The most sophisticated way for creating comma-separated Strings from a Collection Array List

Question

During my work with databases I noticed that I write query strings and in this strings I have to put several restrictions in the where-clause from a list array collection  Should look like this   select   from customer  where customer id in  34  26       2     You can simplify this by reducing this to the question that you have collection of strings and want to create a comma-separated list of this strings in just one string   My approach I have used so far is something like that   String result       boolean first   true  for String string   collectionOfStrings        if first            result  string          first false        else           result      string            But this is as you can see very ugly  You cannot see what happens there on the first look  especially when the constructed strings  like every SQL query  is getting complicated   What is your  more  elegant way

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I ve just checked-in a test for my library dollar    Test public void join         List lt Integer gt  list   Arrays asList 1  2  3  4  5       String string     list  join           it create a fluent wrapper around lists arrays strings etc using only one static import      NB   using ranges the previous list can be re-writed as   1  5  join

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You may be able to use LINQ  to SQL   and you may be able to make use of the Dynamic Query LINQ sample from MS  http   weblogs asp net scottgu archive 2008 01 07 dynamic-linq-part-1-using-the-linq-dynamic-query-library aspx

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The Most easier way in android for convert List to Comma separated String is By useing android text TextUtils   ArrayList lt String gt Myli   new ArrayList lt String gt      String ArayCommase android text TextUtils join      Myli

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You could try  List collections   Arrays asList 34  26         2   String asString   collection toString       justValues    34  26       2  String justValues   asString substring 1  asString length  -1

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Use the Google Guava API s join method   Joiner on      join collectionOfStrings

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In Android you should use this   TextUtils join     collectionOfStrings toArray

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Note  This answers was good when it was written 11 years ago  but now there are far better options to do this more cleanly in a single line  both using only Java built-in classes or using a utility library  See other answers below     Since strings are immutable  you may want to use the StringBuilder class if you re going to alter the String in the code   The StringBuilder class can be seen as a mutable String object which allocates more memory when its content is altered   The original suggestion in the question can be written even more clearly and efficiently  by taking care of the redundant trailing comma       StringBuilder result   new StringBuilder        for String string   collectionOfStrings            result append string           result append                 return result length    gt  0   result substring 0  result length   - 1

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Another option  based on what I see here  with slight modifications    public static String toString int   numbers        StringBuilder res   new StringBuilder        for  int number   numbers            if  res length      0                res append                         res append number             return res toString

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if you have an array you can do   Arrays asList parameters  toString

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There s a lot of manual solutions to this  but I wanted to reiterate and update Julie s answer above  Use google collections Joiner class   Joiner on       join 34  26       2    It handles var args  iterables and arrays and properly handles separators of more than one char  unlike gimmel s answer   It will also handle null values in your list if you need it to

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Just another method to deal with this problem  Not the most short  but it is efficient and gets the job done          Creates a comma-separated list of values from given collection          param  lt T gt  Value type      param values Value collection      return Comma-separated String of values      public  lt T gt  String toParameterList Collection lt T gt  values       if  values    null    values isEmpty            return        Depending on how you want to deal with this case            StringBuilder result   new StringBuilder       Iterator lt T gt  i   values iterator       result append i next   toString        while  i hasNext            result append      append i next   toString             return result toString

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java util List lt String gt  lista   new java util ArrayList lt String gt     lista add  Hola    lista add  Julio    System out println lista toString   replace          replace                Hola  Julio

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I m not sure how  sophisticated  this is  but it s certainly a bit shorter  It will work with various different types of collection e g  Set lt Integer gt   List lt String gt   etc   public static final String toSqlList Collection lt   gt  values         String collectionString   values toString            Convert the square brackets produced by Collection toString   to round brackets used by SQL     return       collectionString substring 1  collectionString length   - 1             Exercise for reader  modify this method so that it correctly handles a null empty collection

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You may be able to use LINQ  to SQL   and you may be able to make use of the Dynamic Query LINQ sample from MS  http   weblogs asp net scottgu archive 2008 01 07 dynamic-linq-part-1-using-the-linq-dynamic-query-library aspx

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Just another method to deal with this problem  Not the most short  but it is efficient and gets the job done          Creates a comma-separated list of values from given collection          param  lt T gt  Value type      param values Value collection      return Comma-separated String of values      public  lt T gt  String toParameterList Collection lt T gt  values       if  values    null    values isEmpty            return        Depending on how you want to deal with this case            StringBuilder result   new StringBuilder       Iterator lt T gt  i   values iterator       result append i next   toString        while  i hasNext            result append      append i next   toString             return result toString

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In case someone stumbled over this in more recent times  I have added a simple variation using Java 8 reduce    It also includes some of the already mentioned solutions by others   import java util Arrays  import java util List   import org apache commons lang StringUtils       import com google common base Joiner   public class Dummy     public static void main String   args         List lt String gt  strings   Arrays asList  abc    de    fg        String commaSeparated   strings          stream            reduce  s1  s2  - gt   return s1         s2              get         System out println commaSeparated        System out println Joiner on      join strings         System out println StringUtils join strings

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What makes the code ugly is the special-handling for the first case   Most of the lines in this small snippet are devoted  not to doing the code s routine job  but to handling that special case   And that s what alternatives like gimel s solve  by moving the special handling outside the loop   There is one special case  well  you could see both start and end as special cases - but only one of them needs to be treated specially   so handling it inside the loop is unnecessarily complicated

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If you use Spring  you can do   StringUtils arrayToCommaDelimitedString      collectionOfStrings toArray        package org springframework util

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String commaSeparatedNames   namesList toString   replaceAll                           replace   or   or blank      The string representation consists of a list of the collection s   elements in the order they are returned by its iterator  enclosed in   square brackets         Adjacent elements are separated by the   characters       comma and space        AbstractCollection javadoc

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Just another method to deal with this problem  Not the most short  but it is efficient and gets the job done          Creates a comma-separated list of values from given collection          param  lt T gt  Value type      param values Value collection      return Comma-separated String of values      public  lt T gt  String toParameterList Collection lt T gt  values       if  values    null    values isEmpty            return        Depending on how you want to deal with this case            StringBuilder result   new StringBuilder       Iterator lt T gt  i   values iterator       result append i next   toString        while  i hasNext            result append      append i next   toString             return result toString

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I ve just checked-in a test for my library dollar    Test public void join         List lt Integer gt  list   Arrays asList 1  2  3  4  5       String string     list  join           it create a fluent wrapper around lists arrays strings etc using only one static import      NB   using ranges the previous list can be re-writed as   1  5  join

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String commaSeparatedNames   namesList toString   replaceAll                           replace   or   or blank      The string representation consists of a list of the collection s   elements in the order they are returned by its iterator  enclosed in   square brackets         Adjacent elements are separated by the   characters       comma and space        AbstractCollection javadoc

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I found the iterator idiom elegant  because it has a test for more elements  ommited null empty test for brevity    public static String convert List lt String gt  list        String res           for  Iterator lt String gt  iterator   list iterator    iterator hasNext               res    iterator next      iterator hasNext                          return res

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I think it s not a good idea contruct the sql concatenating the where clause values like you are doing    SELECT     FROM     WHERE ID IN  value1  value2     valueN    Where valueX comes from a list of Strings    First  if you are comparing Strings they must be quoted  an this it isn t trivial if the Strings could have a quote inside    Second  if the values comes from the user or other system  then a SQL injection attack is possible   It s a lot more verbose but what you should do is create a String like this   SELECT     FROM     WHERE ID IN                and then bind the variables with Statement setString nParameter parameterValue

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This will be the shortest solution so far  except of using Guava or Apache Commons  String res       for  String i   values        res    res isEmpty     i       i      Good with 0 1 and n element list  But you ll need to check for null list  I use this in GWT  so I m good without StringBuilder there  And for short lists with just couple of elements its ok too elsewhere

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While I think your best bet is to use Joiner from Guava  if I were to code it by hand I find this approach more elegant that the  first  flag or chopping the last comma off     private String commas Iterable lt String gt  strings        StringBuilder buffer   new StringBuilder        Iterator lt String gt  it   strings iterator        if  it hasNext              buffer append it next             while  it hasNext                  buffer append                   buffer append it next                          return buffer toString

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While I think your best bet is to use Joiner from Guava  if I were to code it by hand I find this approach more elegant that the  first  flag or chopping the last comma off     private String commas Iterable lt String gt  strings        StringBuilder buffer   new StringBuilder        Iterator lt String gt  it   strings iterator        if  it hasNext              buffer append it next             while  it hasNext                  buffer append                   buffer append it next                          return buffer toString

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Use the Google Guava API s join method   Joiner on      join collectionOfStrings

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In Android you should use this   TextUtils join     collectionOfStrings toArray

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Another option  based on what I see here  with slight modifications    public static String toString int   numbers        StringBuilder res   new StringBuilder        for  int number   numbers            if  res length      0                res append                         res append number             return res toString

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If you use Spring  you can do   StringUtils arrayToCommaDelimitedString      collectionOfStrings toArray        package org springframework util

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Here s an incredibly generic version that I ve built from a combination of the previous suggestions   public static  lt T gt  String buildCommaSeparatedString Collection lt T gt  values        if  values  null    values isEmpty    return         StringBuilder result   new StringBuilder        for  T val   values            result append val           result append                 return result substring 0  result length   - 1

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The way I write that loop is   StringBuilder buff   new StringBuilder    String sep       for  String str   strs        buff append sep       buff append str       sep          return buff toString      Don t worry about the performance of sep  An assignment is very fast  Hotspot tends to peel off the first iteration of a loop anyway  as it often has to deal with oddities such as null and mono bimorphic inlining checks    If you use it lots  more than once   put it in a shared method   There is another question on stackoverflow dealing with how to insert a list of ids into an SQL statement

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Since Java 8  you can use    String String join CharSequence delimiter  CharSequence    elements  String String join CharSequence delimiter  Iterable lt   extends CharSequence gt  elements  If you want to take non-Strings and join them to a String  you can use Collectors joining CharSequence delimiter   e g    String joined   anyCollection stream   map Object  toString  collect Collectors joining

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The nice thing about the IN expression is that if you have repeated values  it does not change the result   So  just duplicate the first item and process the entire list   This assumes that there is at least one item in the list   If there are no items  I d suggest checking for that first and then not executing the SQL at all   This will do the trick  is obvious in what it is doing and does not rely on any external libraries   StringBuffer inString   new StringBuffer listOfIDs get 0  toString     for  Long currentID   listOfIDs      inString append      append currentID

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java util List lt String gt  lista   new java util ArrayList lt String gt     lista add  Hola    lista add  Julio    System out println lista toString   replace          replace                Hola  Julio

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I m not sure how  sophisticated  this is  but it s certainly a bit shorter  It will work with various different types of collection e g  Set lt Integer gt   List lt String gt   etc   public static final String toSqlList Collection lt   gt  values         String collectionString   values toString            Convert the square brackets produced by Collection toString   to round brackets used by SQL     return       collectionString substring 1  collectionString length   - 1             Exercise for reader  modify this method so that it correctly handles a null empty collection

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I m not sure how  sophisticated  this is  but it s certainly a bit shorter  It will work with various different types of collection e g  Set lt Integer gt   List lt String gt   etc   public static final String toSqlList Collection lt   gt  values         String collectionString   values toString            Convert the square brackets produced by Collection toString   to round brackets used by SQL     return       collectionString substring 1  collectionString length   - 1             Exercise for reader  modify this method so that it correctly handles a null empty collection

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There are some third-party Java libraries that provide string join method  but you probably don t want to start using a library just for something simple like that  I would just create a helper method like this  which I think is a bit better than your version  It uses StringBuffer  which will be more efficient if you need to join many strings  and it works on a collection of any type   public static  lt T gt  String join Collection lt T gt  values        StringBuffer ret   new StringBuffer        for  T value   values                if  ret length    gt  0  ret append               ret append value             return ret toString        Another suggestion with using Collection toString   is shorter  but that relies on Collection toString   returning a string in a very specific format  which I would personally not want to rely on

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This will be the shortest solution so far  except of using Guava or Apache Commons  String res       for  String i   values        res    res isEmpty     i       i      Good with 0 1 and n element list  But you ll need to check for null list  I use this in GWT  so I m good without StringBuilder there  And for short lists with just couple of elements its ok too elsewhere

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There s a lot of manual solutions to this  but I wanted to reiterate and update Julie s answer above  Use google collections Joiner class   Joiner on       join 34  26       2    It handles var args  iterables and arrays and properly handles separators of more than one char  unlike gimmel s answer   It will also handle null values in your list if you need it to

User · Answer

Note  This answers was good when it was written 11 years ago  but now there are far better options to do this more cleanly in a single line  both using only Java built-in classes or using a utility library  See other answers below     Since strings are immutable  you may want to use the StringBuilder class if you re going to alter the String in the code   The StringBuilder class can be seen as a mutable String object which allocates more memory when its content is altered   The original suggestion in the question can be written even more clearly and efficiently  by taking care of the redundant trailing comma       StringBuilder result   new StringBuilder        for String string   collectionOfStrings            result append string           result append                 return result length    gt  0   result substring 0  result length   - 1

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What makes the code ugly is the special-handling for the first case   Most of the lines in this small snippet are devoted  not to doing the code s routine job  but to handling that special case   And that s what alternatives like gimel s solve  by moving the special handling outside the loop   There is one special case  well  you could see both start and end as special cases - but only one of them needs to be treated specially   so handling it inside the loop is unnecessarily complicated

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I just looked at code that did this today   This is a variation on AviewAnew s answer   collectionOfStrings      source string collection     String csList   StringUtils join collectionOfStrings toArray            The StringUtils    lt -- commons lang 2 x  or commons lang 3 x link  we used is from Apache Commons

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The nice thing about the IN expression is that if you have repeated values  it does not change the result   So  just duplicate the first item and process the entire list   This assumes that there is at least one item in the list   If there are no items  I d suggest checking for that first and then not executing the SQL at all   This will do the trick  is obvious in what it is doing and does not rely on any external libraries   StringBuffer inString   new StringBuffer listOfIDs get 0  toString     for  Long currentID   listOfIDs      inString append      append currentID

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I think it s not a good idea contruct the sql concatenating the where clause values like you are doing    SELECT     FROM     WHERE ID IN  value1  value2     valueN    Where valueX comes from a list of Strings    First  if you are comparing Strings they must be quoted  an this it isn t trivial if the Strings could have a quote inside    Second  if the values comes from the user or other system  then a SQL injection attack is possible   It s a lot more verbose but what you should do is create a String like this   SELECT     FROM     WHERE ID IN                and then bind the variables with Statement setString nParameter parameterValue

User · Answer

Here s an incredibly generic version that I ve built from a combination of the previous suggestions   public static  lt T gt  String buildCommaSeparatedString Collection lt T gt  values        if  values  null    values isEmpty    return         StringBuilder result   new StringBuilder        for  T val   values            result append val           result append                 return result substring 0  result length   - 1

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I just looked at code that did this today   This is a variation on AviewAnew s answer   collectionOfStrings      source string collection     String csList   StringUtils join collectionOfStrings toArray            The StringUtils    lt -- commons lang 2 x  or commons lang 3 x link  we used is from Apache Commons

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You may be able to use LINQ  to SQL   and you may be able to make use of the Dynamic Query LINQ sample from MS  http   weblogs asp net scottgu archive 2008 01 07 dynamic-linq-part-1-using-the-linq-dynamic-query-library aspx

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There are some third-party Java libraries that provide string join method  but you probably don t want to start using a library just for something simple like that  I would just create a helper method like this  which I think is a bit better than your version  It uses StringBuffer  which will be more efficient if you need to join many strings  and it works on a collection of any type   public static  lt T gt  String join Collection lt T gt  values        StringBuffer ret   new StringBuffer        for  T value   values                if  ret length    gt  0  ret append               ret append value             return ret toString        Another suggestion with using Collection toString   is shorter  but that relies on Collection toString   returning a string in a very specific format  which I would personally not want to rely on

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There are some third-party Java libraries that provide string join method  but you probably don t want to start using a library just for something simple like that  I would just create a helper method like this  which I think is a bit better than your version  It uses StringBuffer  which will be more efficient if you need to join many strings  and it works on a collection of any type   public static  lt T gt  String join Collection lt T gt  values        StringBuffer ret   new StringBuffer        for  T value   values                if  ret length    gt  0  ret append               ret append value             return ret toString        Another suggestion with using Collection toString   is shorter  but that relies on Collection toString   returning a string in a very specific format  which I would personally not want to rely on

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Note  This answers was good when it was written 11 years ago  but now there are far better options to do this more cleanly in a single line  both using only Java built-in classes or using a utility library  See other answers below     Since strings are immutable  you may want to use the StringBuilder class if you re going to alter the String in the code   The StringBuilder class can be seen as a mutable String object which allocates more memory when its content is altered   The original suggestion in the question can be written even more clearly and efficiently  by taking care of the redundant trailing comma       StringBuilder result   new StringBuilder        for String string   collectionOfStrings            result append string           result append                 return result length    gt  0   result substring 0  result length   - 1

User · Answer

I found the iterator idiom elegant  because it has a test for more elements  ommited null empty test for brevity    public static String convert List lt String gt  list        String res           for  Iterator lt String gt  iterator   list iterator    iterator hasNext               res    iterator next      iterator hasNext                          return res

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You could try  List collections   Arrays asList 34  26         2   String asString   collection toString       justValues    34  26       2  String justValues   asString substring 1  asString length  -1

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Join  methods  are available in Arrays and the classes that extend AbstractCollections but doesn t override toString   method  like virtually all collections in java util    For instance   String s  java util Arrays toString collectionOfStrings toArray     s   s substing 1  s length  -1        are guaranteed to be there     That s quite weird way since it works only for numbers alike data SQL wise

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There is an easy way  You can get your result in a single line    String memberIdsModifiedForQuery   memberIds toString   replace           replace              To get complete idea check the code below   public static void main String   args                   List lt Integer gt memberIds new ArrayList lt Integer gt        This contain member ids we want to process           adding some sample values for example         memberIds add 3            memberIds add 4           memberIds add 2           String memberIdsModifiedForQuery   memberIds toString   replace           replace              here you will get  3 4 5  That you can directly use in query         System out println memberIdsModifiedForQuery           String exampleQuery  select   from customer where customer id in   memberIdsModifiedForQuery

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The Most easier way in android for convert List to Comma separated String is By useing android text TextUtils   ArrayList lt String gt Myli   new ArrayList lt String gt      String ArayCommase android text TextUtils join      Myli

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I found the iterator idiom elegant  because it has a test for more elements  ommited null empty test for brevity    public static String convert List lt String gt  list        String res           for  Iterator lt String gt  iterator   list iterator    iterator hasNext               res    iterator next      iterator hasNext                          return res

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List lt String gt  collectionOfStrings      List of string to concat String csvStrings   StringUtils collectionToDelimitedString collectionOfStrings          StringUtils from springframeowrk spring-core

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List token new ArrayList result   final StringBuilder builder   new StringBuilder         for  int i  0  i  lt  tokens size    i             builder append tokens get i            if i    tokens size  -1               builder append TOKEN DELIMITER                     builder toString

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I think it s not a good idea contruct the sql concatenating the where clause values like you are doing    SELECT     FROM     WHERE ID IN  value1  value2     valueN    Where valueX comes from a list of Strings    First  if you are comparing Strings they must be quoted  an this it isn t trivial if the Strings could have a quote inside    Second  if the values comes from the user or other system  then a SQL injection attack is possible   It s a lot more verbose but what you should do is create a String like this   SELECT     FROM     WHERE ID IN                and then bind the variables with Statement setString nParameter parameterValue

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The way I write that loop is   StringBuilder buff   new StringBuilder    String sep       for  String str   strs        buff append sep       buff append str       sep          return buff toString      Don t worry about the performance of sep  An assignment is very fast  Hotspot tends to peel off the first iteration of a loop anyway  as it often has to deal with oddities such as null and mono bimorphic inlining checks    If you use it lots  more than once   put it in a shared method   There is another question on stackoverflow dealing with how to insert a list of ids into an SQL statement

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There is an easy way  You can get your result in a single line    String memberIdsModifiedForQuery   memberIds toString   replace           replace              To get complete idea check the code below   public static void main String   args                   List lt Integer gt memberIds new ArrayList lt Integer gt        This contain member ids we want to process           adding some sample values for example         memberIds add 3            memberIds add 4           memberIds add 2           String memberIdsModifiedForQuery   memberIds toString   replace           replace              here you will get  3 4 5  That you can directly use in query         System out println memberIdsModifiedForQuery           String exampleQuery  select   from customer where customer id in   memberIdsModifiedForQuery

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The way I write that loop is   StringBuilder buff   new StringBuilder    String sep       for  String str   strs        buff append sep       buff append str       sep          return buff toString      Don t worry about the performance of sep  An assignment is very fast  Hotspot tends to peel off the first iteration of a loop anyway  as it often has to deal with oddities such as null and mono bimorphic inlining checks    If you use it lots  more than once   put it in a shared method   There is another question on stackoverflow dealing with how to insert a list of ids into an SQL statement

User · Answer

There are some third-party Java libraries that provide string join method  but you probably don t want to start using a library just for something simple like that  I would just create a helper method like this  which I think is a bit better than your version  It uses StringBuffer  which will be more efficient if you need to join many strings  and it works on a collection of any type   public static  lt T gt  String join Collection lt T gt  values        StringBuffer ret   new StringBuffer        for  T value   values                if  ret length    gt  0  ret append               ret append value             return ret toString        Another suggestion with using Collection toString   is shorter  but that relies on Collection toString   returning a string in a very specific format  which I would personally not want to rely on

User · Answer

Use the Google Guava API s join method   Joiner on      join collectionOfStrings

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In case someone stumbled over this in more recent times  I have added a simple variation using Java 8 reduce    It also includes some of the already mentioned solutions by others   import java util Arrays  import java util List   import org apache commons lang StringUtils       import com google common base Joiner   public class Dummy     public static void main String   args         List lt String gt  strings   Arrays asList  abc    de    fg        String commaSeparated   strings          stream            reduce  s1  s2  - gt   return s1         s2              get         System out println commaSeparated        System out println Joiner on      join strings         System out println StringUtils join strings

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The way I write that loop is   StringBuilder buff   new StringBuilder    String sep       for  String str   strs        buff append sep       buff append str       sep          return buff toString      Don t worry about the performance of sep  An assignment is very fast  Hotspot tends to peel off the first iteration of a loop anyway  as it often has to deal with oddities such as null and mono bimorphic inlining checks    If you use it lots  more than once   put it in a shared method   There is another question on stackoverflow dealing with how to insert a list of ids into an SQL statement

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String join       collectionOfStrings    available in the Java8 api   alternative to  without the need to add a google guava dependency    Joiner on      join collectionOfStrings

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Since Java 8  you can use    String String join CharSequence delimiter  CharSequence    elements  String String join CharSequence delimiter  Iterable lt   extends CharSequence gt  elements  If you want to take non-Strings and join them to a String  you can use Collectors joining CharSequence delimiter   e g    String joined   anyCollection stream   map Object  toString  collect Collectors joining

User · Answer

You may be able to use LINQ  to SQL   and you may be able to make use of the Dynamic Query LINQ sample from MS  http   weblogs asp net scottgu archive 2008 01 07 dynamic-linq-part-1-using-the-linq-dynamic-query-library aspx

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I found the iterator idiom elegant  because it has a test for more elements  ommited null empty test for brevity    public static String convert List lt String gt  list        String res           for  Iterator lt String gt  iterator   list iterator    iterator hasNext               res    iterator next      iterator hasNext                          return res

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Join  methods  are available in Arrays and the classes that extend AbstractCollections but doesn t override toString   method  like virtually all collections in java util    For instance   String s  java util Arrays toString collectionOfStrings toArray     s   s substing 1  s length  -1        are guaranteed to be there     That s quite weird way since it works only for numbers alike data SQL wise

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if you have an array you can do   Arrays asList parameters  toString

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List lt String gt  collectionOfStrings      List of string to concat String csvStrings   StringUtils collectionToDelimitedString collectionOfStrings          StringUtils from springframeowrk spring-core

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Use the Google Guava API s join method   Joiner on      join collectionOfStrings

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I think it s not a good idea contruct the sql concatenating the where clause values like you are doing    SELECT     FROM     WHERE ID IN  value1  value2     valueN    Where valueX comes from a list of Strings    First  if you are comparing Strings they must be quoted  an this it isn t trivial if the Strings could have a quote inside    Second  if the values comes from the user or other system  then a SQL injection attack is possible   It s a lot more verbose but what you should do is create a String like this   SELECT     FROM     WHERE ID IN                and then bind the variables with Statement setString nParameter parameterValue

User · Answer

Just another method to deal with this problem  Not the most short  but it is efficient and gets the job done          Creates a comma-separated list of values from given collection          param  lt T gt  Value type      param values Value collection      return Comma-separated String of values      public  lt T gt  String toParameterList Collection lt T gt  values       if  values    null    values isEmpty            return        Depending on how you want to deal with this case            StringBuilder result   new StringBuilder       Iterator lt T gt  i   values iterator       result append i next   toString        while  i hasNext            result append      append i next   toString             return result toString

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I just looked at code that did this today   This is a variation on AviewAnew s answer   collectionOfStrings      source string collection     String csList   StringUtils join collectionOfStrings toArray            The StringUtils    lt -- commons lang 2 x  or commons lang 3 x link  we used is from Apache Commons

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I just looked at code that did this today   This is a variation on AviewAnew s answer   collectionOfStrings      source string collection     String csList   StringUtils join collectionOfStrings toArray            The StringUtils    lt -- commons lang 2 x  or commons lang 3 x link  we used is from Apache Commons

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Note  This answers was good when it was written 11 years ago  but now there are far better options to do this more cleanly in a single line  both using only Java built-in classes or using a utility library  See other answers below     Since strings are immutable  you may want to use the StringBuilder class if you re going to alter the String in the code   The StringBuilder class can be seen as a mutable String object which allocates more memory when its content is altered   The original suggestion in the question can be written even more clearly and efficiently  by taking care of the redundant trailing comma       StringBuilder result   new StringBuilder        for String string   collectionOfStrings            result append string           result append                 return result length    gt  0   result substring 0  result length   - 1

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String join       collectionOfStrings    available in the Java8 api   alternative to  without the need to add a google guava dependency    Joiner on      join collectionOfStrings

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List token new ArrayList result   final StringBuilder builder   new StringBuilder         for  int i  0  i  lt  tokens size    i             builder append tokens get i            if i    tokens size  -1               builder append TOKEN DELIMITER                     builder toString

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I m not sure how  sophisticated  this is  but it s certainly a bit shorter  It will work with various different types of collection e g  Set lt Integer gt   List lt String gt   etc   public static final String toSqlList Collection lt   gt  values         String collectionString   values toString            Convert the square brackets produced by Collection toString   to round brackets used by SQL     return       collectionString substring 1  collectionString length   - 1             Exercise for reader  modify this method so that it correctly handles a null empty collection

[java] The most sophisticated way for creating comma-separated Strings from a Collection/Array/List?

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