Collecting value of int array using normal JAVA Stream

You can solve your issue like so :

String output = Arrays.stream(arr)
        .boxed()
        .map(String::valueOf)
        .collect(Collectors.joining(",")); // 0,1,8,10,12,56,78

Explain what happen :

when you use Arrays.asList() which look :

public static <T> List<T> asList(T... a) {
    return new ArrayList<>(a);
}

it took varargs of type T, in your case you use it for int[] Object, so Arrays.asList() will return List of int[] and not a stream of ints, so instead you have to use Arrays.stream which look like this :

public static IntStream stream(int[] array) {
    return stream(array, 0, array.length);
}

to get the correct data.

Arrays.asList(arr) returns a List<int[]> whose only element is arr. Therefore streaming that List and then mapping that single element to String.valueOf(x) and collecting with Collectors.joining(",") will result in a String whose value is that single array's toString(), which is the output you see.

String output = Arrays.asList(arr) // List<int[]>
    .stream() // Stream<int[]>
    .map(x -> String.valueOf(x)) // Stream<String> having a single element - "[I@776ec8df"
    .collect(Collectors.joining(",")); // "[I@776ec8df"

When you create an IntStream from the int array, you get a stream of the individual elements (the int values), so you can box them, convert then to Strings and join them to get the desired output.

You can make your first snippet work if you change:

int arr[] = new int[] {10,1,56,8,78,0,12};

to:

Integer arr[] = new Integer[] {10,1,56,8,78,0,12};

since this way Arrays.asList(arr) will produce a List<Integer> containing all the elements of the input array.