A Quick and How to Join Array Elements With a Separator (The Opposite of Split) in Java

A quick and easy way to join array elements with a separator (the opposite of split) in Java

Using Java 8 you can do this in a very clean way:

String.join(delimiter, elements);

This works in three ways:

1) directly specifying the elements

String joined1 = String.join(",", "a", "b", "c");

2) using arrays

String[] array = new String[] { "a", "b", "c" };
String joined2 = String.join(",", array);

3) using iterables

List<String> list = Arrays.asList(array);
String joined3 = String.join(",", list);

Java: join array of primitives with separator

Here what I came up with. There are several way to do this and they are depends on the tools you using.

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Using StringUtils and ArrayUtils from Common Lang:

int[] arr = new int[] {1, 2, 3, 4, 5, 6, 7};
String result = StringUtils.join(ArrayUtils.toObject(arr), " - ");

You can't just use StringUtils.join(arr, " - "); because StringUtils doesn't have that overloaded version of method. Though, it has method StringUtils.join(int[], char).

Works at any Java version, from 1.2.

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Using Java 8 streams:

Something like this:

int[] arr = new int[] {1, 2, 3, 4, 5, 6, 7};
String result = Arrays.stream(arr)
        .mapToObj(String::valueOf)
        .collect(Collectors.joining(" - "));

In fact, there are lot of variations to achive the result using streams.

Java 8's method String.join() works only with strings, so to use it you still have to convert int[] to String[].

String[] sarr = Arrays.stream(arr).mapToObj(String::valueOf).toArray(String[]::new);
String result = String.join(" - ", sarr);

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If you stuck using Java 7 or earlier with no libraries, you could write your own utility method:

public static String myJoin(int[] arr, String separator) {
    if (null == arr || 0 == arr.length) return "";

    StringBuilder sb = new StringBuilder(256);
    sb.append(arr[0]);

    //if (arr.length == 1) return sb.toString();

    for (int i = 1; i < arr.length; i++) sb.append(separator).append(arr[i]);

    return sb.toString();
}

Than you can do:

int[] arr = new int[] {1, 2, 3, 4, 5, 6, 7};
String result = myJoin(arr, " - ");

Opposite of String.Split with separators (.net)

Found the answer. It's called String.Join.

A quick and easy way to join array elements with a separator (the opposite of split) in Java

Using Java 8 you can do this in a very clean way:

String.join(delimiter, elements);

This works in three ways:

1) directly specifying the elements

String joined1 = String.join(",", "a", "b", "c");

2) using arrays

String[] array = new String[] { "a", "b", "c" };
String joined2 = String.join(",", array);

3) using iterables

List<String> list = Arrays.asList(array);
String joined3 = String.join(",", list);

Alternative for String.join in Android?

You can use TextUtils.join instead:

String result = TextUtils.join(", ", list);

(String.join was added in Java 8, which is why you can't use it in Android.)

Convert string array to strings with a whitespace separating them

You can use this code to get String with whitespace.

String[] array = {"a", "b", "c"};
String output = "";
for (int i = 0; i < array.length; i++) {
    output += array[i] + " ";
}

My reverse a string code includes a space at the end of the string

Avoid space at end by adding a if statement which skips last iteration

public class Reverse {
    public static void main(String[] args){
        for(int i = args.length - 1; i >= 0; i--){
            for(int j = args[i].length() - 1; j >= 0; j--){
                System.out.print(args[i].charAt(j));
            }
            if(i != 0){
                System.out.print(" ");
            }
        }
    }
}

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