expectedTokens2  splitString anyValidString  2  toArray         Assert assertArrayEquals expectedTokens3  splitString anyValidString  3  toArray

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Java 8 solution  like this but a bit simpler    public static List lt String gt  partition String string  int partSize      List lt String gt  parts   IntStream range 0  string length     partSize       mapToObj i - gt  string substring i   partSize   i   1    partSize        collect toList       if   string length     partSize     0      parts add string substring string length     partSize   partSize      return parts

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public static String   split String src  int len        String   result   new String  int Math ceil  double src length    double len        for  int i 0  i lt result length  i            result i    src substring i len  Math min src length     i 1  len        return result

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I asked  Alan Moore in a comment to the accepted solution how strings with newlines could be handled  He suggested using DOTALL   Using his suggestion I created a small sample of how that works   public void regexDotAllExample   throws UnsupportedEncodingException       final String input    The nquick nbrown r nfox rjumps       final String regex       lt    G  4          Pattern splitByLengthPattern      String   split       splitByLengthPattern   Pattern compile regex       split   splitByLengthPattern split input       System out println  ---- Without DOTALL ----        for  int i   0  i  lt  split length  i              byte   s   split i  getBytes  utf-8            System out println   Idx    i    length    s length    -     s                Output is a single entry longer than the desired split size      ---- Without DOTALL ----      Idx  0  length  26  -  B 17cdc4a5                 DOTALL suggested in Alan Moores comment on SO  https   stackoverflow com a 3761521 1237974     splitByLengthPattern   Pattern compile regex  Pattern DOTALL       split   splitByLengthPattern split input       System out println  ---- With DOTALL ----        for  int i   0  i  lt  split length  i              byte   s   split i  getBytes  utf-8            System out println   Idx    i    length    s length    -     s                Output is as desired 7 entries with each entry having a max length of 4      ---- With DOTALL ----      Idx  0  length  4  -  B 77b22abc      Idx  1  length  4  -  B 5213da08      Idx  2  length  4  -  B 154f6d51      Idx  3  length  4  -  B 1191ebc5      Idx  4  length  4  -  B 30ddb86      Idx  5  length  4  -  B 2c73bfb      Idx  6  length  2  -  B 6632dd29              But I like  Jon Skeets solution in https   stackoverflow com a 3760193 1237974 also  For maintainability in larger projects where not everyone are equally experienced in Regular expressions I would probably use Jons solution

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You can use substring from String class  handling exceptions  or from Apache lang commons  it handles exceptions for you   static String   substring String str  int start  int end     Put it inside a loop and you are good to go

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In case you want to split the string equally backwards  i e  from right to left  for example  to split 1010001111 to  10  1000  1111   here s the code           param s         the string to be split     param subLen    length of the equal-length substrings      param backwards true if the splitting is from right to left  false otherwise     return an array of equal-length substrings     throws ArithmeticException    by zero when subLen    0     public static String   split String s  int subLen  boolean backwards        assert s    null      int groups   s length     subLen    0   s length     subLen   s length     subLen   1      String   strs   new String groups       if  backwards            for  int i   0  i  lt  groups  i                  int beginIndex   s length   - subLen    i   1               int endIndex   beginIndex   subLen              if  beginIndex  lt  0                  beginIndex   0              strs groups - i - 1    s substring beginIndex  endIndex                   else           for  int i   0  i  lt  groups  i                  int beginIndex   subLen   i              int endIndex   beginIndex   subLen              if  endIndex  gt  s length                    endIndex   s length                strs i    s substring beginIndex  endIndex                       return strs

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If you re using Google s guava general-purpose libraries  and quite honestly  any new Java project probably should be   this is insanely trivial with the Splitter class   for  String substring   Splitter fixedLength 4  split inputString         doSomethingWith substring       and that s it  Easy as

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This is very easy with Google Guava   for final String token       Splitter          fixedLength 4           split  Thequickbrownfoxjumps         System out println token       Output   Theq uick brow nfox jump s   Or if you need the result as an array  you can use this code   String   tokens       Iterables toArray          Splitter              fixedLength 4               split  Thequickbrownfoxjumps            String class          Reference    Splitter fixedLength   Splitter split   Iterables toArray     Note  Splitter construction is shown inline above  but since Splitters are immutable and reusable  it s a good practice to store them in constants   private static final Splitter FOUR LETTERS   Splitter fixedLength 4       more code  for final String token   FOUR LETTERS split  Thequickbrownfoxjumps         System out println token

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A StringBuilder version  public static List lt String gt  getChunks String s  int chunkSize     List lt String gt  chunks   new ArrayList lt  gt      StringBuilder sb   new StringBuilder s    while   sb length     0                    chunks add sb substring 0  chunkSize       sb delete 0  chunkSize      return chunks

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Well  it s fairly easy to do this with simple arithmetic and string operations   public static List lt String gt  splitEqually String text  int size           Give the list the right capacity to start with  You could use an array        instead if you wanted      List lt String gt  ret   new ArrayList lt String gt   text length     size - 1    size        for  int start   0  start  lt  text length    start    size            ret add text substring start  Math min text length    start   size               return ret      I don t think it s really worth using a regex for this   EDIT  My reasoning for not using a regex    This doesn t use any of the real pattern matching of regexes  It s just counting  I suspect the above will be more efficient  although in most cases it won t matter If you need to use variable sizes in different places  you ve either got repetition or a helper function to build the regex itself based on a parameter - ick  The regex provided in another answer firstly didn t compile  invalid escaping   and then didn t work  My code worked first time  That s more a testament to the usability of regexes vs plain code  IMO

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Here is a one liner implementation using Java8 streams   String input    Thequickbrownfoxjumps   final AtomicInteger atomicInteger   new AtomicInteger 0   Collection lt String gt  result   input chars                                        mapToObj c - gt  String valueOf  char c                                         collect Collectors groupingBy c - gt  atomicInteger getAndIncrement     4                                                                  Collectors joining                                          values      It gives the following output    Theq  uick  brow  nfox  jump  s

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i use the following java 8 solution   public static List lt String gt  splitString final String string  final int chunkSize      final int numberOfChunks    string length     chunkSize - 1    chunkSize    return IntStream range 0  numberOfChunks                     mapToObj index - gt  string substring index   chunkSize  Math min  index   1    chunkSize  string length                         collect toList

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public static String   split String input  int length  throws IllegalArgumentException        if length    0    input    null          return new String 0        int lengthD   length   2       int size   input length        if size    0          return new String 0        int rep    int  Math ceil size   1d   length        ByteArrayInputStream stream   new ByteArrayInputStream input getBytes StandardCharsets UTF 16LE         String   out   new String rep       byte    buf   new byte lengthD        int d   0      for  int i   0  i  lt  rep  i               try               d   stream read buf             catch  IOException e                e printStackTrace                       if d    lengthD                        out i    new String buf 0 d  StandardCharsets UTF 16LE               continue                     out i    new String buf  StandardCharsets UTF 16LE             return out

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Test public void regexSplit         String source    Thequickbrownfoxjumps          define matcher  any char  min length 1  max length 4     Matcher matcher   Pattern compile    1 4    matcher source       List lt String gt  result   new ArrayList lt  gt         while  matcher find              result add source substring matcher start    matcher end                String   expected     Theq    uick    brow    nfox    jump    s        assertArrayEquals result toArray    expected

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Here s a one-liner version which uses Java 8 IntStream to determine the indexes of the slice beginnings   String x    Thequickbrownfoxjumps    String   result   IntStream                      iterate 0  i - gt  i   4                       limit  int  Math ceil x length     4 0                        mapToObj i - gt                          x substring i  Math min i   4  x length                                               toArray String    new

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public String   splitInParts String s  int partLength        int len   s length            Number of parts     int nparts    len   partLength - 1    partLength      String parts     new String nparts           Break into parts     int offset  0      int i   0      while  i  lt  nparts                parts i    s substring offset  Math min offset   partLength  len            offset    partLength          i               return parts

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import static java lang System exit     import java util Scanner     import Java util Arrays       public class string123    public static void main String   args        Scanner sc new Scanner System in       System out println  Enter String        String r sc nextLine        String   s new String 10       int len r length           System out println  Enter length Of Sub-string        int l sc nextInt        int last      int f 0      for int i 0  i             last  f l               if  last  gt  len  last len          s i  r substring f last           System out println s i           if  last  len break         f  f l              System out print Arrays tostring s             Result   Enter String  Thequickbrownfoxjumps  Enter length Of Sub-string  4     Theq   uick   brow   nfox   jump   s

[java] Split string to equal length substrings in Java

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