Java: Reverse sorting array method

Your algorithm is correct. But you are swapping unnecessarily even if the you have a small number. I updated you logic.

import java.io.*;
public class Hey{
    public static void main(String args[])throws IOException{
        int []ar = {1,2,5,4,6,8,7,9,10};
        selectionReverseSort(ar);
    }
    public static void selectionReverseSort (int[] array){
        int startScan, index, maxIndex, maxValue;
        for (startScan = 0; startScan < (array.length - 1); startScan++){
            maxIndex = startScan;
            maxValue = array[startScan];

            for(index = startScan + 1; index < array.length; index++){
                //index is 1
                if (array[index] > maxValue){
                    maxValue = array[index];
                    //maxValue now becomes the second array number
                    maxIndex = index;
                    //maxIndex becomes the current index number.
                    //swap only if the condition is true
                    array[maxIndex] = array[startScan];
                    array[startScan] = maxValue;
                }
            }
        }
    }
    for(int i = 0; i < array.length; i++ )
        System.out.println(array[i]+"");
   }
}

And I suggest you to use any other better sorting algorithm than Insertion sort.

It appears that the algorithm you've chosen is to find the largest value in the array, then use a swap to move the largest value to the first position in the array. Then you do the same for the subarray starting with the second element, then with the subarray starting with the third, and so on.

This will work, but your code does the swap too early. You need to wait until your inner loop is done finding the largest element before you do the swap. I haven't tested it, but I think all you need to do is move these two statements:

array[maxIndex] = array[startScan];
array[startScan] = maxValue;

outside of the inner loop.

This is just a one-line solution by using java API:

public static void selectionReverseSort (int[] array){
    Collections.sort(Arrays.asList(array),Collections.reverseOrder());
}

Keep it for future purpose :).