CODEWITHSUNDEEP
javaarrays
Nick Heiner
Nick Heiner

Reputation: 122530

Java function for arrays like PHP's join()?

I want to join a String[] with a glue string. Is there a function for this?

Upvotes: 270

Views: 129833

Answers (24)

Martin Zeitler
Martin Zeitler

Reputation: 76769

As already mentioned, class StringJoiner is also an available option since Java 8:

@NotNull
String stringArrayToCsv(@NotNull String[] data) {
    if (data.length == 0) {return "";}
    StringJoiner joiner = new StringJoiner(", ");
    Iterator<String> itr = Arrays.stream(data).iterator();
    while (itr.hasNext()) {joiner.add(itr.next());}
    return joiner.toString();
}

However, the traditional String.join() is less imports and less code:

@NotNull
String stringArrayToCsv(@NotNull String[] data) {
    if (data.length == 0) {return "";}
    return String.join(", ", data);
}

Upvotes: 0

Mr.Q
Mr.Q

Reputation: 4524

Whatever approach you choose, be aware of null values in the array. Their string representation is "null" so if it is not your desired behavior, skip null elements.

String[] parts = {"Hello", "World", null, "!"};
Stream.of(parts)
      .filter(Objects::nonNull)
      .collect(Collectors.joining(" "));

Upvotes: 0

coobird
coobird

Reputation: 160992

Starting from Java8 it is possible to use String.join().

String.join(", ", new String[]{"Hello", "World", "!"})

Generates:

Hello, World, !

Otherwise, Apache Commons Lang has a StringUtils class which has a join function which will join arrays together to make a String.

For example:

StringUtils.join(new String[] {"Hello", "World", "!"}, ", ")

Generates the following String:

Hello, World, !

Upvotes: 318

everlasto
everlasto

Reputation: 4930

A little mod instead of using substring():

//join(String array,delimiter)
public static String join(String r[],String d)
{
        if (r.length == 0) return "";
        StringBuilder sb = new StringBuilder();
        int i;
        for(i=0;i<r.length-1;i++){
            sb.append(r[i]);
            sb.append(d);
        }
        sb.append(r[i]);
        return sb.toString();
}

Upvotes: 27

Dmitry Zaytsev
Dmitry Zaytsev

Reputation: 23972

In case you're using Functional Java library and for some reason can't use Streams from Java 8 (which might be the case when using Android + Retrolambda plugin), here is a functional solution for you:

String joinWithSeparator(List<String> items, String separator) {
    return items
            .bind(id -> list(separator, id))
            .drop(1)
            .foldLeft(
                    (result, item) -> result + item,
                    ""
            );
}

Note that it's not the most efficient approach, but it does work good for small lists.

Upvotes: 0

ema
ema

Reputation: 951

To get "str1, str2" from "str1", "str2", "" :

Stream.of("str1", "str2", "").filter(str -> !str.isEmpty()).collect(Collectors.joining(", "));

Also you can add extra null-check

Upvotes: 0

Jay
Jay

Reputation: 27492

You could easily write such a function in about ten lines of code:

String combine(String[] s, String glue)
{
  int k = s.length;
  if ( k == 0 )
  {
    return null;
  }
  StringBuilder out = new StringBuilder();
  out.append( s[0] );
  for ( int x=1; x < k; ++x )
  {
    out.append(glue).append(s[x]);
  }
  return out.toString();
}

Upvotes: 53

icza
icza

Reputation: 418137

As with many questions lately, Java 8 to the rescue:

Java 8 added a new static method to java.lang.String which does exactly what you want:

public static String join(CharSequence delimeter, CharSequence... elements);

Using it:

String s = String.join(", ", new String[] {"Hello", "World", "!"});

Results in:

"Hello, World, !"

Upvotes: 18

Jackson Ray Hamilton
Jackson Ray Hamilton

Reputation: 9466

My spin.

public static String join(Object[] objects, String delimiter) {
  if (objects.length == 0) {
    return "";
  }
  int capacityGuess = (objects.length * objects[0].toString().length())
      + ((objects.length - 1) * delimiter.length());
  StringBuilder ret = new StringBuilder(capacityGuess);
  ret.append(objects[0]);
  for (int i = 1; i < objects.length; i++) {
    ret.append(delimiter);
    ret.append(objects[i]);
  }
  return ret.toString();
}

public static String join(Object... objects) {
  return join(objects, "");
}

Upvotes: 2

Marek Gregor
Marek Gregor

Reputation: 3851

In Java 8 you can use

1) Stream API :

String[] a = new String[] {"a", "b", "c"};
String result = Arrays.stream(a).collect(Collectors.joining(", "));

2) new String.join method: https://stackoverflow.com/a/21756398/466677

3) java.util.StringJoiner class: http://docs.oracle.com/javase/8/docs/api/java/util/StringJoiner.html

Upvotes: 59

Ryoichiro Oka
Ryoichiro Oka

Reputation: 1997

Do you like my 3-lines way using only String class's methods?

static String join(String glue, String[] array) {
    String line = "";
    for (String s : array) line += s + glue;
    return (array.length == 0) ? line : line.substring(0, line.length() - glue.length());
}

Upvotes: 1

sp00m
sp00m

Reputation: 48837

Just for the "I've the shortest one" challenge, here are mines ;)

Iterative:

public static String join(String s, Object... a) {
    StringBuilder o = new StringBuilder();
    for (Iterator<Object> i = Arrays.asList(a).iterator(); i.hasNext();)
        o.append(i.next()).append(i.hasNext() ? s : "");
    return o.toString();
}

Recursive:

public static String join(String s, Object... a) {
    return a.length == 0 ? "" : a[0] + (a.length == 1 ? "" : s + join(s, Arrays.copyOfRange(a, 1, a.length)));
}

Upvotes: 5

Gaurav Adurkar
Gaurav Adurkar

Reputation: 864

There is simple shorthand technique I use most of the times..

String op = new String;
for (int i : is) 
{
    op += candidatesArr[i-1]+",";
}
op = op.substring(0, op.length()-1);

Upvotes: -2

spanky762
spanky762

Reputation: 171

I do it this way using a StringBuilder:

public static String join(String[] source, String delimiter) {
    if ((null == source) || (source.length < 1)) {
        return "";
    }

    StringBuilder stringbuilder = new StringBuilder();
    for (String s : source) {
        stringbuilder.append(s + delimiter);
    }
    return stringbuilder.toString();
} // join((String[], String)

Upvotes: -1

Noah
Noah

Reputation: 15330

If you were looking for what to use in android, it is:

String android.text.TextUtils.join(CharSequence delimiter, Object[] tokens)

for example:

String joined = TextUtils.join(";", MyStringArray);

Upvotes: 73

William Simpson
William Simpson

Reputation: 21

A similar alternative

/**
 * @param delimiter 
 * @param inStr
 * @return String
 */
public static String join(String delimiter, String... inStr)
{
    StringBuilder sb = new StringBuilder();
    if (inStr.length > 0)
    {
        sb.append(inStr[0]);
        for (int i = 1; i < inStr.length; i++)
        {
            sb.append(delimiter);                   
            sb.append(inStr[i]);
        }
    }
    return sb.toString();
}

Upvotes: 2

quietmint
quietmint

Reputation: 14153

If you've landed here looking for a quick array-to-string conversion, try Arrays.toString().

Creates a String representation of the Object[] passed. The result is surrounded by brackets ("[]"), each element is converted to a String via the String.valueOf(Object) and separated by ", ". If the array is null, then "null" is returned.

Upvotes: 6

devstopfix
devstopfix

Reputation: 6808

If you are using the Spring Framework then you have the StringUtils class:

import static org.springframework.util.StringUtils.arrayToDelimitedString;

arrayToDelimitedString(new String[] {"A", "B", "C"}, "\n");

Upvotes: 9

Bertie
Bertie

Reputation: 17697

Google guava's library also has this kind of capability. You can see the String[] example also from the API.

As already described in the api, beware of the immutability of the builder methods.

It can accept an array of objects so it'll work in your case. In my previous experience, i tried joining a Stack which is an iterable and it works fine.

Sample from me :

Deque<String> nameStack = new ArrayDeque<>();
nameStack.push("a coder");
nameStack.push("i am");
System.out.println("|" + Joiner.on(' ').skipNulls().join(nameStack) + "|");

prints out : |i am a coder|

Upvotes: 14

Rob S.
Rob S.

Reputation: 2548

Given:

String[] a = new String[] { "Hello", "World", "!" };

Then as an alternative to coobird's answer, where the glue is ", ":

Arrays.asList(a).toString().replaceAll("^\\[|\\]$", "")

Or to concatenate with a different string, such as " &amp; ".

Arrays.asList(a).toString().replaceAll(", ", " &amp; ").replaceAll("^\\[|\\]$", "")

However... this one ONLY works if you know that the values in the array or list DO NOT contain the character string ", ".

Upvotes: 9

Richard Corfield
Richard Corfield

Reputation: 717

This is how I do it.

private String join(String[] input, String delimiter)
{
    StringBuilder sb = new StringBuilder();
    for(String value : input)
    {
        sb.append(value);
        sb.append(delimiter);
    }
    int length = sb.length();
    if(length > 0)
    {
        // Remove the extra delimiter
        sb.setLength(length - delimiter.length());
    }
    return sb.toString();
}

Upvotes: 4

JonMR
JonMR

Reputation: 586

Nothing built-in that I know of.

Apache Commons Lang has a class called StringUtils which contains many join functions.

Upvotes: 4

Adriaan Koster
Adriaan Koster

Reputation: 16209

java.util.Arrays has an 'asList' method. Together with the java.util.List/ArrayList API this gives you all you need:;

private static String[] join(String[] array1, String[] array2) {

    List<String> list = new ArrayList<String>(Arrays.asList(array1));
    list.addAll(Arrays.asList(array2));
    return list.toArray(new String[0]);
}

Upvotes: -3

Brad Beattie
Brad Beattie

Reputation:

Not in core, no. A search for "java array join string glue" will give you some code snippets on how to achieve this though.

e.g.

public static String join(Collection s, String delimiter) {
    StringBuffer buffer = new StringBuffer();
    Iterator iter = s.iterator();
    while (iter.hasNext()) {
        buffer.append(iter.next());
        if (iter.hasNext()) {
            buffer.append(delimiter);
        }
    }
    return buffer.toString();
}

Upvotes: 8

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