Java: Documenting this method Please help me explain this code line by line by h

Question

Java: Documenting this method

Please help me explain this code line by line by helping me document this method above the "// TODO: document this method" in the code below for countingSort and radixSort. I already implemented the method, but just need help documenting the method for countingSort and radixSort line by line.

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public class PA2 {

   // TODO: document this method
   public static int[] countingSort(int[] a) {
//TODO: implement this method
if (a.length == 0) {
return a;
}

int max = a[0];

for (int i = 1; i < a.length; i++)
if (a[i] > max)
max = a[i];

int[] count = new int[max > a.length ? max + 1 : a.length + 1];
int[] sorted = new int[a.length];

for (int element = 0; element < a.length; element++)
count[a[element]]++;

for (int i = 0, j = 0; i < count.length; i++)
{
while (count[i] != 0)
{
sorted[j] = i;
count[i]--;
j++;

}
}

return sorted;
}

   // TODO: document this method
   public static int[] radixSort(int[] a) {
   // TODO: implement this method
       if (a.length == 0) {
return a;
}

       int max = a[0];
int num = 1;

int[] arr2 = new int[1000]; // Array2 size of 1000

for (int i = 1; i < a.length; i++)
{
if (a[i] > max)
{
max = a[i];
}
}

// System.out.println("hello");
// int d = String.valueOf(max).length();

while (max / num > 0) {

int[] arr = new int[10];

for (int i = 0; i < a.length; i++)
arr[((a[i] / num) % 10)]++;

for (int i = 1; i < arr.length; i++)
arr[i] += arr[i - 1];

for (int i = a.length - 1; i >= 0; i--)
arr2[--arr[(a[i] / num) % 10]] = a[i];

for (int i = 0; i < a.length; i++)
a[i] = arr2[i];

num *= 10;
}

return a;
}

Explanation / Answer

public class PA2 {
   // TODO: document this method
   public static int[] countingSort(int[] a) {
       // If the array is empty, just return
       if (a.length == 0) {
           return a;
       }
      
       // assume first element to be the max, we will later modify it accordingly
       int max = a[0];
      
       // find the maximum element in array
       for (int i = 1; i < a.length; i++)
           if (a[i] > max)
               max = a[i];
      
       // Create array to store the counts
       // This should be sufficient to hold elements equal to max element
       int[] count = new int[max > a.length ? max + 1 : a.length + 1];
      
       // to store the result in sorted order
       int[] sorted = new int[a.length];
      
       // Count how many times a elmenet has appeared in array
       for (int element = 0; element < a.length; element++)
           count[a[element]]++;
      
       // Now populate the sorted aray based on count
       // So if count array is 0,2,1,2 for lets say 4 elements from 0 to 3
       // then result would be 1,1,2,3,3
       for (int i = 0, j = 0; i < count.length; i++) {
           while (count[i] != 0) {
               sorted[j] = i;
               count[i]--;
               j++;
           }
       }
      
       // return result
       return sorted;
   }

   // TODO: document this method
   public static int[] radixSort(int[] a) {
       // If the array is empty, just return
       if (a.length == 0) {
           return a;
       }

       // assume first element to be the max, we will later modify it accordingly
       int max = a[0];
      
       // find the maximum element in array
       for (int i = 1; i < a.length; i++) {
           if (a[i] > max) {
               max = a[i];
           }
       }
      
       int num = 1;
       int[] arr2 = new int[1000]; // Array2 size of 1000
      
       // In each iteration, num will be multiplied by 10
       // and we try to sort the current digit
       while (max / num > 0) {
           // temporary array
           int[] arr = new int[10];
          
           // Store the count for the positions of current digit in temp array
           for (int i = 0; i < a.length; i++)
               arr[((a[i] / num) % 10)]++;
          
           // Change arr[i] so that arr[i] now contains actual
       // position of this digit in output
           for (int i = 1; i < arr.length; i++)
               arr[i] += arr[i - 1];
          
           // build output array using the count above
           for (int i = a.length - 1; i >= 0; i--)
               arr2[--arr[(a[i] / num) % 10]] = a[i];
          
           // Copy to output array, so that it now
       // contains sorted numbers according to current digit
           for (int i = 0; i < a.length; i++)
               a[i] = arr2[i];
          
           // increase the base to shift towards right digit
           num *= 10;
       }
       return a;
   }
}

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