Concatenating elements in an array to a string

Question

I m confused a bit  I couldn t find the answer anywhere     I ve got an String array   String   arr     1    2    3      then I convert it to a string by   String str   Arrays toString arr   System out println str     I expected to get the string  123   but I got the string   1 2 3   instead   How could I do it in java  I m using Eclipse IDE

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I have just written the following   public static String toDelimitedString int   ids  String delimiter        StringBuffer strb   new StringBuffer        for  int id   ids              strb append String valueOf id    delimiter             return strb substring 0  strb length   - delimiter length

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Arrays toString is formatting the output  added the brackets and commas   you should implement your own method of toString   public String toString String   arr       String result           for String s   arr          result  s      return result       edit  Stringbuilder is better though  see above

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Here is a way to do it       Arrays toString array  substring 1  3 array length-1   replaceAll            Here is a demo class   package arraytostring demo   import java util Arrays   public class Array2String            public static void main String   args                     String   array      1    2    3    4    5    6    7                     System out println array2String array                       output is  1234567                    public static String array2String String   array                     return Arrays toString array  substring 1   3   array length - 1                                    replaceAll                            Scala makes this easier  cleaner and safer   scala gt  val a   Array  1    2    3   a  Array String    Array 1  2  3   scala gt  val aString   a mkString aString  String   123  scala gt  println aString  123

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take a look at generic method to print all elements in an array  but in short  the Arrays toString arr  is just a easy way of printing the content of a primative array

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Arrays toString   from the API  at least for the Object   version of it   public static String toString Object   a        if  a    null          return  null       int iMax   a length - 1      if  iMax    -1          return            StringBuilder b   new StringBuilder        b append           for  int i   0    i              b append String valueOf a i             if  i    iMax              return b append      toString            b append                  So that means it inserts the   at the start  the   at the end  and the   between elements   If you want it without those characters   StringBuilder is faster than the below  but it can t be the small amount of code   String str       for  String i arr    str    i  System out println str     Side note   String    arr 3    1 2 3  won t compile   Presumably you wanted  String   arr     1    2    3

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Arrays toString   can be used to convert String Array to String  The extra characters can be removed by using Regex expressions or simply by using replace method   Arrays toString strArray  replace          replace          replace             Java 8 has introduced new method for String join  public static String join CharSequence delimiter  CharSequence    elements   String join     strArray

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Do it java 8 way in just 1 line   String join     arr

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Simple answer   Arrays toString arr

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Use the Arrays toString   function  It keeps your code short and readable  It uses a string builder internally  thus  it s also efficient  To get rid of the extra characters  you might chose to eliminate them using the String replace   function  which  admittedly  reduces readability again   String str   Arrays toString arr  replaceAll                      This is similar to the answer of Tris Nefzger  but without the lengthy substring construction to get rid of the square brackets    Explanation of the Regex      means any of      and     and       The      tells the Java String that we are not meaning some special character  like a new line   n  or a tab   t   but a real backslash       So instead of        the Regex interpreter reads       which tells it that we mean a literal square bracket and do not want to use it as part of the Regex language  for instance     3    denotes any number of characters  but none of them should be  3

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Use StringBuilder instead of StringBuffer  because it is faster than StringBuffer    Sample code  String   strArr     1    2    3    StringBuilder strBuilder   new StringBuilder    for  int i   0  i  lt  strArr length  i         strBuilder append strArr i      String newString   strBuilder toString      Here s why this is a better solution to using string concatenation  When you concatenate 2 strings  a new string object is created and character by character copy is performed  Effectively meaning that the code complexity would be the order of the squared of the size of your array     1 2 3      n which is the number of characters copied per iteration   StringBuilder would do the  copying to a string  only once in this case reducing the complexity to O n

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For Spring based projects   org springframework util StringUtils arrayToDelimitedString Object   arr  String delim   For Apache Commons users  set of nice join methods   org apache commons lang StringUtils join Object   array  char separator

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Example using Java 8     String   arr     1    2    3      String join   String join     arr     I hope that helps

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String newString  Arrays toString oldString  replace         replace         replace         trim

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Arrays toString arr     output is  1 2 3  and you storing it to your string   and printing it so you get output  1 2 3    If you want to get output 123 try this   public static void main String   args        String   arr    1   2   3        String output          for String str  arr          output output str      System out println output         Output   123

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This is a little code of convert string array to string without    or    or    String   strArray   new String    Java    String    Array    To    String    Example     String str   Arrays toString strArray               str   str substring 1  str length  -1  replaceAll              First convert array to string  Second get text from x to y position  third replace all     with

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Object class has toString method  All other classes extending it overrides the toString method so in for arrays also toString is overrided in this way  So if you want your output in your way you need to create your own method by which you will get your desired result   str     for  Integer i arr        str  i toString        Hope this helps  refer Why does the toString method in java not seem to work for an array

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Guava has Joiner utility to resolve this issue   Example   String joinWithoutSeparator   Joiner on     join 1  2  3      returns  123  String joinWithSeparator   Joiner on      join 1  2  3      returns  1 2 3

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For those who develop in Android  use TextUtils   String items   TextUtils join     arr     Assuming arr is of type String   arr    1   2   3     The output would be 123

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Using Guava s Joiner  which in r18 internally uses StringBuilder   String    arr    1   2   3    Joiner noSpaceJoiner   Joiner on      noSpaceJoiner join arr     Joiner is useful because it is thread-safe and immutable and can be reused in many places without having to duplicate code  In my opinion it also is more readable     Using Java 8 s Stream support  we can also reduce this down to a one-liner   String concat   Stream of arr  collect Collectors joining       Both outputs in this case are 123

[java] Concatenating elements in an array to a string

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