Array Sorting Descending Order

Question

I'm a new programmer to java, been using this website a lot to learn the ways. Today I've stumbled into another problem towards a program I'm doing for practice.

I have an array:

    final int EXAMS = 5;
    int[] scores = new int [EXAMS];

The values for this array are then asked from the user through a Scanner object:

for (int index = 0; index < EXAMS; index++)
    {
        System.out.println("Enter the score for " + (index+1) +":");
        scores[index] = kb.nextInt();
        if (scores[index] < 0){
            System.out.println("The number you have entered is invalid.");
            scores[index] = kb.nextInt();
        }
    }

I managed to make an ascending order sorting of the values "scores[]":

       Arrays.sort(scores);
        System.out.println("The sorted int array is:");
        for (int number : scores) 
        {
            System.out.println("Number = "+ number);
        }

But I want the sorting to be in descending order. When I put the

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

I get an error saying: "no suitable method found for sorting." Please help.

Solution 1

There's no sort method in Arrays class that accepts an int[] and a Comparator. The sort methods in the Arrays class that accept a Comparator require an array of reference type (while an int[] is an array of a primitive type).

If you change the type of your scores array from int[] to Integer[], your code will work, since the method public static <T> void sort(T[] a, Comparator<? super T> c) of the Arrays class will match your Arrays.sort(scores, Collections.reverseOrder()); call.

final int EXAMS = 5;
Integer[] scores = new Integer [EXAMS]; // the only required change
for (int index = 0; index < EXAMS; index++) {
    System.out.println("Enter the score for " + (index+1) +":");
    scores[index] = kb.nextInt();
    if (scores[index] < 0){
        System.out.println("The number you have entered is invalid.");
        scores[index] = kb.nextInt();
    }
}
Arrays.sort(scores, Collections.reverseOrder());
System.out.println("The sorted int array is:");
for (int number : scores)  {
    System.out.println("Number = "+ number);
}

Solution 2

The following works (using the Integer Objects instead of primitive int):

Integer[] test = {1, 2, 4, 3, 5};
Arrays.sort(test, Collections.reverseOrder());
System.out.println(Arrays.toString(test)); // [5, 4, 3, 2, 1]

Solution 3

Collections.reverseOrder() 

Won't work because the array is of primitive type. You can change from int to Integer or try something different like:

Arrays.sort(scores);
ArrayUtils.reverse(scores);

Your final option would be to make your own code.

Solution 4

You just need to change your array type from Primitive type to Primitive wrapper class i.e. int[] scores = new int [EXAMS] to Integer[] scores = new Integer[EXAMS]

Arrays.sort accept wrapper array in the first argument not primitive.

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