Tic-Tac-Toe Array Help

[Jacqueline Turof]

I'm working on creating a program where I can run two different games. I've just started and I'm stuck on just creating a tic-tac-toe board.
When I test to make sure that the board is set up properly it comes back as null. I'm obviously not setting my values for my array properly and was hoping someone had some advice. Thanks in advance!

import java.util.Arrays;


public class Board {
	public  int [][] board;
		public  Board(){
		int [][] board=	new int[3][3];
		for (int i=0;i<board.length;i++)
			for (int j=0; j<board.length;j++)
				board [i][j]=1;
		}
				
		    
		public  int [][] getboard()
		{
		return board;
		
		 }


}

import java.util.Arrays;
import java.util.Scanner;
public class Games {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		/*Setting up our menu. Prompting the user and setting our gameChoice to the user's input
		 * A bunch of if/else statements to deal with user input.
		 * Choice 1=guess the number
		 * Choice 2=tic tac toe
		 * If the user input any other type of data they will receive any error
		 * message.
		 * 
		 */
		System.out.println("Welcome to the games menu!\n Please choose your game option.\n"
            + " Press 1 to play guess the number or Press 2 to play tic tac toe.");
		// trying to create a new board object and test it and print it out
		 
 
		Board tictactoe=new Board();
		System.out.println(tictactoe.getboard());
		
		Scanner userChoice= new Scanner(System.in);
		int gameChoice=userChoice.nextInt();
		
		if (gameChoice==1){
		
		GuessGame UserGame=new GuessGame();
		}
		
		if(gameChoice==2){
			
			
			
		}
		
		else {
			System.out.println("Please enter a 1 to play guess the number or a 2 for tic tac toe.");
		}
		

		
	}

}

[Campbell Ritchie]

I added code tags, which you should always use, and also broke some of those long lines, and it looks a lot better. You still have too many blank lines, and you shouldn’t use the tab key for indenting.

Start by designing one game, and you can add other games later. Start designing from the centre and work out towards the periphery, but you code the other way: periphery first. Start by designing boards, maybe, and how you put circles and ×s on it.
Also search this forum; somebody else has a similar problem right now.

Also check that you are not declaring the same thing as a field and as a local variable. Why is your board using ints? You only ever use O/× so why ints?

[Jacqueline Turof]

So I've made some changes to my code and I am throwing a NullPointerException and can't figure out what I'm doing wrong.

For my code part of the requirements are that I create a board by making a multidimensional array and that I create a method with the header public String currentBoard() that returns the state of the board as a multi line String. Here is my code so far.

public class Board{

//declaring the board array and setting to type string

String [][]board;

//declaring our string lines for the currentBoard method

String line1= board[0][0]+ board [0][1]+board [0][2];
String line2= board [1][0]+board [1][1]+ board [1][2];
String line3= board [2][0]+ board[2][1]+ board [2][2];

//creating the Board()method to create a board that is a 2 dimensional array of strings

public Board(){
	String [][] board= new String [3][3];
	for (int i=0; i<board.length;i++){
		for (int j=0; j<board[i].length;j++){
			board [i][j]= "-";
		}}
	}

//creating a currentBoard() method to return the values of strings line1,line2, and line3		

public String currentBoard(){
	return (line1+"\n"+line2+"\n"+line3);
	
}


}

I have a checking class with a main method so that I can make sure things are working as they should.

public class Checking {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Board myBoard= new Board();
		System.out.println(myBoard.currentBoard());

	}

}

Any one have any ideas why I'm getting the error NullPointerException? Any help is appreciated!!!

[Jeff Verdegan]

Jacqueline Turof wrote:Any one have any ideas why I'm getting the error NullPointerException?

Because you're doing something equivalent to this:

Foo foo = null;
foo.someMethod();

If you want more help, you'll have to indicate clearly which line is causing the exception.

However, NPEs are among the easiest to diagnose and fix. The stack trace tells you exactly which line it's on, and even what the sequence of method calls is that got you there. Look at that line, see which references you're dereferencing, then work backwards to find which one is null. If you can't figure out which one by looking at the code, then add a bunch of print statements right before the offending line to see what's null.

Any help is appreciated!!!

Please don't shout.

[fred rosenberger]

a line like this:
String [][] board= new String [3][3];

creates an array, but it has nothing in it.

Also..remember that java doesn't have multi-dimensional arrays. it has arrays that hold objects - and those objects can be arrays.

So, after this line, you have an array that can hold three things (which have to be arrays of String), but those things don't exist yet. So you can't call a method on them.

[Jacqueline Turof]

fred rosenberger wrote:a line like this:
String [][] board= new String [3][3];

creates an array, but it has nothing in it.

Also..remember that java doesn't have multi-dimensional arrays. it has arrays that hold objects - and those objects can be arrays.

So, after this line, you have an array that can hold three things (which have to be arrays of String), but those things don't exist yet. So you can't call a method on them.

I thought I was filling the the array with the board [i][j]= "-"; statement? Thanks for the responses, they've been very informative.

[fred rosenberger]

public Board(){  
    String [][] board= new String [3][3];  
    for (int i=0; i<board.length;i++){  
        for (int j=0; j><board[i].length;j++){  
            board [i][j]= "-";  
        }}  
    }  

Do you actually get to the "board [i][j]= "-"; " line? I would think (and this is a guess) that you get the NPE on line 4 here. you are trying to get the length of an array that doesn't exist.>

[Jacqueline Turof]

fred rosenberger wrote:

public Board(){  
    String [][] board= new String [3][3];  
    for (int i=0; i<board.length;i++){  
        for (int j=0; j><board[i].length;j++){  
            board [i][j]= "-";  
        }}  
    }  

Do you actually get to the "board [i][j]= "-"; " line? I would think (and this is a guess) that you get the NPE on line 4 here. you are trying to get the length of an array that doesn't exist.>

Thank you for all your help. I was finally able to get it working.

[Jacqueline Turof]

So, I'm back. I've been able to create a board object, but now I'm having a new problem. I'm trying to write a play() method using a board object. I am unable to set up a loop that checks for a win. I've added println statements in the program trying to check the loop and see how its actually working, but I still can't tell what is going on. The reason the loops are set up differently for an X horizontal win was for diagnostic purposes. None of the those testing 1,2,3 print ln statements printed to the console and the loops never ended. If anyone has any advice or insight it would be greatly appreciated. Thanks in advance.

import java.util.Scanner;
public class Board{


	
//declaring the board array and setting to type string
static private String [][]board;
	
public Board(String[][]x){
	
board=x;
}


//creating a currentBoard() method to return the values of strings line1,line2, and line3		
public String currentBoard(){
	
	//declaring our string lines for the currentBoard method
	String line1= board[0][0]+ board [0][1]+board [0][2];
	String line2= board [1][0]+board [1][1]+ board [1][2];
	String line3= board [2][0]+ board[2][1]+ board [2][2];
	
	return (line1+"\n"+line2+"\n"+line3);
}
	

	public  void swapX(String[][]x,int a){
		
		if (a==1){
			x[0][0]="[X]";}
		if (a==2){
			x[0][1]="[X]";
		}
		if (a==3){
			x[0][2]="[X]";
		}
		if (a==4){
			x[1][0]="[X]";
		}
		if (a==5){
			x[1][1]="[X]";
		}
		if (a==6){
			x[1][2]="[X]";
		}
		if (a==7){
			x[2][0]="[X]";
		}
		if (a==8){
			x[2][1]="[X]";
		}
		if (a==9){
			x[2][2]="[X]";
		}

	}
	public void swapO(String[][]x,int a){
		if (a==1){
			x[0][0]="[O]";}
		if (a==2){
			x[0][1]="[O]";
		}
		if (a==3){
			x[0][2]="[O]";
		}
		if (a==4){
			x[1][0]="[O]";
		}
		if (a==5){
			x[1][1]="[O]";
		}
		if (a==6){
			x[1][2]="[O]";
		}
		if (a==7){
			x[2][0]="[O]";
		}
		if (a==8){
			x[2][1]="[O]";
		}
		if (a==9){
			x[2][2]="[O]";
		}
	}
public void play(){
String [][]boardIntial={{"[1]","[2]","[3]"},{"[4]","[5]","[6]"},{"[7]","[8]","[9]"}};//initial board
Board myBoard=new Board(boardIntial);
boolean win=false;
Scanner input=new Scanner(System.in);
int turnCounter=0;
int playerX=0;
int playerO=0;

while(win==false)
{

   //checking for and X win horizontially
	System.out.println("Testing,1,2,3.");
	    if (boardIntial[0][0].equals("[1]")&& boardIntial[0][1].equals("[2]")&& boardIntial[0][2].equals("[3]")){
		win=true;
		
		}
	if (boardIntial[1][0].equals("[X]")&& boardIntial[1][1].equals("[X]")&& boardIntial[1][2].equals("[X]")){
		win=true;
		}
	if (boardIntial[2][0].equals("[X]")&& boardIntial[2][1].equals("[X]")&& boardIntial[2][2].equals("[X]")){
		win=true;
		}
	
	
	

    


 ++turnCounter;//set turn counter to add 1 every iteration
 System.out.println(myBoard.currentBoard());
 System.out.println("What the hell is going on?");
 
//checking for X win vertically
 if(win==false){
	 System.out.println("testing 1, 2, 3");
	
	if (boardIntial[0][0].equals("[1]")&& boardIntial[1][0].equals("[2]")&& boardIntial[2][0].equals("[3]")){
		
		win=true;
		}
	if (boardIntial[0][1].equals("[X]")&& boardIntial[1][1].equals("[X]")&& boardIntial[2][1].equals("[X]")){
		win=true;
		}
	if (boardIntial[0][2].equals("[X]")&& boardIntial[1][2].equals("[X]")&& boardIntial[2][2].equals("[X]")){
		win=true;
		}
	
	//checking for X win diagonally
	
	if (boardIntial[0][0].equals("[X]")&& boardIntial[1][1].equals("[X]")&& boardIntial[2][2].equals("[X]")){
		win=true;
		}
	if (boardIntial[0][2].equals("[X]")&& boardIntial[1][1].equals("[X]")&& boardIntial[2][0].equals("[X]")){
		win=true;
		}

     }

 
 if ((turnCounter%2)!=0)
 {
	 
	 System.out.println("Player 1 you are X! Please pick a square.");
	 playerX=input.nextInt();
	 swapX(boardIntial,playerX);
	 
	 
	
 
	 }
 
 

 
 if ((turnCounter%2)==0)
 {
	 System.out.println("Player 2 you are O! Please pick a square."); 
	 playerO=input.nextInt();
	 swapO(boardIntial,playerO);
	 
	
	//checking for O win horizontially
 	
 	if (boardIntial[0][0].equals("O")&& boardIntial[0][1].equals("O")&& boardIntial[0][2].equals("O")){
 		win=true;
 		}
 	if (boardIntial[1][0].equals("O")&& boardIntial[1][1].equals("O")&& boardIntial[1][2].equals("O")){
 		win=true;
 		}
 	if (boardIntial[2][0].equals("O")&& boardIntial[2][1].equals("O")&& boardIntial[2][2].equals("O")){
 		win=true;
 		}
 	
 	//checking for an O win vertically
	
	if (boardIntial[0][0].equals("O")&& boardIntial[1][0].equals("O")&& boardIntial[2][0].equals("O")){
		win=true;
		}
	if (boardIntial[0][1].equals("O")&& boardIntial[1][1].equals("O")&& boardIntial[2][1].equals("O")){
		win=true;
		}
	if (boardIntial[0][2].equals("O")&& boardIntial[1][2].equals("O")&& boardIntial[2][2].equals("O")){
		win=true;
		}
	
	//checking for an O win diagonally
	
	if (boardIntial[0][0].equals("O")&& boardIntial[1][1].equals("O")&& boardIntial[2][2].equals("O")){
		win=true;
		}
	if (boardIntial[0][2].equals("O")&& boardIntial[1][1].equals("O")&& boardIntial[2][0].equals("O")){
		win=true;
		}}
	
	
}








}
}



    
		

[fred rosenberger]

generally, you don't need to do this:

if (win == false)

you can just do

if (!win)

if your code isn't entering loops you think it should, put in more system.outprintln statements. Print what "win" is just before your if-test