A method to reverse effect of java String split

Question

I am looking for a method to combine an array of strings into a delimited String  An opposite to split     Wanted to ask the forum before I try writing my own  since the JDK has everything

User · Answer

There s no method in the JDK for this that I m aware of  Apache Commons Lang has various overloaded join   methods in the StringUtils class that do what you want

User · Answer

I wrote this one   public static String join Collection lt String gt  col  String delim        StringBuilder sb   new StringBuilder        Iterator lt String gt  iter   col iterator        if  iter hasNext            sb append iter next         while  iter hasNext              sb append delim           sb append iter next               return sb toString        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

User · Answer

You can sneak this functionality out of the Arrays utility package  import java util Arrays          String delim    quot   quot               csv record    quot Field0 Field1 Field2 quot               fields     csv record split delim        String rebuilt record   Arrays toString fields               replace  quot    quot   delim               replaceAll  quot          quot    quot  quot

User · Answer

I got the following example here     7  Join Strings using separator  gt  gt  gt AB   CD   EF       import org apache commons lang StringUtils   public class StringUtilsTrial     public static void main String   args            Join all Strings in the Array into a Single String  separated by         System out println  7  Join Strings using separator  gt  gt  gt             StringUtils join new String      AB    CD    EF

User · Answer

Below code gives a basic idea  This is not best solution though   public static String splitJoin String sourceStr  String delim boolean trim boolean ignoreEmpty       return join Arrays asList sourceStr split delim    delim  ignoreEmpty       public static String join List lt   gt  list  String delim  boolean ignoreEmpty        int len   list size        if  len    0          return         StringBuilder sb   new StringBuilder list get 0  toString         for  int i   1  i  lt  len  i              if  ignoreEmpty  amp  amp   StringUtils isBlank list get i  toString                   sb append delim               sb append list get i  toString   trim                         return sb toString

User · Answer

If you have an int    Arrays toString   is the easiest way

User · Answer

I like this better   public String join Collection lt String gt  strCollection  String delimiter        String joined           int noOfItems   0      for  String item   strCollection            joined    item          if    noOfItems  lt  strCollection size                joined    delimiter            return joined      It is the neatest solution I have found so far   Don t worry about the use of raw String objects instead of StringBuilder  Modern Java compilers use StringBuilder anyway  but this code is more readable

User · Answer

Since JDK8 I love Streams and Lambdas a lot  so I would suggest   public static String join  String delimiter  String   array         return Arrays asList  array   stream   collect  Collectors joining  delimiter

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Google also provides a joiner class in their Google Collections library   Joiner API  Google Collections

User · Answer

If you use jdk8 see  Nathaniel Johnson s answer as that is better   I think that many of the answer here are complex or not easily read  With branch prediction so efficient why you simply not use a if statement   public static String join List lt String gt  fooList        if  fooList isEmpty    return          StringBuilder sb   null       for  String element   fooList             if  sb    null                sb   new StringBuilder              else               sb append                           sb append element             return sb toString        Something that should be mentioned is that Apache uses a simple for loop with an if statement inside it like this  it uses an array as its index to know the first element   and openjdk 8 does the same but in separated methods calls instead of a simple loop

User · Answer

For Android  in android text TextUtils there are methods   public static String join  CharSequence delimiter  Iterable tokens  public static String join  CharSequence delimiter  Object   tokens    Returns a string containing the tokens joined by delimiters   tokens --  an array objects to be joined  Strings will be formed from the objects by calling object toString

User · Answer

This one is not bad too    public static String join String delimitor String     subkeys        String result   null      if null  subkeys  amp  amp  subkeys length gt 0            StringBuffer joinBuffer   new StringBuffer subkeys 0            for int idx 1 idx lt subkeys length idx                  joinBuffer append delimitor  append subkeys idx                      result   joinBuffer toString              return result

User · Answer

There has been an open feature request since at least 2009   The long and short of it is that it will part of the functionality of JDK 8 s java util StringJoiner class   http   download java net lambda b81 docs api java util StringJoiner html Here is the Oracle issue if you are interested  http   bugs sun com view bug do bug id 5015163 Here is an example of the new JDK 8 StringJoiner on an array of String String   a   new String    quot first quot   quot second quot   quot third quot    StringJoiner sj   new StringJoiner  quot   quot    for String s a  sj add s   System out println sj     first second third  A utility method in String makes this even simpler  String s   String join  quot   quot   stringArray

User · Answer

Based on all the previous answers   public static String join Iterable lt   extends Object gt  elements  CharSequence separator         StringBuilder builder   new StringBuilder         if  elements    null                Iterator lt   extends Object gt  iter   elements iterator            if iter hasNext                          builder append  String valueOf  iter next                    while iter hasNext                                  builder                      append  separator                        append  String valueOf  iter next                                           return builder toString

User · Answer

There are several examples on DZone Snippets if you want to roll your own that works with a Collection   For example   public static String join AbstractCollection lt String gt  s  String delimiter        if  s    null    s isEmpty    return         Iterator lt String gt  iter   s iterator        StringBuilder builder   new StringBuilder iter next         while  iter hasNext                   builder append delimiter  append iter next               return builder toString

User · Answer

For the sake of completeness  I d like to add that you cannot reverse String split in general  as it accepts a regular expression    hello  world  split        Yields   hello    world     hello world  split        Yields   hello    world      These yield identical results from a different starting point  splitting is not a one-to-one operation  and is thus non-reversible   This all being said  if you assume your parameter to be a fixed string  not regex  then you can certainly do this using one of the many posted answers

[java] A method to reverse effect of java String.split()?

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