Lagrange Polynomial Java code

The Lagrange interpolating polynomial is simply a reformulation of the Newton polynomial
that avoids the computation of divided differences. It can be represented concisely as

where

where Π designates the “product of.” For example, the linear version (n = 1) is 

and the second-order version is

Consequently, the summation of all the products designated by first equation is the unique nthorder

polynomial that passes exactly through all n + 1 data points.

Reference; Numerical Methods for Engineers. Steven C. Chapra and Raymond P. Canale

public static void main (String[] args)
 {
  //Lagrange Polynomial
  double[] x= new double[] {1,4,6};
  double[] y= new double[] {0,1.386294,1.791760};
  int n,grade;
  double xval,sum, product;
  xval=2;
  sum=0;
  grade=2;
  n=grade+1;
  
  for (int i=0; i<n; i++){
   product=y[i];
   
   for (int j=0; j<n; j++){
    if(i!=j){
     product=product*(xval-x[j])/(x[i]-x[j]);
    }
    
   }
   sum=sum+product;
  }
  System.out.println(sum);
 }