Java Array Sort Descending

java

sorting

comparator

arrays

byAlex Kataev·Oct 11, 2024

Efficiently sort a Java array in descending order by combining Arrays.sort() and Collections.reverseOrder() for object types including Integer:

Integer[] array = {3, 1, 4, 5, 2};
Arrays.sort(array, Collections.reverseOrder()); // Result: [5, 4, 3, 2, 1]

For primitive types such as int, you can leverage streams:

int[] array = {3, 1, 4, 5, 2};
int[] descSorted = Arrays.stream(array)
    .boxed()
    .sorted(Collections.reverseOrder())
    .mapToInt(Integer::intValue)
    .toArray(); // Voila! [5, 4, 3, 2, 1]

Sorting with custom comparators

Custom conditions for sorting can be effortlessly achieved using a Comparator. Collections.reverseOrder(myComparator) does the trick:

Comparator<CustomObject> myComparator = Comparator.comparing(CustomObject::getAttributeName).reversed();
Arrays.sort(customObjectArray, myComparator); // Congrats! Your array is sorted in descending order

Sorting lists in a descending way

Lists can be sorted too, using the Collections.sort() method in combination with Collections.reverseOrder():

List<Integer> list = Arrays.asList(3, 1, 4, 5, 2);
Collections.sort(list, Collections.reverseOrder()); // Result: [5, 4, 3, 2, 1]

This method bypasses the need for manual sorting, saving your effort.

Descending with two-dimensional primitive arrays

Two-dimensional primitive arrays need each row to be sorted in ascending order first, followed by reversing each row:

int[][] multiArray = {{3, 5}, {1, 4}};
for (int[] row : multiArray) {
    Arrays.sort(row);
    reverseArrayInPlace(row); // Reverse sort, because why not? 
}

Traps and pitfalls to sidestep

Here are a few key things to remember:

Box primitive arrays when using Collections.reverseOrder().
In-place array reversal alleviates additional space complexity: so reverse like a pro!
When implementing reverseArrayInPlace, maintain efficiency to avoid causing bottlenecks.

Advanced sorting scenarios

In complex scenarios, for instance, sorting objects per multiple criteria, make use of Comparator.comparing() chained with .thenComparing():

Arrays.sort(objectsArray, Comparator.comparing(ObjectType::getPrimaryAttribute)
    .thenComparing(ObjectType::getSecondaryAttribute)
    .reversed());

With this, you're sorting your array primarily by one attribute and secondarily by another, all in descending order.

explain-codes / Java / Java Array Sort Descending

Linked

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"comparison method violates its general contract!"