Suppose, I have an array:
int[] arr = new int[] {1, 2, 3, 4, 5, 6, 7}; And I need to join its elements using separator, for example, " - ", so as the result I should get string like this:
"1 - 2 - 3 - 4 - 5 - 6 - 7" How could I do this?
PS: yes, I know about this and this posts, but its solutions won't work with an array of primitives.
Here's what I came up with. There are several ways to do this and they depend on the tools you are using.
Using StringUtils and ArrayUtils from Commons 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.
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 achieve it 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); If you're 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(); } Then you can do:
int[] arr = new int[] {1, 2, 3, 4, 5, 6, 7}; String result = myJoin(arr, " - "); 
.collect(Collectors.joining(",")) instead of the temp string array.
Arrays.stream(arr) produces an IntStream and in it there is no such collect() method.Java 8 Solution would be like this:
Stream.of(1,2,3,4).map(String::valueOf).collect(Collectors.joining("-")) In Java 8+ you could use an IntStream and a StringJoiner. Something like,
int[] arr = new int[] { 1, 2, 3, 4, 5, 6, 7 }; StringJoiner sj = new StringJoiner(" - "); IntStream.of(arr).forEach(x -> sj.add(String.valueOf(x))); System.out.println(sj.toString()); Output is (as requested)
1 - 2 - 3 - 4 - 5 - 6 - 7 You can use Guava for joining elements. More examples and docs you can find there. https://github.com/google/guava/wiki/StringsExplained
Joiner.on("-") .join(texts); To be more precise you should firstly wrap your array into a List with Arrays.asList() or Guava's primitive-friendly equivalents.
Joiner.on("-") .join(Arrays.asList(1, 2, 3, 4, 5, 6, 7)); Joiner.on("-") .join(Ints.asList(arr)); 
.asList() methods, e.g. Ints.asList() - you can't use Array.asList() with primitive arrays.Arrays.asList(arr) will produce a List with size of 1 =) And that's one element will be our primitive array.int[] arr = new int[] { 1, 2, 3, 4, 5, 6, 7 }; IntStream.of(arr).mapToObj(i -> String.valueOf(i)).collect(Collectors.joining(",")) ; 
I'm sure there's a way to do this in Kotlin/Scala or other JVM languages as well but you could always stick to keeping things simple for a small set of values like you have above:
int i, arrLen = arr.length; StringBuilder tmp = new StringBuilder(); for (i=0; i<arrLen-1; i++) tmp.append(arr[i] +" - "); tmp.append(arr[arrLen-1]); System.out.println( tmp.toString() ); If your delimiter is a single char you can use StringUtils from Common Lang:
int[] arr = {1, 2, 3, 4, 5, 6, 7}; String result = StringUtils.join(arr, '-'); However, if the delimiter is a String, you should use an alternative because StringUtils is behaving badly (see this ticket).
I've been looking for a way to join primitives in a Stream without first instantiating strings for each one of them. I've come to this but it still requires boxing them.
LongStream.range(0, 500).boxed().collect(Collector.of(StringBuilder::new, (sb, v) -> { if (sb.length() != 0) sb.append(','); sb.append(v.longValue()); }, (a, b) -> a.length() == 0 ? b : b.length() != 0 ? a.append(',').append(b) : a, StringBuilder::toString)); For Java 7 or earlier.
public static StringBuilder join(CharSequence delimiter, int... arr) { if (null == delimiter || null == arr) throw new NullPointerException(); StringBuilder sb = new StringBuilder(String.valueOf(arr[0])); for (int i = 1; i < arr.length; i++) sb.append(delimiter).append(arr[i]); return sb; } public static void main(String[] args) { StringBuilder sb = join(" - ", 1, 2, 3, 4); System.out.println(sb.toString());//you could pass sb also coz println automatically call toString method within it System.out.println(sb.insert(0, "[").append("]")); } Output:
1 - 2 - 3 - 4
[1 - 2 - 3 - 4]
