Remove last character of a StringBuilder

Question

When you have to loop through a collection and make a string of each data separated by a delimiter  you always end up with an extra delimiter at the end  e g   for  String serverId   serverIds      sb append serverId      sb append           Gives something like   serverId 1  serverId 2  serverId 3   I would like to delete the last character in the StringBuilder  without converting it because I still need it after this loop

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As of Java 8  the String class has a static method join  The first argument is a string that you want between each pair of strings  and the second is an Iterable lt CharSequence gt   which are both interfaces  so something like List lt String gt  works  So you can just do this   String join      serverIds     Also in Java 8  you could use the new StringJoiner class  for scenarios where you want to start constructing the string before you have the full list of elements to put in it

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I personally like to append a backspace character  or more for longer  delimiter   at the end   for String serverId   serverIds        sb append serverId       sb append          sb append   b      Note that it has problems    how  b is displayed depends on the environment  the length   of the String content might be different from the length of  visibile  characters   When  b looks OK and the length doesn t matter such as logging to a console  this seems good enough to me

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Another simple solution is   sb setLength sb length   - 1       A more complicated solution   The above solution assumes that sb length    gt  0     i e  there is a  last character  to remove   If you can t make that assumption  and or you can t deal with the exception that would ensue if the assumption is incorrect  then check the StringBuilder s length first  e g      Readable version if  sb length    gt  0       sb setLength sb length   - 1       or      Concise but harder-to-read version of the above  sb setLength Math max sb length   - 1  0

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stringBuilder Remove stringBuilder Length - 1  1

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Here is another solution   for String serverId   serverIds       sb append          sb append serverId       String resultingString       if   sb length    gt  1         resultingString   sb substring 1

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since you know the character you want to remove you can use this sb TrimEnd  quot   quot

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Yet another alternative   public String join Collection lt String gt  collection  String seperator        if  collection isEmpty    return          Iterator lt String gt  iter   collection iterator        StringBuilder sb   new StringBuilder iter next         while  iter hasNext              sb append seperator           sb append iter next                return sb toString

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With Java-8 you can use static method of String class   String join CharSequence delimiter Iterable lt   extends CharSequence gt  elements      public class Test        public static void main String   args             List lt String gt  names   new ArrayList lt  gt             names add  James            names add  Harry            names add  Roy            System out println String join      names              OUTPUT  James Harry Roy

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I am doing something like below       StringBuilder stringBuilder   new StringBuilder        for  int i   0  i  lt  value length  i              stringBuilder append values i            if  value length-1                stringBuilder append

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StringBuilder sb   new StringBuilder    sb append  abcdef    sb deleteCharAt sb length   - 1   assertEquals  abcde  sb toString        true

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Just get the position of the last character occurrence   for String serverId   serverIds     sb append serverId    sb append         sb deleteCharAt sb lastIndexOf          Since lastIndexOf will perform a reverse search  and you know that it will find at the first try  performance won t be an issue here   EDIT  Since I keep getting ups on my answer  thanks folks    it is worth regarding that   On Java 8 onward it would just be more legible and explicit to use StringJoiner  It has one method for a simple separator  and an overload for prefix and suffix   Examples taken from here  example  Example using simple separator        StringJoiner mystring   new StringJoiner  -                Joining multiple strings by using add   method       mystring add  Logan          mystring add  Magneto          mystring add  Rogue          mystring add  Storm           System out println mystring      Output      Logan-Magneto-Rogue-Storm   Example with suffix and prefix        StringJoiner mystring   new StringJoiner                             Joining multiple strings by using add   method       mystring add  Negan          mystring add  Rick          mystring add  Maggie          mystring add  Daryl           System out println mystring      Output      Negan Rick Maggie Daryl

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In this case   sb setLength sb length   - 1     is preferable as it just assign the last value to   0  whereas deleting last character does System arraycopy

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Another alternative  for String serverId   serverIds       sb append          sb append serverId      sb deleteCharAt 0

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Others have pointed out the deleteCharAt method  but here s another alternative approach   String prefix       for  String serverId   serverIds      sb append prefix     prefix          sb append serverId       Alternatively  use the Joiner class from Guava     As of Java 8  StringJoiner is part of the standard JRE

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if sb length    gt  0       sb deleteCharAt sb length   - 1

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Alternatively   StringBuilder result   new StringBuilder    for String string   collection        result append string       result append         return result substring 0  result length   - 1

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To avoid reinit affect performance  of  prefix use TextUtils isEmpty               String prefix                   for  String item   list                    sb append prefix                   if  TextUtils isEmpty prefix                       prefix                        sb append item

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You may try to use  Joiner  class instead of removing the last character from your generated text                   List lt String gt  textList   new ArrayList lt  gt                     textList add  text1                    textList add  text2                    textList add  text3                     Joiner joiner   Joiner on      useForNull  null                    String output   joiner join textList                     output    text1 text2 text3

[java] Remove last character of a StringBuilder?

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