TicTacToe 2.0

package tictactoe;

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

public class TicTacToe {

    private final String PLAYER_CHARACTER = "X";
    private final String COMPUTER_CHARACTER = "O";
    private final String[] grid = new String[9];

    public TicTacToe() {
        gameLoop();
    }

    private void gameLoop() {
        Scanner input = new Scanner(System.in);
        gridInitialization();

        while (hasWinner()) {
            humanPlayer(input);
            if (isDraw()) return;
            computerPlayer();
            displayGrid();
        }
    }

    private void gridInitialization() {
        for (int i = 0; i < grid.length; i++) {
            grid[i] = String.valueOf(i + 1);
        }
    }

    private void humanPlayer(Scanner input) {
        int player;
        System.out.println("Pick a number from 1 - 9 ");
        player = input.nextInt();
        while (isTileTaken(grid[index(player)])) {
            System.out.println("Try again that tile is taken");
            player = input.nextInt();
        }
        grid[index(player)] = PLAYER_CHARACTER;
    }

    private void computerPlayer() {
        int computer;
        computer = (int) (Math.random() * 9 + 1);
        while (isTileTaken(grid[index(computer)])) {
            computer = (int) (Math.random() * 9 + 1);
        }
        grid[index(computer)] = COMPUTER_CHARACTER;
    }

    private boolean isDraw() {
        if (Arrays.stream(grid).distinct().count() == 2 && hasWinner()) {
            System.out.println("DRAW");
            return true;
        }
        return false;
    }

    private boolean isTileTaken(String tile) {
        return tile.equals("X") || tile.equals("O");
    }

    private void displayGrid() {
        /*
            WHAT is the question
         */
        int LAST_ROW_INDEX = 3;
        for (int i = 1; i < grid.length + 1; i++) {
            if(i % LAST_ROW_INDEX == 0) {
                System.out.print(grid[index(i)] + "\n");
            }else {
                System.out.print(grid[index(i)] + "|");
            }
        }
    }

    private int index(int i) {
        return i - 1;
    }

    private boolean hasWinner() {
        if (isWinner(PLAYER_CHARACTER)) {
            System.out.println("Player Won\nGame Over");
            return false;
        } else if (isWinner(COMPUTER_CHARACTER)) {
            System.out.println("Computer Won\nGame Over");
            return false;
        }
        return true;
    }

    private boolean isWinner(String userCharacter) {
        return hasWonHorizontally(userCharacter)
                || hasWonVertically(userCharacter)
                || hasWonDiagonally(userCharacter);
    }

    private boolean hasWonDiagonally(String userCharacter) {
        return grid[0].equals(userCharacter) && grid[4].equals(userCharacter) && grid[8].equals(userCharacter)
                || grid[2].equals(userCharacter) && grid[4].equals(userCharacter) && grid[6].equals(userCharacter);
    }

    private boolean hasWonVertically(String userCharacter) {
        return grid[0].equals(userCharacter) && grid[3].equals(userCharacter) && grid[6].equals(userCharacter)
                || grid[1].equals(userCharacter) && grid[4].equals(userCharacter) && grid[7].equals(userCharacter)
                || grid[2].equals(userCharacter) && grid[5].equals(userCharacter) && grid[8].equals(userCharacter);
    }

    private boolean hasWonHorizontally(String userCharacter) {
        return grid[0].equals(userCharacter) && grid[1].equals(userCharacter) && grid[2].equals(userCharacter)
                || grid[3].equals(userCharacter) && grid[4].equals(userCharacter) && grid[5].equals(userCharacter)
                || grid[6].equals(userCharacter) && grid[7].equals(userCharacter) && grid[8].equals(userCharacter);
    }
}