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

User · Answer

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)

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

stringBuilder Remove stringBuilder Length - 1  1

User · Answer

if sb length    gt  0       sb deleteCharAt sb length   - 1

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

[java] Remove last character of a StringBuilder?

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