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The required JAVA program is given below,

import java.util.Arrays;
import java.util.Scanner;

class Ideone {
   // Finding the index of largest element
   public static int indexOfLargestElement(double[] array){
       double maxValue = array[0];
       int maxIndex = 0;
       // finding maximum value
   for (int i = 0; i < array.length; i++) {
           if (maxValue < array[i]) {
               maxValue = array[i];
           }
       }
       // finding first index of max value
       for (int i = 0; i < array.length; i++) {
           if (maxValue == array[i]) {
               maxIndex=i;
           }
       }
       return maxIndex;
   }
  
   public static void main(String args[]) {
   Scanner s = new Scanner(System.in);
       // input length of array , it can be hardcoded as 10
   System.out.println("Enter the length of the input array:");
   int length = s.nextInt();
   double [] array = new double[length];
       // entering the elements
   System.out.println("Enter the elements:");
   for(int i=0; i<length; i++ ) {
   array[i] = s.nextDouble();
   }
       // printing output
       System.out.println("Index of largest element is :");
   System.out.println(indexOfLargestElement(array));
}
}