Tic Tac Toe AI [ Minimax Algorithm ] with GUI using JavaFX [Tic Tac Toe][Artificial Intelligence][Minimax][Java][JavaFX]

I made this GUI for the TicTacToe AI: http://coderbots.blogspot.in/2014/08/minimax-algorithm-tic-tac-toe-ai-in.html. The GUI is written in JavaFX. You might wanna give it a shot and see if you can defeat the AI (not possible though).

Lamba Expressions (Java 8): http://coderbots.blogspot.in/2014/08/using-lambdas-java-8-java-8lambda.html

[Make sure you have JDK 8.0 Installed] If not, here's a link: http://www.oracle.com/technetwork/java/javase/downloads/jre8-downloads-2133155.html

Here's a link to a click and run JAR : http://www.mediafire.com/download/yktyrg2w8754yah/TicTacToe_v2.jar
[CSS and Image files included in the JAR. Just open it up with WinRAR, if you feel like seeing the CSS]

Screenshots:

Source [GUI]:

import java.util.Random;
import javafx.application.Application;
import javafx.geometry.Insets;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.image.Image;
import javafx.scene.image.ImageView;
import javafx.scene.layout.GridPane;
import javafx.stage.Stage;

/**
 *
 * @author Jatin Thakur
 */
class Turn {

    enum NextMove {

        O, X, E
    }
    NextMove next;
}

public class TicTacToeAIGUI extends Application {

    Board board = new Board();
    Turn boardTurn = new Turn();
    GridPane grid;
    Label cell1, cell2, cell3,
            cell4, cell5, cell6,
            cell7, cell8, cell9;
    Label[] cells;

    @Override
    public void start(Stage primaryStage) {

        Stage stage = new Stage();
        GridPane g = new GridPane();
        g.setId("firstDialog");
        g.setPadding(new Insets(20, 20, 20, 20));
        g.setVgap(20);
        g.setHgap(20);

        //First Dialog Labels and Buttons
        Label label = new Label("Who will play first?");
        Button IWillPlay = new Button("Lemme play first!");
        Button YouPlay = new Button("You're a legend! you play first!");
        g.add(label, 0, 0, 2, 1);
        g.add(IWillPlay, 0, 1, 1, 1);
        g.add(YouPlay, 1, 1, 1, 1);

        //Scene for the firstDialog
        Scene sc = new Scene(g, 450, 200);
        g.setAlignment(Pos.CENTER);
        sc.getStylesheets().addAll(this.getClass().getResource("firstDialog.css").toExternalForm());
        stage.setTitle("Choose turn");
        stage.setScene(sc);
        stage.setOnCloseRequest(e -> {
            System.exit(0);
        });

        //Board scene
        GridPane grid = new GridPane();
        cell1 = new Label();
        cell2 = new Label();
        cell3 = new Label();
        cell4 = new Label();
        cell5 = new Label();
        cell6 = new Label();
        cell7 = new Label();
        cell8 = new Label();
        cell9 = new Label();

        cells = new Label[]{cell1, cell2, cell3,
            cell4, cell5, cell6,
            cell7, cell8, cell9};

        for (Label cell : cells) {
            cell.setMinSize(128, 128);
            boolean isUsed = false;
            cell.setUserData(isUsed);
        }

        grid.addRow(0, cell1, cell2, cell3);
        grid.addRow(1, cell4, cell5, cell6);
        grid.addRow(2, cell7, cell8, cell9);

        grid.setAlignment(Pos.CENTER);
        grid.setMaxSize(800, 800);
        grid.setGridLinesVisible(true);
        grid.setId("board");

        boardTurn.next = Turn.NextMove.O;
        Image OPic = new Image(getClass().getResourceAsStream("O.png"));
        Image XPic = new Image(getClass().getResourceAsStream("X.png"));

        for (Label cell : cells) {

            cell.setOnMouseClicked(event -> {
                if (((boolean) cell.getUserData()) == false) {
                    cell.setGraphic(new ImageView(XPic));

                    int index = -1;
                    for (int i = 0; i < cells.length; ++i) {
                        if (cell == cells[i]) {
                            index = i;
                        }
                    }

                    board.placeAMove(new Point(index / 3, index % 3), 2);
                    board.displayBoard();
                    System.out.println("Placed a move at: (" + index / 3 + ", " + index % 3 + ")");
                    boolean mark = true;
                    int next = board.returnNextMove();

                    if (next != -1) {   //If the game isn't finished yet!   
                        int indexCell = next;

                        cells[indexCell].setGraphic(new ImageView(OPic));
                        cells[indexCell].setUserData(mark); //Used!
                        System.out.println("Computer has evaluated the next move! " + indexCell);
                        board.placeAMove(new Point(indexCell / 3, indexCell % 3), 1);
                        cell.setUserData(mark);
                    }

                    if (board.isGameOver()) {
                        Stage stage2 = new Stage();
                        GridPane g2 = new GridPane();
                        g2.setPadding(new Insets(20, 20, 20, 20));
                        g2.setVgap(20);
                        g2.setHgap(20);
                        Label label2 = new Label();
                        if (board.hasXWon()) {
                            label2.setText("You better learn to play first, kid!");
                            stage2.setTitle("You lost!");
                        } else {
                            label2.setText("You can't beat me, Stop trying!");
                            stage2.setTitle("It's a draw!");
                        }
                        g2.add(label2, 0, 0, 2, 1);
                        Button onceMore = new Button("Lemme play again!");
                        Button quit = new Button("I'm tired. I quit!");
                        g2.add(onceMore, 1, 1, 1, 1);
                        g2.add(quit, 2, 1, 1, 1);
                        onceMore.setOnMouseClicked(q -> {
                            primaryStage.close();
                            stage2.close();
                            board.resetBoard();
                            start(new Stage());
                        });

                        quit.setOnMouseClicked(q -> {
                            System.exit(0);
                        });
                        Scene scene = new Scene(g2);
                        scene.getStylesheets().addAll(this.getClass().getResource("result.css").toExternalForm());
                        stage2.setScene(scene);
                        stage2.setOnCloseRequest(q -> {
                            primaryStage.close();
                        });
                        stage2.show();
                    }
                }
            });
        };

        Scene scene = new Scene(grid);
        primaryStage.setTitle("Tic Tac Toe");
        primaryStage.setScene(scene);

        scene.getStylesheets().addAll(this.getClass().getResource("board.css").toExternalForm());

        //FirstWindow Action Listeners
        IWillPlay.setOnMouseClicked((event) -> {
            boardTurn.next = Turn.NextMove.X;
            stage.close();
        });

        YouPlay.setOnMouseClicked((event) -> {
            int index = new Random().nextInt(9);
            cells[index].setGraphic(new ImageView(OPic));
            cells[index].setUserData(new Boolean(true));
            board.placeAMove(new Point(index / 3, index % 3), 1);
            boardTurn.next = Turn.NextMove.X;
            stage.close();
        });
        stage.showAndWait();  //Tag1 
        /*
         The placement position of this line (tag1) is important.
         If you place this line above the listeners, the listeners 
         aren't gonna work
         */
        primaryStage.show();
    }

    public static void main(String[] args) {
        launch(args);
    }

}

Source [Logic][Board class]:

import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import java.util.Scanner;

class Point {

    int x, y;

    public Point(int x, int y) {
        this.x = x;
        this.y = y;
    }

    @Override
    public String toString() {
        return "[" + x + ", " + y + "]";
    }
}

class PointAndScore {

    int score;
    Point point;

    PointAndScore(int score, Point point) {
        this.score = score;
        this.point = point;
    }
}

class Board {
 
    List<Point> availablePoints;
    Scanner scan = new Scanner(System.in);
    int[][] board = new int[3][3];

    public Board() {
    }

    public boolean isGameOver() {
        //Game is over is someone has won, or board is full (draw)
        return (hasXWon() || hasOWon() || getAvailableStates().isEmpty());
    }

    public boolean hasXWon() {
        if ((board[0][0] == board[1][1] && board[0][0] == board[2][2] && board[0][0] == 1) || (board[0][2] == board[1][1] && board[0][2] == board[2][0] && board[0][2] == 1)) {
            //System.out.println("X Diagonal Win");
            return true;
        }
        for (int i = 0; i < 3; ++i) {
            if (((board[i][0] == board[i][1] && board[i][0] == board[i][2] && board[i][0] == 1)
                    || (board[0][i] == board[1][i] && board[0][i] == board[2][i] && board[0][i] == 1))) {
                // System.out.println("X Row or Column win");
                return true;
            }
        }
        return false;
    }

    public boolean hasOWon() {
        if ((board[0][0] == board[1][1] && board[0][0] == board[2][2] && board[0][0] == 2) || (board[0][2] == board[1][1] && board[0][2] == board[2][0] && board[0][2] == 2)) {
            // System.out.println("O Diagonal Win");
            return true;
        }
        for (int i = 0; i < 3; ++i) {
            if ((board[i][0] == board[i][1] && board[i][0] == board[i][2] && board[i][0] == 2)
                    || (board[0][i] == board[1][i] && board[0][i] == board[2][i] && board[0][i] == 2)) {
                //  System.out.println("O Row or Column win");
                return true;
            }
        }

        return false;
    }

    public List<Point> getAvailableStates() {
        availablePoints = new ArrayList<>();
        for (int i = 0; i < 3; ++i) {
            for (int j = 0; j < 3; ++j) {
                if (board[i][j] == 0) {
                    availablePoints.add(new Point(i, j));
                }
            }
        }
        return availablePoints;
    }

    public void placeAMove(Point point, int player) {
        board[point.x][point.y] = player;   //player = 1 for X, 2 for O
    } 
    
    void takeHumanInput() {
        System.out.println("Your move: ");
        int x = scan.nextInt();
        int y = scan.nextInt();
        Point point = new Point(x, y);
        placeAMove(point, 2); 
    }

    public void displayBoard() {
        System.out.println();

        for (int i = 0; i < 3; ++i) {
            for (int j = 0; j < 3; ++j) {
                System.out.print(board[i][j] + " ");
            }
            System.out.println();

        }
    } 
    
    Point computersMove; 
    
    public int minimax(int depth, int turn) {  
        if (hasXWon()) return +1; 
        if (hasOWon()) return -1;

        List<Point> pointsAvailable = getAvailableStates();
        if (pointsAvailable.isEmpty()) return 0; 
 
        int min = Integer.MAX_VALUE, max = Integer.MIN_VALUE;
         
        for (int i = 0; i < pointsAvailable.size(); ++i) {  
            Point point = pointsAvailable.get(i);   
            if (turn == 1) { 
                placeAMove(point, 1); 
                int currentScore = minimax(depth + 1, 2);
                max = Math.max(currentScore, max);
                
                if(depth == 0)System.out.println("Score for position "+(i+1)+" = "+currentScore);
                if(currentScore >= 0){ if(depth == 0) computersMove = point;} 
                if(currentScore == 1){board[point.x][point.y] = 0; break;} 
                if(i == pointsAvailable.size()-1 && max < 0){if(depth == 0)computersMove = point;}
            } else if (turn == 2) {
                placeAMove(point, 2); 
                int currentScore = minimax(depth + 1, 1);
                min = Math.min(currentScore, min); 
                if(min == -1){board[point.x][point.y] = 0; break;}
            }
            board[point.x][point.y] = 0; //Reset this point
        } 
        return turn == 1?max:min;
    }  
    
    //Functions for GUI
    public int returnNextMove() {
        if (isGameOver()) return -1;
        minimax(0, 1); 
        return computersMove.x * 3 + computersMove.y;
    }

    public void resetBoard(){
        for(int i = 0;i<3;++i)
            for(int j=0;j<3;++j)
                board[i][j] = 0;
    }
}

Minimax Algorithm Tic Tac Toe AI In Java [Minimax][Full tree Search][Artificial Intelligence][Java]

The minimax tree has leaf values like -1 0 or 1. Min selects the minimum i.e. -1. Max selects the maximum among the available after Min would have taken its move. i.e. 0 or 1. So it has available moves like -1, -1, 0, 0, +1, +1 at the top most node (root, which is the present game state) and selects the first +1 value as it has a chance of victory no matter what other opponent does (it has already been calculated like if the opponent does this, I can do this (it always assumes the opponent takes the smartest move to destroy you) and I can win). There is no summation of values taking place like +3, +4, +1 so that max selects +3 and like that. This kind of approach is used in other implementation where you don't have the time to evaluate the whole tree and just want to evaluate the tree at the (say 4th) level and then rank the states accordingly like I have 3 rows in which I can get 3 Xs so that gives a score +1000, 2 rows = +100 and 1 row = +10. -ve values for the opponents position. So you get values like +1200 or -2300 at the leaves from where you select the move which is favorable (this player is not perfect, it can lose. It has not evaluated all the possibilites. It has just gone to some extent of computation to get some available move in some limited time).

This AI is a perfect player i.e. it can never lose. It wins or it draws the match.

Source: The code isn't really hard. Function names are self explanatory. Comments are added wherever necessary. I've supposed that 2 is the human player playing the game and 1 is the computer. If you want to see the actual calculations, just uncomment the commented lines.

[Make sure you have JDK 8.0 Installed] If not, here's a link: http://www.oracle.com/technetwork/java/javase/downloads/jre8-downloads-2133155.html

import java.util.*;

class Point {

    int x, y;

    public Point(int x, int y) {
        this.x = x;
        this.y = y;
    }

    @Override
    public String toString() {
        return "[" + x + ", " + y + "]";
    }
}

class PointsAndScores {

    int score;
    Point point;

    PointsAndScores(int score, Point point) {
        this.score = score;
        this.point = point;
    }
}

class Board {
 
    List<Point> availablePoints;
    Scanner scan = new Scanner(System.in);
    int[][] board = new int[3][3];

    public Board() {
    }

    public boolean isGameOver() {
        //Game is over is someone has won, or board is full (draw)
        return (hasXWon() || hasOWon() || getAvailableStates().isEmpty());
    }

    public boolean hasXWon() {
        if ((board[0][0] == board[1][1] && board[0][0] == board[2][2] && board[0][0] == 1) || (board[0][2] == board[1][1] && board[0][2] == board[2][0] && board[0][2] == 1)) {
            //System.out.println("X Diagonal Win");
            return true;
        }
        for (int i = 0; i < 3; ++i) {
            if (((board[i][0] == board[i][1] && board[i][0] == board[i][2] && board[i][0] == 1)
                    || (board[0][i] == board[1][i] && board[0][i] == board[2][i] && board[0][i] == 1))) {
                // System.out.println("X Row or Column win");
                return true;
            }
        }
        return false;
    }

    public boolean hasOWon() {
        if ((board[0][0] == board[1][1] && board[0][0] == board[2][2] && board[0][0] == 2) || (board[0][2] == board[1][1] && board[0][2] == board[2][0] && board[0][2] == 2)) {
            // System.out.println("O Diagonal Win");
            return true;
        }
        for (int i = 0; i < 3; ++i) {
            if ((board[i][0] == board[i][1] && board[i][0] == board[i][2] && board[i][0] == 2)
                    || (board[0][i] == board[1][i] && board[0][i] == board[2][i] && board[0][i] == 2)) {
                //  System.out.println("O Row or Column win");
                return true;
            }
        }

        return false;
    }

    public List<Point> getAvailableStates() {
        availablePoints = new ArrayList<>();
        for (int i = 0; i < 3; ++i) {
            for (int j = 0; j < 3; ++j) {
                if (board[i][j] == 0) {
                    availablePoints.add(new Point(i, j));
                }
            }
        }
        return availablePoints;
    }

    public void placeAMove(Point point, int player) {
        board[point.x][point.y] = player;   //player = 1 for X, 2 for O
    }

    public Point returnBestMove() {
        int MAX = -100000;
        int best = -1;

        for (int i = 0; i < rootsChildrenScores.size(); ++i) { 
            if (MAX < rootsChildrenScores.get(i).score) {
                MAX = rootsChildrenScores.get(i).score;
                best = i;
            }
        }

        return rootsChildrenScores.get(best).point;
    }

    void takeHumanInput() {
        System.out.println("Your move: ");
        int x = scan.nextInt();
        int y = scan.nextInt();
        Point point = new Point(x, y);
        placeAMove(point, 2); 
    }

    public void displayBoard() {
        System.out.println();

        for (int i = 0; i < 3; ++i) {
            for (int j = 0; j < 3; ++j) {
                System.out.print(board[i][j] + " ");
            }
            System.out.println();

        }
    }

    public int returnMin(List<Integer> list) {
        int min = Integer.MAX_VALUE;
        int index = -1;
        for (int i = 0; i < list.size(); ++i) {
            if (list.get(i) < min) {
                min = list.get(i);
                index = i;
            }
        }
        return list.get(index);
    }

    public int returnMax(List<Integer> list) {
        int max = Integer.MIN_VALUE;
        int index = -1;
        for (int i = 0; i < list.size(); ++i) {
            if (list.get(i) > max) {
                max = list.get(i);
                index = i;
            }
        }
        return list.get(index);
    }

    List<PointsAndScores> rootsChildrenScores;
 
    public void callMinimax(int depth, int turn){
        rootsChildrenScores = new ArrayList<>();
        minimax(depth, turn);
    }
    
    public int minimax(int depth, int turn) {

        if (hasXWon()) return +1;
        if (hasOWon()) return -1;

        List<Point> pointsAvailable = getAvailableStates();
        if (pointsAvailable.isEmpty()) return 0; 

        List<Integer> scores = new ArrayList<>(); 

        for (int i = 0; i < pointsAvailable.size(); ++i) {
            Point point = pointsAvailable.get(i);  

            if (turn == 1) { //X's turn select the highest from below minimax() call
                placeAMove(point, 1); 
                int currentScore = minimax(depth + 1, 2);
                scores.add(currentScore);

                if (depth == 0) 
                    rootsChildrenScores.add(new PointsAndScores(currentScore, point));
                
            } else if (turn == 2) {//O's turn select the lowest from below minimax() call
                placeAMove(point, 2); 
                scores.add(minimax(depth + 1, 1));
            }
            board[point.x][point.y] = 0; //Reset this point
        }
        return turn == 1 ? returnMax(scores) : returnMin(scores);
    }
}

public class TicTacToe {

    public static void main(String[] args) {
        Board b = new Board();
        Random rand = new Random();
        
        b.displayBoard();

        System.out.println("Who's gonna move first? (1)Computer (2)User: ");
        int choice = b.scan.nextInt();
        if(choice == 1){
            Point p = new Point(rand.nextInt(3), rand.nextInt(3));
            b.placeAMove(p, 1);
            b.displayBoard();
        }
        
        while (!b.isGameOver()) {
            System.out.println("Your move: ");
            Point userMove = new Point(b.scan.nextInt(), b.scan.nextInt());

            b.placeAMove(userMove, 2); //2 for O and O is the user
            b.displayBoard();
            if (b.isGameOver()) {
                break;
            } 
            b.callMinimax(0, 1);
            for (PointsAndScores pas : b.rootsChildrenScores) {
                System.out.println("Point: " + pas.point + " Score: " + pas.score);
            }
            b.placeAMove(b.returnBestMove(), 1);
            b.displayBoard();
        }
        if (b.hasXWon()) {
            System.out.println("Unfortunately, you lost!");
        } else if (b.hasOWon()) {
            System.out.println("You win! This is not going to get printed.");
        } else {
            System.out.println("It's a draw!");
        }
    }
}

Sample run:

0 0 0
0 0 0
0 0 0
Who's gonna move first? (1)Computer (2)User:
2
Your move:
2 2

0 0 0
0 0 0
0 0 2
Point: [0, 0] Score: -1
Point: [0, 1] Score: -1
Point: [0, 2] Score: -1
Point: [1, 0] Score: -1
Point: [1, 1] Score: 0
Point: [1, 2] Score: -1
Point: [2, 0] Score: -1
Point: [2, 1] Score: -1

0 0 0
0 1 0
0 0 2
Your move:
0 0

2 0 0
0 1 0
0 0 2
Point: [0, 1] Score: 0
Point: [0, 2] Score: -1
Point: [1, 0] Score: 0
Point: [1, 2] Score: 0
Point: [2, 0] Score: -1
Point: [2, 1] Score: 0

2 1 0
0 1 0
0 0 2
Your move:
2 1

2 1 0
0 1 0
0 2 2
Point: [0, 2] Score: -1
Point: [1, 0] Score: -1
Point: [1, 2] Score: -1
Point: [2, 0] Score: 0

2 1 0
0 1 0
1 2 2
Your move:
0 2

2 1 2
0 1 0
1 2 2
Point: [1, 0] Score: -1
Point: [1, 2] Score: 0

2 1 2
0 1 1
1 2 2
Your move:
1 0

2 1 2
2 1 1
1 2 2
It's a draw!

Update:
Here is an improved version. We don't need to evaluate more when we already have found a winning move, so we just skip rest of the evaluations as soon as we get +1 (for max) or -1 (for min) for some state for the next move.

Source:

import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import java.util.Scanner;

class Point {

    int x, y;

    public Point(int x, int y) {
        this.x = x;
        this.y = y;
    }

    @Override
    public String toString() {
        return "[" + x + ", " + y + "]";
    }
}

class PointAndScore {

    int score;
    Point point;

    PointAndScore(int score, Point point) {
        this.score = score;
        this.point = point;
    }
}

class Board {
 
    List<Point> availablePoints;
    Scanner scan = new Scanner(System.in);
    int[][] board = new int[3][3];

    public Board() {
    }

    public boolean isGameOver() {
        //Game is over is someone has won, or board is full (draw)
        return (hasXWon() || hasOWon() || getAvailableStates().isEmpty());
    }

    public boolean hasXWon() {
        if ((board[0][0] == board[1][1] && board[0][0] == board[2][2] && board[0][0] == 1) || (board[0][2] == board[1][1] && board[0][2] == board[2][0] && board[0][2] == 1)) {
            //System.out.println("X Diagonal Win");
            return true;
        }
        for (int i = 0; i < 3; ++i) {
            if (((board[i][0] == board[i][1] && board[i][0] == board[i][2] && board[i][0] == 1)
                    || (board[0][i] == board[1][i] && board[0][i] == board[2][i] && board[0][i] == 1))) {
                // System.out.println("X Row or Column win");
                return true;
            }
        }
        return false;
    }

    public boolean hasOWon() {
        if ((board[0][0] == board[1][1] && board[0][0] == board[2][2] && board[0][0] == 2) || (board[0][2] == board[1][1] && board[0][2] == board[2][0] && board[0][2] == 2)) {
            // System.out.println("O Diagonal Win");
            return true;
        }
        for (int i = 0; i < 3; ++i) {
            if ((board[i][0] == board[i][1] && board[i][0] == board[i][2] && board[i][0] == 2)
                    || (board[0][i] == board[1][i] && board[0][i] == board[2][i] && board[0][i] == 2)) {
                //  System.out.println("O Row or Column win");
                return true;
            }
        }

        return false;
    }

    public List<Point> getAvailableStates() {
        availablePoints = new ArrayList<>();
        for (int i = 0; i < 3; ++i) {
            for (int j = 0; j < 3; ++j) {
                if (board[i][j] == 0) {
                    availablePoints.add(new Point(i, j));
                }
            }
        }
        return availablePoints;
    }

    public void placeAMove(Point point, int player) {
        board[point.x][point.y] = player;   //player = 1 for X, 2 for O
    } 
    
    void takeHumanInput() {
        System.out.println("Your move: ");
        int x = scan.nextInt();
        int y = scan.nextInt();
        Point point = new Point(x, y);
        placeAMove(point, 2); 
    }

    public void displayBoard() {
        System.out.println();

        for (int i = 0; i < 3; ++i) {
            for (int j = 0; j < 3; ++j) {
                System.out.print(board[i][j] + " ");
            }
            System.out.println();

        }
    } 
    
    Point computersMove; 
    
    public int minimax(int depth, int turn) {  
        if (hasXWon()) return +1; 
        if (hasOWon()) return -1;

        List<Point> pointsAvailable = getAvailableStates();
        if (pointsAvailable.isEmpty()) return 0; 
 
        int min = Integer.MAX_VALUE, max = Integer.MIN_VALUE;
         
        for (int i = 0; i < pointsAvailable.size(); ++i) {  
            Point point = pointsAvailable.get(i);   
            if (turn == 1) { 
                placeAMove(point, 1); 
                int currentScore = minimax(depth + 1, 2);
                max = Math.max(currentScore, max);
                
                if(depth == 0)System.out.println("Score for position "+(i+1)+" = "+currentScore);
                if(currentScore >= 0){ if(depth == 0) computersMove = point;} 
                if(currentScore == 1){board[point.x][point.y] = 0; break;} 
                if(i == pointsAvailable.size()-1 && max < 0){if(depth == 0)computersMove = point;}
            } else if (turn == 2) {
                placeAMove(point, 2); 
                int currentScore = minimax(depth + 1, 1);
                min = Math.min(currentScore, min); 
                if(min == -1){board[point.x][point.y] = 0; break;}
            }
            board[point.x][point.y] = 0; //Reset this point
        } 
        return turn == 1?max:min;
    }  
}

public class TicTacToe {

    public static void main(String[] args) {
        Board b = new Board();
        Random rand = new Random();
        
        b.displayBoard();

        System.out.println("Select turn:\n\n1. Computer 2. User: ");
        int choice = b.scan.nextInt();
        if(choice == 1){
            Point p = new Point(rand.nextInt(3), rand.nextInt(3));
            b.placeAMove(p, 1);
            b.displayBoard();
        }
        
        while (!b.isGameOver()) {
            System.out.println("Your move: ");
            Point userMove = new Point(b.scan.nextInt(), b.scan.nextInt());

            b.placeAMove(userMove, 2); //2 for O and O is the user
            b.displayBoard();
            if (b.isGameOver()) break;
            
            b.minimax(0, 1);  
            
            b.placeAMove(b.computersMove, 1);
            b.displayBoard();
        }
        if (b.hasXWon()) 
            System.out.println("Unfortunately, you lost!");
        else if (b.hasOWon()) 
            System.out.println("You win!"); //Can't happen
        else 
            System.out.println("It's a draw!");
    }
}

Output:

0 0 0
0 0 0
0 0 0
Select turn:

1. Computer 2. User:
2
Your move:
2 2

0 0 0
0 0 0
0 0 2
Score for position 1 = -1
Score for position 2 = -1
Score for position 3 = -1
Score for position 4 = -1
Score for position 5 = 0
Score for position 6 = -1
Score for position 7 = -1
Score for position 8 = -1

0 0 0
0 1 0
0 0 2
Your move:
0 0

2 0 0
0 1 0
0 0 2
Score for position 1 = 0
Score for position 2 = -1
Score for position 3 = 0
Score for position 4 = 0
Score for position 5 = -1
Score for position 6 = 0

2 0 0
0 1 0
0 1 2
Your move:
0 1

2 2 0
0 1 0
0 1 2
Score for position 1 = 0
Score for position 2 = -1
Score for position 3 = -1
Score for position 4 = -1

2 2 1
0 1 0
0 1 2
Your move:
2 0

2 2 1
0 1 0
2 1 2
Score for position 1 = 0
Score for position 2 = -1

2 2 1
1 1 0
2 1 2
Your move:
1 2

2 2 1
1 1 2
2 1 2
It's a draw!

More: 

Tic-Tac-Toe (JavaFX UI)
Minimax With Alpha-Beta Pruning (Tic-Tac-Toe)

Connect 4 AI (Minimax)
Conncet 4 AI (Minimax + Alpha-Beta Pruning)