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

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

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, !

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);

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

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();
}

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();
}

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, !"

Google guava's library also has [this kind of capability][1]. 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| [1]: http://guava-libraries.googlecode.com/svn/trunk/javadoc/com/google/common/base/Joiner.html

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 " & ".

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

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

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");

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();
}

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.

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)));
}

Nothing built-in that I know of.

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

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();
}

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();
}

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, "");
}

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());
}

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

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.

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(" "));

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)

> 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);

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]);
}