Java Array Sort descending?

Question

You could use this to sort all kind of Objects

sort(T[] a, Comparator<? super T> c) 

Arrays.sort(a, Collections.reverseOrder());

Arrays.sort() cannot be used directly to sort primitive arrays in descending order. If you try to call the Arrays.sort() method by passing reverse Comparator defined by Collections.reverseOrder() , it will throw the error

no suitable method found for sort(int[],comparator)

That will work fine with 'Array of Objects' such as Integer array but will not work with a primitive array such as int array.

The only way to sort a primitive array in descending order is, first sort the array in ascending order and then reverse the array in place. This is also true for two-dimensional primitive arrays.

for a list

Collections.sort(list, Collections.reverseOrder());

for an array

Arrays.sort(array, Collections.reverseOrder());

You can use this:

    Arrays.sort(data, Collections.reverseOrder());

Collections.reverseOrder() returns a Comparator using the inverse natural order. You can get an inverted version of your own comparator using Collections.reverseOrder(myComparator).

an alternative could be (for numbers!!!)

1. multiply the Array by -1
2. sort
3. multiply once again with -1

Literally spoken:

array = -Arrays.sort(-array)

without explicit comparator:

Collections.sort(list, Collections.reverseOrder());

with explicit comparator:

Collections.sort(list, Collections.reverseOrder(new Comparator()));

It's not directly possible to reverse sort an array of primitives (i.e., int[] arr = {1, 2, 3};) using Arrays.sort() and Collections.reverseOrder() because those methods require reference types (Integer) instead of primitive types (int).

However, we can use Java 8 Stream to first box the array to sort in reverse order:

// an array of ints
int[] arr = {1, 2, 3, 4, 5, 6};

// an array of reverse sorted ints
int[] arrDesc = Arrays.stream(arr).boxed()
    .sorted(Collections.reverseOrder())
    .mapToInt(Integer::intValue)
    .toArray();

System.out.println(Arrays.toString(arrDesc)); // outputs [6, 5, 4, 3, 2, 1]

Java 8:

Arrays.sort(list, comparator.reversed());

Update: reversed() reverses the specified comparator. Usually, comparators order ascending, so this changes the order to descending.