Tic Tac Toe Game - Minimax Algorithm

I have been trying to create an algorithm for the computer in my Tic-Tac-Toe game? So I searched for some good ones, and found about this confusing but effective algorithm, at least if you get it working, called Minimax. I tried implementing it into my game. Let's say it was easier said than done. Sometimes I think it's working, but sometimes it doesn't work at all. How do I get my algorithm working? What the variables BEST_SCORE_COMPUTER and BEST_SCORE_PLAYER in my code should have as starting values.

Java Code:

import java.util.Scanner;
public class TicTacToe{
private static char BOARD[] = {' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ', ' '}; // This is the main board itself.
private static int ROWS[][] = {{0, 1, 2}, {3, 4, 5}, {6, 7, 8}, {0, 3, 6}, {1, 4, 7}, {2, 5, 8}, {0, 4, 8}, {2, 4, 6}}; // These are all the rows one can win by filling.
private static int SCORE, BEST_MOVE_COMPUTER, BEST_SCORE_COMPUTER = -1, BEST_SCORE_PLAYER = 1; // These variables speak for themselves.
private static byte TURN = 1; // 1 means player's turn, and 2 means computer's turn.

[Code] .....