Hello

please help me to fix my code, try it in ur devices to see the result:

Java Code: 
package Tictactoe;

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
/**
 *
 * @author ituser
 */
import java.util.*;

public class Tictactoe1 {

    private static final int ROWS = 3;
    private static final int COLUMNS = 3;
    private static String[][] board;
    //construct an empty board

    public Tictactoe1() {
        board = new String[ROWS][COLUMNS];
        //Fill with spaces
        for (int i = 0; i < ROWS; i++) {
            for (int j = 0; j < COLUMNS; j++) {
                board[i][j] = " ";
            }
        }
    }

//set the fields in the board
    public String set(int i, int j, String player) {
        if (board[i][j].equals(" ")) {
            board[i][j] = player;
        } else {
            return " ";
        }
        return board[i][j];
    }
//set the fields in the board

    public boolean checkDiagL(String player) {
        boolean found = false;
        int count = 0;
        int i = 0;
        int j = 0;
        while (i < ROWS) {
            if (board[i][j].equals(player)) {
                count++;
                i++;
                j++;
            } else {
                break;
            }
        }
        if (count == ROWS) {
            found = true;
        }
        return found;
    }

    public boolean checkDiagR(String player) {
        boolean found = false;
        int count = 0;
        int i = 0;
        int j = COLUMNS - 1;
        while (i < ROWS) {
            if (board[i][j].equals(player)) {
                count++;
                i++;
                j--;
            } else {
                break;
            }
        }
        if (count == ROWS) {
            found = true;
        }
        return found;
    }

    public boolean checkHorizontal(String player) {
        boolean found = false;
        int count = 0;
        for (int i = 0; i < ROWS; i++) {
            for (int j = 0; j < COLUMNS; j++) {
                if (board[i][j].equals(player)) {
                    count++;
                } else {
                    break;
                }
            }
            if (count == ROWS) {
                found = true;
                break;
            } else {
                count = 0;
            }
        }
        return found;
    }

    public boolean checkVertical(String player) {
        boolean found = false;
        int count = 0;
        for (int j = 0; j < COLUMNS; j++) {
            for (int i = 0; i < ROWS; i++) {
                if (board[i][j].equals(player)) {
                    count++;
                } else {
                    break;
                }
            }
            if (count == COLUMNS) {
                found = true;
                break;
            } else {
                count = 0;
            }
        }
        return found;
    }

    public static String preventdiagonalsLeft() {
        String player = "x";
        boolean found = false;
        int i = 0;
        int j = 0;
        int count = 0;
        String block = "";
        while (i < ROWS) {
            if (board[i][j] == player) {
                count++;
            } else if (board[i][j] == " ") {
                block = "Block: " + i + " " + j;
            }
            i++;
            j++;
        }
        if (count == 2) {
            found = true;
            return block;
        }

        return "";
    }

    public static String preventdiagonalsRight() {
        String player = "x";
        boolean found = false;
        int i = 0;
        int j = 2;
        int count = 0;
        String block = "";
        while (i < ROWS) {
            if (board[i][j] == player) {
                count++;
            } else if (board[i][j] == " ") {
                block = "Block: " + i + " " + j;
            }
            i++;
            j--;
        }
        if (count == 2) {
            found = true;
            return block;
        }

        return "";
    }

    public static String preventhorizontal() {
        String player = "x";
        boolean found = false;
        int count = 0;
        String block = "";
        for (int i = 0; i < ROWS; i++) {
            for (int j = 0; j < COLUMNS; j++) {
                if (board[i][j] == player) {
                    count++;
                } else if (board[i][j] == " ") {
                    block = "Block: " + i + " " + j;
                }
            }
            if (count == 2) {
                found = true;
                return block;
            } else {
                count = 0;
            }

        }
        return "";
    }

    public static String preventvertical() {
        String player = "x";
        boolean found = false;
        int count = 0;
        String block = "";
        for (int j = 0; j < COLUMNS; j++) {
            for (int i = 0; i < ROWS; i++) {
                if (board[i][j] == player) {
                    count++;
                } else if (board[i][j] == " ") {
                    block = "Block: " + i + " " + j;
                }
            }
            if (count == 2) {
                found = true;
                return block;
            } else {
                count = 0;
            }

        }
        return "";
    }

    public static int[] nextMove(String player) {
        int counter = 0;
        int pos[] = new int[18];
        for (int i = 0; i < 18; i++) {
            pos[i] = -1;
        }

        /* lucky position in the center of board*/
        if (board[1][1] == " ") {
            return new int[]{1, 1};
        }

        /* choose available move */
        for (int i = 0; i < 3; i++) {
            for (int j = 0; j < 3; j++) {
                if (board[i][j] == " ") {
                    pos[counter] = i;
                }
                pos[counter + 1] = j;
                counter = counter + 2;
            }
        }
        return pos;
    }

    public boolean checkWinner(String player) {
        if (checkDiagL(player)) {
            return true;
        } else if (checkDiagR(player)) {
            return true;
        } else if (checkHorizontal(player)) {
            return true;
        } else if (checkVertical(player)) {
            return true;
        } else {
            return false;
        }
    }

    public static String preventAll() {
        String block = preventdiagonalsLeft();

        if (block.equals("")) {
            block = preventdiagonalsRight();
            if (block.equals("")) {
                block = preventhorizontal();
                if (block.equals("")) {
                    block = preventvertical();
                }
            }
        }

        return block;

    }

    /**creates a string representation of the board
     * @return the string representation
     */
    public String toString() {
        String r = "";
        for (int i = 0; i < ROWS; i++) {
            for (int j = 0; j < COLUMNS; j++) {
                r += board[i][j];
                if (j < COLUMNS - 1) {
                    r += "|";
                }
            }
            r += "\n";
            if (i < ROWS - 1) {
                for (int j = 0; j < (COLUMNS * 2 - 1); j++) {
                    r += "-";
                }
                r += "\n";
            }
        }
        return r;
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        String player = "x";
        Tictactoe1 game = new Tictactoe1();
        boolean done = false;
        System.out.println(game.toString());
        while (!done) {

            int row = 0, column = 0;
            if (player.equals("o")) {
                nextMove("o");
                preventAll();
                

            } else {
                System.out.print("Row for " + player + " (-1 to exit): ");
                row = in.nextInt();
                if (row < 0) {
                    done = true;
                    break;
                } else {
                    System.out.print("Column for " + player + ": ");
                    column = in.nextInt();
                }
            }
            if (game.set(row, column, player).equals(player)) {
                System.out.println(game.toString());

                if (game.checkWinner(player)) {
                    System.out.println("Result: The Winner is " + player);
                    break;
                }

                if (player.equals("x")) {
                    player = "o";
                } else {
                    player = "x";
                }
            } else {
                System.out.println("Position selected!");
            }

        }
    }
}
I am looking for your reply