Problems with java - error NullPointerException

Question

I was working on recreation of the 1970 "Game of Life". But I keep on running into a NullPointerException Error. The simulation works on a 2d board, so I made a 2d array of objects of the object, boardSpace. I have no idea why the NullPointerException happens, all other forums have told me that I need to initialize everything properly. I feel like I have. Here's the code:

import java.util.Scanner;

class simulation{

public static void main(String[] args){
    boardSpace[][] board = new boardSpace[30][25];

    for (int a = 0; a < 5; a++){    //All these set initial values
        for (int b = 0; b < 25; b++){
            board[a][b] = new boardSpace(a, b);
            board[a][b].state = false;
        }
    }

    for (int c = 5; c < 10; c++){
        for (int b = 0; b < 25; b++){
            if (b % 2 == 1){
                board[c][b] = new boardSpace(c, b);
                board[c][b].state = false;
            }else{
                board[c][b] = new boardSpace(c, b);
                board[c][b].state = true;
            }
        }
    }

    for (int d = 10; d < 15; d++){
        for (int b = 0; b < 25; b++){
            if (b % 2 == 1){
                board[d][b] = new boardSpace(d, b);
                board[d][b].state = true;
            }else{
                board[d][b] = new boardSpace(d, b);
                board[d][b].state = false;
            }
        }
    }

    for (int e = 15; e < 20; e++){
        for (int b = 0; b < 25; b++){
            if (b % 2 == 1){
                board[e][b] = new boardSpace(e, b);
                board[e][b].state = false;
            }else{
                board[e][b] = new boardSpace(e, b);
                board[e][b].state = true;
            }
        }
    }

    for (int f = 20; f < 25; f++){
        for (int b = 0; b < 25; b++){
            board[f][b] = new boardSpace(f, b);
            board[f][b].state = false;
        }
    }

    System.out.println("Let's begin");

    Scanner input = new Scanner(System.in);
    double command = 100.0;

    while (command != 1){
        if (command == 100.0){
            for (int x = 0; x < 30; x++){
                for (int y = 0; y < 25; y++){
                    printer(board);                    //line 69
                    board[x][y].checker(board);
                }
            }
            printer(board);
            for (int x = 0; x < 30; x++){
                for (int y = 0; y < 25; y++){
                    board[x][y].numNeighbors = 0;
                }
            }
        }
        System.out.println("0 to stop simulation or 100.0 for next gen");
        command = input.nextDouble();
    }
    }

public static void printer(boardSpace[][] grid){
    for (int v = 0; v < 30; v++){
        for (int w = 0; w < 25; w++){
            if (grid[v][w].state == true){    //line 88
                if (w == 24){
                    System.out.println("X");
                }else{
                    System.out.print("X");
                }
            }else{ 
                if (w == 24){
                    System.out.println("-");
                }else{
                    System.out.print("-");
                }
            }
        }
    }
}
}


class boardSpace{
    int xValue; //recognizes where the thing is
    int yValue;
    boolean state;  //sees whether the space has a thing in it or not
    int numNeighbors;

public boardSpace(int xPos, int yPos){
    xValue = xPos;
    yValue = yPos;
}

public void checker(boardSpace[][] grid){   //checks for neighbours 
    if (grid[xValue - 1][yValue - 1].state == true){
        numNeighbors++;
    }
    if (grid[xValue - 1][yValue].state == true){
        numNeighbors++;
    }
    if (grid[xValue - 1][yValue + 1].state == true){
        numNeighbors++;
    }
    if (grid[xValue][yValue - 1].state == true){
        numNeighbors++;
    }
    if (grid[xValue][yValue + 1].state == true){
        numNeighbors++;
    }
    if (grid[xValue + 1][yValue - 1].state == true){
        numNeighbors++;
    }
    if (grid[xValue + 1][yValue].state == true){
        numNeighbors++;
    }
    if (grid[xValue + 1][yValue + 1].state == true){
        numNeighbors++;
    }
}

public void stateChanger(){
    if (numNeighbors <= 1){
        state = false;
    }else if(numNeighbors == 2){
        state = state;
    }else if(numNeighbors == 3){
        state = true;
    }else if(numNeighbors >= 4){
        state = false;
    }
}
}

Then the output shows the beginning position of the board, which is correct, but it is followed by a message saying that at lines 88 and 69 (marked on code as comments) there is a NullPointerException error:

Let's begin
-------------------------
-------------------------
-------------------------
-------------------------
-------------------------
X-X-X-X-X-X-X-X-X-X-X-X-X
X-X-X-X-X-X-X-X-X-X-X-X-X
X-X-X-X-X-X-X-X-X-X-X-X-X
X-X-X-X-X-X-X-X-X-X-X-X-X
X-X-X-X-X-X-X-X-X-X-X-X-X
-X-X-X-X-X-X-X-X-X-X-X-X-
-X-X-X-X-X-X-X-X-X-X-X-X-
-X-X-X-X-X-X-X-X-X-X-X-X-
-X-X-X-X-X-X-X-X-X-X-X-X-
-X-X-X-X-X-X-X-X-X-X-X-X-
X-X-X-X-X-X-X-X-X-X-X-X-X
X-X-X-X-X-X-X-X-X-X-X-X-X
X-X-X-X-X-X-X-X-X-X-X-X-X
X-X-X-X-X-X-X-X-X-X-X-X-X
X-X-X-X-X-X-X-X-X-X-X-X-X
-------------------------
-------------------------
-------------------------
-------------------------
-------------------------
Exception in thread "main" java.lang.NullPointerException
        at simulation.printer(sfAssign1.java:88)
        at simulation.main(sfAssign1.java:69)

I'm sorry if this is a really obvious mistake I'm making. I'm extremely new to Java programming...