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

http://docs.oracle.com/javase/1.5.0/docs/api/java/util/Arrays.html#toString(int[]) — Ofiris, Feb 19 '13 at 12:57

score 56 · Accepted Answer · edited Dec 30 '15 at 12:30

56

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 < 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).

edited Dec 30 '15 at 12:30

Jared Rummler

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answered Feb 19 '13 at 12:54

Naveen Kumar Alone

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Answer that provides only a code snippet is not very helpful. Please consider adding some comments or briefly explain what it does. :) – bahrep Feb 19 '13 at 13:15
1

It's still the best answer as others use string concatenation – Steve Kuo Jun 21 '13 at 18:27
11

Use StringBuilder instead of StringBuffer. StringBuffer is thread-safe and not needed in this example. – walv Jun 18 '14 at 15:02
1

+1 for being the fastest solution I 've tried so far! – vefthym Jul 14 '14 at 12:00
@walv thanks walv for your great suggestion and i have modified my answer :) – Naveen Kumar Alone May 28 '15 at 06:32

Achintya Jha · Answer 2 · 2013-02-19T13:01:31.300

16

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:

edited Feb 19 '13 at 13:01

answered Feb 19 '13 at 12:52

Achintya Jha

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Please don't concatenate strings, use StringBuilder/Buffer or whatever appropriate. – Radek Skokan Nov 15 '13 at 12:00
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I cant believe that 13 ppl actually agreed with String concatenation?! I want to double Radek - use StringBuilder instead – Deian May 27 '15 at 13:54

score 16 · Answer 3 · answered Feb 19 '13 at 12:56

16

Simple answer:

Arrays.toString(arr);

answered Feb 19 '13 at 12:56

Marco

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Arrays.toString(arr) gives the result like [1,2,3].He is not required this format – Arun Kumar Mudraboyina May 17 '13 at 11:41

Bernhard Barker · Answer 4 · 2013-02-19T13:04:38.627

6

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"};

edited Feb 19 '13 at 13:04

answered Feb 19 '13 at 12:56

Bernhard Barker

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if you are concatenating really BIG strings, then you shouldn't ask i == iMax? in each iteration! Just ALWAYS add a separator and then delete the last one after the loop! – Sauer May 06 '13 at 15:33
@Sauer Note that I didn't write that first code sample myself, it's a direct copy-and-paste from the Java API. Do you mean a really big **array**? The size of the strings won't matter for the `i == iMax` check. Also note that checking `i == iMax` is a *really*, **really** fast operation (and you need a check to determine the end of the for-loop in either way, so it may as well be there; note the for-loop does **not** look like this: `for (int i = 0; i != iMax; i++)`). – Bernhard Barker May 06 '13 at 15:41

cw' · Answer 5 · 2015-08-17T12:46:51.973

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").

VHS · Answer 6 · 2017-10-26T19:04:29.980

4

Do it java 8 way in just 1 line:

String.join("", arr);

edited Oct 26 '17 at 19:04

answered Sep 20 '17 at 19:29

VHS

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score 3 · Answer 7 · answered Jun 11 '14 at 01:48

3

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"

answered Jun 11 '14 at 01:48

Tho

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score 3 · Answer 8 · edited Jul 23 '14 at 17:18

3

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());
 }

edited Jul 23 '14 at 17:18

spassas

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answered Jul 23 '14 at 17:05

user96279

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Since you don't need the concurrency, a `StringBuilder` is typically suggested over a `StringBuffer`. Additionally, the body of the loop should probably be `strb.append(String.valueOf(id)).append(delimiter);` so as to completely avoid the `+` on the `String`. – Patrick Aug 12 '14 at 17:15

score 2 · Answer 9 · answered Feb 19 '13 at 12:56

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.

walv · Answer 10 · 2014-06-18T15:00:18.250

2

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)

edited Jun 18 '14 at 15:00

answered Jun 18 '14 at 12:55

walv

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score 2 · Answer 11 · answered Dec 04 '14 at 17:15

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

DarckBlezzer · Answer 12 · 2016-09-20T15:30:52.740

2

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 ""

edited Sep 20 '16 at 15:30

answered Sep 15 '16 at 21:58

DarckBlezzer

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score 1 · Answer 13 · edited May 23 '17 at 10:31

1

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.

edited May 23 '17 at 10:31

Community

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answered Feb 19 '13 at 12:57

Ben

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it is important to note that `Arrays.toString(arr)` does not print the array by itself...it only provides the String to be printed – Logan Murphy Dec 04 '14 at 19:10

score 0 · Answer 14 · edited May 23 '17 at 12:17

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

score 0 · Answer 15 · 2014-12-04T16:57:49.620

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> val a = Array("1", "2", "3")
a: Array[String] = Array(1, 2, 3)

scala> val aString = a.mkString
aString: String = 123

scala> println(aString)
123

score 0 · Answer 16 · answered Jul 30 '17 at 08:06

0

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

answered Jul 30 '17 at 08:06

Fahmi Eshaq

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Sushanth Bangera · Answer 17 · 2018-01-31T10:34:23.200

0

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);

edited Jan 31 '18 at 10:34

answered Aug 23 '17 at 19:49

Sushanth Bangera

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LittleBigUllah · Answer 18 · 2017-10-26T17:08:35.127

0

Example using Java 8.

  String[] arr = {"1", "2", "3"};
  String join = String.join("", arr);

I hope that helps

edited Oct 26 '17 at 17:08

answered Oct 25 '17 at 21:55

LittleBigUllah

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You need to change `are` to `arr`. – MarredCheese Oct 25 '17 at 22:25

score -1 · Answer 19 · edited Oct 25 '17 at 02:47

-1

String newString= Arrays.toString(oldString).replace("[","").replace("]","").replace(",","").trim();

edited Oct 25 '17 at 02:47

Stephen Rauch

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answered Oct 25 '17 at 02:28

Abhijeet Rawat

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Concatenating elements in an array to a string

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