I can't figure out why I'm getting a Null Pointer Exception

Question

I'm writing a program that calls Bingo numbers. I got that part of the program to work but when I started adding Swing I kept getting a Null Pointer Exception and I don't know how to fix it. The Exception happens on line 15 of class Panel (g = image.getGraphics();). Here is the code for my classes. I'm still not finished with the program and I can't finish it until I know that this issue is resolved.
package Graphics;
import java.awt.Graphics;
import javax.swing.JFrame;
public class DrawFrame extends JFrame{
     public Panel panel;
     public DrawFrame(int x, int y, String s) {
          super(s);
          this.setBounds(0, 0, x, y);
          this.setResizable(false);
          this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
          this.setPreferredSize(getSize());
          panel = this.getPanel();
          this.getContentPane().add(panel);
          panel.init();
          this.setVisible(true);
     public Graphics getGraphicsEnvironment(){
          return panel.getGraphicsEnvironment();
     Panel getPanel(){
          return new Panel();
package Graphics;
import javax.swing.JPanel;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Image;
public class Panel extends JPanel{
     Graphics g;
     Image image;
     public void init() {
          image = this.createImage(this.getWidth(), this.getHeight());
          g = image.getGraphics();
          g.setColor(Color.white);
          g.fillRect(0, 0, this.getWidth(), this.getHeight());
     Graphics getGraphicsEnvironment() {
          return g;
     public void paint(Graphics graph) {
          if (graph == null)
               return;
          if (image == null) {
               return;
          graph.drawImage(image, 0, 0, this);
package Graphics;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
public class Keys extends KeyAdapter{
public int keyPressed; //creates a variable keyPressed that stores an integer
public void keyPressed(KeyEvent e) { //creates a KeyEvent from a KeyListner
          keyPressed = e.getKeyCode(); //gets the key from the keyboard
import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.event.KeyEvent;
import Graphics.*;
public class Bingo {
     static Ball balls[][] = new Ball[5][15]; //creates a 2D 5 by 15 array
     public static void main(String[] args) {
          DrawFrame frame = new DrawFrame(1500, 500, "Welcome to the automated Bingo Caller."); //creates instance of DrawFrame that is 1000 pixels wide and 500 pixels high
          Graphics g = frame.getGraphicsEnvironment(); //calls the getGraphicsEnvironment method in the DrawFrame class
          Keys key = new Keys(); //creates instance of the Key class
          frame.addKeyListener(key); //adds a KeyListener called Key
          for (int x = 0; x < 5; x++) { //fills rows
               for (int y = 0; y < 15; y++) { //fills columns
                    balls[x][y] = new Ball(x, y+1); //fills array
          frame.pack(); //adjusts the size of the frame so everything fits
          g.setColor(Color.black); //sets the font color to black
          g.setFont(new Font("MonoSpace", Font.PLAIN, 20)); //creates new font
          for(int y=0;y<balls.length;y++){ //draws all possible balls
               g.drawString(balls[y][0].s, 0, y*100); //draws numbers
               for(int x=0;x<balls[y].length;x++){ //draws all possible balls
                    g.drawString(balls[y][x].toString(), (x+1)*100, y*100); //draws letters
          do {
               frame.repaint(); //repaints the balls when one is called
               int x, y; //sets variables x and y as integers
               boolean exit; //sets a boolean to the exit variable
               do {
                    exit = false; //exit is set to false
                    x = (int)(Math.random() * 5); //picks a random number between 0 and 4 and stores it as x
                    y = (int)(Math.random() * 15); //picks a random number between 0 and 14 stores it as y
                    if (!balls[x][y].called) { //checks to see if a value is called
                         exit = true; //changes exit to true if it wasn't called
                         balls[x][y].called = true; //sets called in the Ball class to true if it wasn't called
                         System.out.println(balls[x][y]); //prints value
               } while (!exit); //if exit is false, returns to top of loop
               int count = 0; //sets a count for the number of balls called
               for(int z=0;z<balls.length;z++){ //looks at balls
                    g.setColor(Color.black); //displays in black
                    g.drawString(balls[z][0].s, 0, z*100); //draws balls as a string
                    for(int a=0;a<balls[z].length;a++){ //looks at all balls
                         if (balls[z][a].called){ //if a ball is called
                              g.setColor(Color.red); //change color to red
                              count++; //increments count
                         } else {
                              g.setColor(Color.black); //if it isn't called stay black
                         g.drawString(balls[z][a].toString(), (a+1)*100, y*100); //draws balls as string
               do {
                    if (key.keyPressed == KeyEvent.VK_R||count==5*15) { //if R is pressed or count = 5*15
                         count=5*15; //changes count to 5*15
                         for(int z=0;z<balls.length;z++){ //recreates rows
                              g.setColor(Color.black); //sets color to black
                              g.drawString(balls[z][0].s, 0, z*100); //redraws rows
                              for(int a=0;a<balls[z].length;a++){ //recreates columns
                                   balls[z][a] = new Ball(z, a+1); //fills array
                                   g.drawString(balls[z][a].toString(), (a+1)*100, z*100); //redraws columns
               } while (key.keyPressed!=KeyEvent.VK_ENTER || count == 5 * 15); //determines if the key was pressed or counter is 5*15s
          } while (key.keyPressed == KeyEvent.VK_ENTER);
public class Ball {
     String s; //initiates s that can store data type String
     int i; //initiates i that can store data as type integer
     boolean called = false; //initiates called as a boolean value and sets it to false
     public Ball(int x, int y) {
          i = (x * 15) + y; //stores number as i to be passed to be printed
          switch (x) { //based on x value chooses letter
          case 0:
               s = "B";
               break;
          case 1:
               s = "I";
               break;
          case 2:
               s = "N";
               break;
          case 3:
               s = "G";
               break;
          case 4:
               s = "O";
     public String toString() { //overrides toString method, converts answer to String
          return s + " " + i; //returns to class bingo s and i
}

Answer 1

The javadoc of createImage() states that "The return value may be null if the component is not displayable."
Not sure, but it may be that you need to call init() after this.setVisible(true).