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Sort descending

I am a new programmer in java, use this site a lot to find out paths. Today I ran into another problem regarding the program I am making for practice.

I have an array:

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

The values ​​for this array are then requested from the user via the 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 create an ascending sort to sort the "score []" values:

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

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

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

I get the error "No suitable sorting method found." Please, help.

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6 answers


There is Arrays

no method in the class sort

that accepts int[]

a Comparator

. Methods sort

in the class Arrays

that accept Comparator

require an array of a reference type (while being int[]

an array of primitive type).

If you change the array type scores

from int[]

to Integer[]

, your code will work as the public static <T> void sort(T[] a, Comparator<? super T> c)

class method Arrays

will match your call Arrays.sort(scores, Collections.reverseOrder());

.



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);
}
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You just need to change the type of the array from Primitive type

to Primitive wrapper class

ie int[] scores = new int [EXAMS]

toInteger[] scores = new Integer[EXAMS]



Arrays.sort

accept a wrapper array in the first argument non-primitive.

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The following actions (using Integer

Objects instead of a 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]
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Arrays.sort(a, Collections.reverseOrder());

does not work with primitives. Try it,

Integer[] a = new Integer[]{1,2,3,5,4};
            Arrays.sort(a,Collections.reverseOrder());
            for(int i:a)
            {
                System.out.println(i);
            }
0


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There is no sorting method for arrays in java. But ArrayList has a sorting method. You can use the following code to sort the list in reverse order.

List l=new ArrayList();
l.add(5);
l.add(1);
l.add(2);
l.add(3);
Collections.sort(l,Collections.reverseOrder());
System.out.println(l);
0


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Collections.reverseOrder()

Will not work because the array is of primitive type. You can go from int to Integer, or try something different like:

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

Your last option is to create your own code.

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