public class Test {
    public static void main(String[] args) {
        int[][] grid;

        // A B C D E F G
        // 0 1 2 3 4 5 6

        String map = "ABCDEFG";

        while true {
            String userInput = "A5";

            char letter = userInput.charAt(0);   // 'A'
            char number = userInput.charAt(1);   // '5'

            int rowIndex = convertLetterToRow(letter);
            int[] row = grid[rowIndex];

            int columnIndex = convertNumberToColumn(number);
            int item = row[columnIndex];
        }
    }

    public static int convertLetterToRow(char letter) {
        if (letter == 'A') {
            return 0;
        } else if (letter == 'B') {
            return 1;
        } ...
    }
}