this is my first question I've posted. I've used this site to look at other questions to help with similar problems I've had. After some cursory looking I couldn't find quite the answer I was looking for so I decided to finally succumb and create an account.

I am fairly new to java, only a few weeks into my first class. Anyway, my project is to create a program which takes any amount of students and their grades, and then assign them a letter grade. The catch is, however, that it is on a sort of curve and the other grades' letter are dependent on the the highest. Anything equal to or 10 points below the best grade is an a, anything 11-20 points below is a b, and so on. I am to use an array, but I get this error when ran "Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException."

I will go ahead and post my code down below. Thanks for any advice you may be able to give.

package grade.calculator; import java.util.Scanner; /** * * @author nichol57 */ public class GradeCalculator {

/**
 * @param args the command line arguments
 */
public static void main(String[] args) {
   Scanner input = new Scanner(System.in);
   System.out.println("Enter the number of students");
   int number = input.nextInt();
   double[]grades = new double [number];
   for (int J = number; J >=0; J--) {
      System.out.println("Enter the students' grades");
      grades[J] = input.nextDouble();

      }
      double best = grades[0];

     for (int J = 1; J < number; J++) {

      if (grades[J] >= best){
            best = grades[J];
      } 
     }
     for (int J = 0;J < number; J++){    
         if (grades[J] >= best - 10){

            System.out.println("Student " + J + " score is " + grades[J] + 
                    " and grade is " + "A");
         }
         else if (grades[J] >= best - 20){
              System.out.println("Student " + J + " score is " + grades[J] + 
                    " and grade is " + "B");
         }  
         else if (grades[J] >= best - 30) {
              System.out.println("Student " + J + " score is " + grades[J] + 
                    " and grade is " + "C");
         }
         else if (grades[J] >= best - 40) {
              System.out.println("Student " + J + " score is " + grades[J] + 
                    " and grade is " + "D");
         }
         else {
             System.out.println("Student " + J + " score is " + grades[J] + 
                    " and grade is " + "F");
         }
      }  // end for loop for output

   }// end main method

}