Largest product in a grid

public class main {
    public static void main(String [] args){
        int Grid [][] = {
        {8,02,22,97,38,15,00,40,00,75,04,05,07,78,52,12,50,77,91,8},
        {49,49,99,40,17,81,18,57,60,87,17,40,98,43,69,48,04,56,62,00},
        {81,49,31,73,55,79,14,29,93,71,40,67,53,88,30,03,49,13,36,65},
        {52,70,95,23,04,60,11,42,69,24,68,56,01,32,56,71,37,02,36,91},
        {22,31,16,71,51,67,63,89,41,92,36,54,22,40,40,28,66,33,13,80},
        {24,47,32,60,99,03,45,02,44,75,33,53,78,36,84,20,35,17,12,50},
        {32,98,81,28,64,23,67,10,26,38,40,67,59,54,70,66,18,38,64,70},
        {67,26,20,68,02,62,12,20,95,63,94,39,63,8,40,91,66,49,94,21},
        {24,55,58,05,66,73,99,26,97,17,78,78,96,83,14,88,34,89,63,72},
        {21,36,23,9,75,00,76,44,20,45,35,14,00,61,33,97,34,31,33,95},
        {78,17,53,28,22,75,31,67,15,94,03,80,04,62,16,14,9,53,56,92},
        {16,39,05,42,96,35,31,47,55,58,88,24,00,17,54,24,36,29,85,57},
        {86,56,00,48,35,71,89,07,05,44,44,37,44,60,21,58,51,54,17,58},
        {19,80,81,68,05,94,47,69,28,73,92,13,86,52,17,77,04,89,55,40},
        {04,52,8,83,97,35,99,16,07,97,57,32,16,26,26,79,33,27,98,66},
        {88,36,68,87,57,62,20,72,03,46,33,67,46,55,12,32,63,93,53,69},
        {04,42,16,73,38,25,39,11,24,94,72,18,8,46,29,32,40,62,76,36},
        {20,69,36,41,72,30,23,88,34,62,99,69,82,67,59,85,74,04,36,16},
        {20,73,35,29,78,31,90,01,74,31,49,71,48,86,81,16,23,57,05,54},
        {01,70,54,71,83,51,54,69,16,92,33,48,61,43,52,01,89,19,67,48}
        };

        int Product = 0;
        int largest = 0;

        // Check horizontally
        for(int i = 0; i < 20; i++){
            for(int j = 0; j < 17; j++){
                Product = Grid[i][j] * Grid[i][j + 1] * Grid[i][j + 2] * Grid[i][j + 3];
                if(Product > largest){
                    largest = Product;
                }
            }   
        }

        // Check vertically
        for(int i = 0; i < 17; i ++){
            for(int j = 0; j < 20; j++){
                Product = Grid[i][j] * Grid[i + 1][j] * Grid[i + 2][j] * Grid[i + 3][j];
                if(Product > largest){
                    largest = Product;
                }
            }
        }

        // Check diagonally right
        for(int i = 0; i < 17; i++){
            for(int j = 0; j < 17; j++){
                Product = Grid[i][j] * Grid[i + 1][j + 1] * Grid[i + 2][j + 2] * Grid[i + 3][i + 3];
                if(Product > largest){
                    largest = Product;
                }
            }
        }

        // Check diagonally left
        for(int i = 0; i < 17; i ++){
            for(int j = 3; j < 20; j ++){
                Product = Grid[i][j] * Grid[i + 1][j - 1] * Grid[i + 2][j  - 2] * Grid[i + 3][j - 3];
                if(Product > largest){
                    largest = Product;
                }
            }
        }
        System.out.format("Max Product = %d", + largest);
    }
}