TicTacToe.java

  int[][] data = new int[3][3];
  
	private void aiMove() {
		Score s = minimax(null, true);
		data[s.move.x][s.move.y] = COMPUTER;
	}
	
	static class Score {
		Point move;
		int score;

		public Score(Point move, int score) {
			this.move = move;
			this.score = score;
		}
	};

	private Score minimax(Point move, final boolean maximizing) {
		if (gameEnd()) {
			return new Score(null, score()); // use score only
		}

		Score best = new Score(null, maximizing ? -10 : 10);

		for (int i = 0; i < 3; i++) {
			for (int j = 0; j < 3; j++) {
				if (data[i][j] == 0) {
				  // for each empty cells
					Point child = new Point(i, j);

					data[i][j] = maximizing ? COMPUTER : YOU;
					Score score = minimax(child, !maximizing); 
					// find mini or max
					if (maximizing && score.score > best.score) {
						best.score = score.score;
						best.move = child;
					} else if (!maximizing && score.score < best.score) {
						best.score = score.score;
						best.move = child;
					}
					data[i][j] = 0; // backtracking
				}
			}
		}
		return best;
	}

	private int score() {
		int winner = winner();
		if (winner == COMPUTER)
			return 1;
		if (winner == YOU)
			return -1;
		return 0;
	}