Java convert List String to a String

Question

JavaScript has Array join    js gt   Bill   Bob   Steve   join   and    Bill and Bob and Steve   Does Java have anything like this  I know I can cobble something up myself with StringBuilder   static public String join List lt String gt  list  String conjunction       StringBuilder sb   new StringBuilder       boolean first   true     for  String item   list             if  first           first   false        else          sb append conjunction         sb append item           return sb toString           but there s no point in doing this if something like it is already part of the JDK

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With a java 8 collector  this can be done with the following code   Arrays asList  Bill    Bob    Steve   stream    collect Collectors joining   and        Also  the simplest solution in java 8   String join   and     Bill    Bob    Steve      or  String join   and    Arrays asList  Bill    Bob    Steve

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Java 8 solution with java util StringJoiner  Java 8 has got a StringJoiner class  But you still need to write a bit of boilerplate  because it s Java   StringJoiner sj   new StringJoiner   and              String   names     Bill    Bob    Steve    for  String name   names       sj add name     System out println sj

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You can use this from Spring Framework s StringUtils  I know it s already been mentioned  but you can actually just take this code and it works immediately  without needing Spring for it      from https   github com spring-projects spring-framework blob master spring-core src main java org springframework util StringUtils java        Copyright 2002-2017 the original author or authors        Licensed under the Apache License  Version 2 0  the  License       you may not use this file except in compliance with the License     You may obtain a copy of the License at            http   www apache org licenses LICENSE-2 0       Unless required by applicable law or agreed to in writing  software    distributed under the License is distributed on an  AS IS  BASIS     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND  either express or implied     See the License for the specific language governing permissions and    limitations under the License      public class StringUtils       public static String collectionToDelimitedString Collection lt   gt  coll  String delim  String prefix  String suffix            if coll    null    coll isEmpty                  return                       StringBuilder sb   new StringBuilder            Iterator lt   gt  it   coll iterator            while  it hasNext                  sb append prefix  append it next    append suffix               if  it hasNext                      sb append delim                                   return sb toString

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Try this    java util Arrays toString anArray  replaceAll                             replaceFirst            replaceFirst

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Three possibilities in Java 8   List lt String gt  list   Arrays asList  Alice    Bob    Charlie    String result   String join   and    list    result   list stream   collect Collectors joining   and       result   list stream   reduce  t  u  - gt  t     and     u  orElse

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An orthodox way to achieve it  is by defining a new function   public static String join String joinStr  String    strings        if  strings    null    strings length    0            return           else if  strings length    1            return strings 0         else           StringBuilder sb   new StringBuilder strings length   1   strings 0  length             sb append strings 0            for  int i   1  i  lt  strings length  i                  sb append joinStr  append strings i                      return sb toString              Sample   String   array   new String      7  7  7    Bill    Bob    Steve             Bill     1 2 3    Apple               String joined  joined   join   and    7  7  7    Bill    Bob    Steve     Bill     1 2 3    Apple             joined   join   and    array      same result  System out println joined     Output      7  7  7 and Bill and Bob and Steve and  Bill  and 1 2 3 and Apple    and

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If you re using Eclipse Collections  formerly GS Collections   you can use the makeString   method   List lt String gt  list   Arrays asList  Bill    Bob    Steve     String string   ListAdapter adapt list  makeString   and      Assert assertEquals  Bill and Bob and Steve   string     If you can convert your List to an Eclipse Collections type  then you can get rid of the adapter   MutableList lt String gt  list   Lists mutable with  Bill    Bob    Steve    String string   list makeString   and       If you just want a comma separated string  you can use the version of makeString   that takes no parameters   Assert assertEquals       Bill  Bob  Steve        Lists mutable with  Bill    Bob    Steve   makeString       Note  I am a committer for Eclipse Collections

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With Java 8 you can do this without any third party library   If you want to join a Collection of Strings you can use the new String join   method   List lt String gt  list   Arrays asList  foo    bar    baz    String joined   String join   and    list       foo and bar and baz    If you have a Collection with another type than String you can use the Stream API with the joining Collector   List lt Person gt  list   Arrays asList    new Person  John    Smith      new Person  Anna    Martinez      new Person  Paul    Watson        String joinedFirstNames   list stream      map Person  getFirstName     collect Collectors joining             John  Anna  Paul    The StringJoiner class may also be useful

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No  there s no such convenience method in the standard Java API   Not surprisingly  Apache Commons provides such a thing in their StringUtils class in case you don t want to write it yourself

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You might want to try Apache Commons StringUtils join method   http   commons apache org lang api org apache commons lang StringUtils html join java util Iterator  java lang String   I ve found that Apache StringUtils picks up jdk s slack  -

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A fun way to do it with pure JDK  in one duty line   String   array   new String      Bill    Bob    Steve    Bill    1 2 3   Apple        String join     and     String joined   Arrays toString array  replaceAll       join           replaceAll                        System out println joined     Output      Bill and Bob and Steve and  Bill  and 1 2 3 and Apple        A not too perfect  amp  not too fun way   String   array   new String      7  7  7   Bill    Bob    Steve     Bill             1 2 3    Apple        String join     and     for  int i   0  i  lt  array length  i    array i    array i  replaceAll               String joined   Arrays toString array  replaceAll       join           replaceAll                      replaceAll                System out println joined     Output      7  7  7 and Bill and Bob and Steve and  Bill  and 1 2 3 and Apple

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Java 8 does bring the  Collectors joining CharSequence delimiter  CharSequence prefix  CharSequence suffix    method  that is nullsafe by using prefix   suffix for null values   It can be used in the following manner   String s   stringList stream   collect Collectors joining   and     prefix      suffix      The  Collectors joining CharSequence delimiter  method just calls joining delimiter          internally

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You can use the apache commons library which has a StringUtils class and a join method   Check this link  https   commons apache org proper commons-lang javadocs api 2 0 org apache commons lang StringUtils html  Note that the link above may become obsolete over time  in which case you can just search the web for  apache commons StringUtils   which should allow you to find the latest reference    referenced from this thread  Java equivalents of C  String Format   and String Join

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On Android you could use TextUtils class   TextUtils join   and    names

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Google s Guava API also has  join    although  as should be obvious with the other replies   Apache Commons is pretty much the standard here

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You can do this   String aToString   java util Arrays toString anArray      Do not need to do this if you are OK with     and     aToString   aToString substring 1  aToString length   - 1     Or a one-liner  only when you do not want     and       String aToString   java util Arrays toString anArray  substring 1  replaceAll               Hope this helps

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Not out of the box  but many libraries have similar   Commons Lang   org apache commons lang StringUtils join list  conjunction     Spring   org springframework util StringUtils collectionToDelimitedString list  conjunction

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EDIT  I also notice the  toString   underlying implementation issue  and about the element containing the separator but I thought I was being paranoid    Since I ve got two comments on that regard  I m changing my answer to   static String join  List lt String gt  list   String replacement          StringBuilder b   new StringBuilder        for  String item  list              b append  replacement   append  item              return b toString   substring  replacement length          Which looks pretty similar to the original question   So if you don t feel like adding the whole jar to your project you may use this    I think there s nothing wrong with your original code  Actually  the alternative that everyone s is suggesting looks almost the same   although it does a number of additional validations     Here it is  along with the  Apache 2 0 license   public static String join Iterator iterator  String separator           handle null  zero and one elements before building a buffer     if  iterator    null            return null            if   iterator hasNext              return EMPTY            Object first   iterator next        if   iterator hasNext              return ObjectUtils toString first                 two or more elements     StringBuffer buf   new StringBuffer 256      Java default is 16  probably too small     if  first    null            buf append first              while  iterator hasNext              if  separator    null                buf append separator                     Object obj   iterator next            if  obj    null                buf append obj                       return buf toString        Now we know  thank you open source

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I wrote this one  I use it for beans and exploit toString  so don t write Collection lt String gt     public static String join Collection lt   gt  col  String delim        StringBuilder sb   new StringBuilder        Iterator lt   gt  iter   col iterator        if  iter hasNext            sb append iter next   toString         while  iter hasNext              sb append delim           sb append iter next   toString               return sb toString        but Collection isn t supported by JSP  so for TLD I wrote   public static String join List lt   gt  list  String delim        int len   list size        if  len    0          return         StringBuilder sb   new StringBuilder list get 0  toString         for  int i   1  i  lt  len  i              sb append delim           sb append list get i  toString               return sb toString        and put to  tld file    lt  xml version  1 0  encoding  UTF-8   gt   lt taglib version  2 1  xmlns  http   java sun com xml ns javaee       lt function gt           lt name gt join lt  name gt           lt function-class gt com core util ReportUtil lt  function-class gt           lt function-signature gt java lang String join java util List  java lang String  lt  function-signature gt       lt  function gt   lt  taglib gt    and use it in JSP files as    lt   taglib prefix  funnyFmt  uri  tag com core util 2013 funnyFmt   gt    funnyFmt join books

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With java 1 8 stream can be used    import java util Arrays  import java util List  import java util stream Collectors  List lt String gt  list   Arrays asList  Bill   Bob   Steve    String str   list stream   collect Collectors joining   and

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Code you have is right way to do it if you want to do using JDK without any external libraries  There is no simple  one-liner  that you could use in JDK    If you can use external libs  I recommend that you look into org apache commons lang StringUtils class in Apache Commons library    An example of usage   List lt String gt  list   Arrays asList  Bill    Bob    Steve    String joinedResult   StringUtils join list    and

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All the references to Apache Commons are fine  and that is what most people use  but I think the Guava equivalent  Joiner  has a much nicer API   You can do the simple join case with  Joiner on   and    join names    but also easily deal with nulls   Joiner on   and    skipNulls   join names     or  Joiner on   and    useForNull   unknown    join names     and  useful enough as far as I m concerned to use it in preference to commons-lang   the ability to deal with Maps   Map lt String  Integer gt  ages          String foo   Joiner on       withKeyValueSeparator   is    join ages      Outputs     Bill is 25  Joe is 30  Betty is 35   which is extremely useful for debugging etc

[java] Java: convert List<String> to a String

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