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While buttons are changing color every second, how do I make the button I press stop while the other buttons continue switching colors?

I am creating a grid of 4 by 2 buttons and I want them to continuously change color. A button will stop changing colors once I press it. I have having trouble figuring how to make that one button stop changing colors if I press on it and have other buttons to continuously change color. If I press another button, that button stops changing color as well.
public class Hw1 extends JPanel {
static JFrame jf;
static JPanel jp;
static JButton jb;
public static void main(String[] args) {
jf = new JFrame("Hello World!");
int xAxis = 500;
int yAxis = 300;
jf.setSize(xAxis, yAxis);
jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
jp = new JPanel();
int num = 8;
JButton[] buttonList = new JButton[num];
int count = 0;
// creates buttons and initially assigns random color
for(int i = 0; i < 2 ; i++){
for(int j = 0; j < 4; j++){
jb = new JButton("press me!");
jb.setBounds(i * (xAxis/2), j * (yAxis/4), xAxis/2, yAxis/4);
jb.setVisible(true);
jb.setOpaque(true);
int primeR = (int)(Math.random() * 255+ 0);
int primeG = (int)(Math.random() * 255 + 0);
int primeB = (int)(Math.random() * 255 + 0);
Color random = new Color(primeR, primeG, primeB);
jb.setBackground(random);
// adds action listener to each button aka checks if button is pressed
jb.addActionListener(new ActionListener(){
// action if button is pressed
//if pressed change stop changing colors
public void actionPerformed(ActionEvent ae) {
JButton theButton = (JButton)ae.getSource();
theButton.setBackground(random);
}
});
buttonList[count] = jb;
count++;
jp.add(jb);
}
}
jf.add(jp);
jf.setVisible(true);
for (int k = 0; k < buttonList.length; k++) {
new Thread(){
public void run(){
while(true){
try {
sleep(1000);
}
catch (InterruptedException ex) {
}
for (int i = 0; i < buttonList.length; i++) {
int primeR = (int)(Math.random() * 255);
int primeG = (int)(Math.random() * 255);
int primeB = (int)(Math.random() * 255);
Color random = new Color(primeR, primeG, primeB);
buttonList[i].setBackground(random);
}
}
}
}.start();
}
}
}

you need to keep state of button.
If you have grid of 4 button, make an array of it's state buttonState = new Boolean[2][2]
when button on position x,y is pressed, set value of [x][y] to true. check buttonState before changing color of button.
OR
Overwrite JButton and add bolean field pressed to it, and set it to true in onClick, and based on that value change or not change color

Counter loop in Java

I have created a game where the player collects pods on the game board. I need to make an evasive maneuver so that after five turns when the player is one space away from the pod, the pod will transport 10 spaces away from the player. I believe my counter is not working and that is why the evasive maneuver is not working.
public class Pod {
int podPositionX;
int podPositionY;
String podDirection;
int layoutWidth;
int layoutHeight;
boolean podVisable = true;
int playerX;
int playerY;
int count = 0;
public Pod(int x, int y, String direction, int width, int height){
podPositionX = x;
podPositionY = y;
podDirection = direction;
layoutWidth = width;
layoutHeight = height;
count=count+1;
}
//Inspector Methods?
// Will get the the pods positon and will return it
public int getX()
{
return podPositionX;
}
//This method returns the current Y coordinate of the pod.
public int getY()
{
return podPositionY;
}
//This method returns true if the pod is visible, false otherwise. Once the
//pod has been caught, it should always return false.
public boolean isVisible(){
if (playerX == podPositionX && playerY == podPositionY && podVisable == true){
podVisable = false;}
return podVisable;
}
// to move pod diagonally across screen//
public void move(){
//Calling invasive methods!!
while (count>5 && count < 100){
podPositionX=transportX();
podPositionY=transportY();
}
/****************** To make pod move **************/
if (podDirection.equals("NW")|| podDirection.equals("NE")){
podPositionY = podPositionY + 1;}
if (podDirection.equals("SW")|| podDirection.equals("SE")){
podPositionY = podPositionY-1;}
if (podDirection.equals("NE")|| podDirection.equals("SE")){
podPositionX = podPositionX+1;}
if(podDirection.equals("NW")|| podDirection.equals("SW")){
podPositionX = podPositionX-1;}
/****************To make Pod bounce off wall******************/
//make pod bounce off left wall
if (podPositionX <= 1){
if (podDirection.equals("SW")){
podDirection = "SE";}
if (podDirection.equals("NW")){
podDirection = "NE";}
}
//make pod bounce off top
if (podPositionY >= layoutHeight-1){
if (podDirection.equals("NW")){
podDirection = "SW";}
if (podDirection.equals("NE")){
podDirection = "SE";}
}
//make pod bounce off right wall
if (podPositionX >= layoutWidth-1){
if (podDirection.equals("NE")){
podDirection = "NW";}
if (podDirection.equals("SE" )){
podDirection = "SW";}
}
//make pod bounce off bottom wall
if (podPositionY <= 1){
if (podDirection.equals("SW")){
podDirection = "NW";}
if (podDirection.equals("SE")){
podDirection = "NE";}
}
}
// to get player x and y positions
public void playerAt(int x, int y){
playerX = x;
playerY = y;
}
//envasive maneuver so that after 5 turns the pod can be transported away from the player if it is 1 spot away from the player.
//then the count is set to 100 so it will exit the loop and not be able to transport the pod again.
public int transportX(){
if (podPositionX == playerX -1 || podPositionX == playerX +1){
podPositionX= playerX +10;
count = 100;}
return podPositionX;
}
public int transportY(){
if (podPositionY == playerY -1 || podPositionY == playerY +1){
podPositionY= playerY +10;
count=100;}
return podPositionY;
}
}
the code my teacher provided us. Can no be touched so i can not put a counter in this file.
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class Project1 extends JFrame implements ActionListener {
// Member variables for visual objects.
private JLabel[][] board; // 2D array of labels. Displays either # for player,
// * for pod, or empty space
private JButton northButton, // player presses to move up
southButton, // player presses to move down
eastButton, // player presses to move right
westButton; // player presses to move left
// Current width and height of board (will make static later).
private int width = 15;
private int height = 9;
// Current location of player
private int playerX = 7;
private int playerY = 4;
// Pod object stored in array for efficiency
private Pod[] pods;
int podCount = 4;
public Project1() {
// Construct a panel to put the board on and another for the buttons
JPanel boardPanel = new JPanel(new GridLayout(height, width));
JPanel buttonPanel = new JPanel(new GridLayout(1, 4));
// Use a loop to construct the array of labels, adding each to the
// board panel as it is constructed. Note that we create this in
// "row major" fashion by making the y-coordinate the major
// coordinate. We also make sure that increasing y means going "up"
// by building the rows in revers order.
board = new JLabel[height][width];
for (int y = height-1; y >= 0; y--) {
for (int x = 0; x < width; x++) {
// Construct a label to represent the tile at (x, y)
board[y][x] = new JLabel(" ", JLabel.CENTER);
// Add it to the 2D array of labels representing the visible board
boardPanel.add(board[y][x]);
}
}
// Construct the buttons, register to listen for their events,
// and add them to the button panel
northButton = new JButton("N");
southButton = new JButton("S");
eastButton = new JButton("E");
westButton = new JButton("W");
// Listen for events on each button
northButton.addActionListener(this);
southButton.addActionListener(this);
eastButton.addActionListener(this);
westButton.addActionListener(this);
// Add each to the panel of buttons
buttonPanel.add(northButton);
buttonPanel.add(southButton);
buttonPanel.add(eastButton);
buttonPanel.add(westButton);
// Add everything to a main panel attached to the content pane
JPanel mainPanel = new JPanel(new BorderLayout());
getContentPane().add(mainPanel);
mainPanel.add(boardPanel, BorderLayout.CENTER);
mainPanel.add(buttonPanel, BorderLayout.SOUTH);
// Size the app and make it visible
setSize(300, 200);
setVisible(true);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
// Auxiliary method to create game setup
createGame();
}
// Auxiliary method used to create board. Sets player, treasure, and walls.
public void createGame() {
// Construct array of Pod objects
pods = new Pod[podCount];
// Construct each Pod in the array, passing it its initial location,
// direction of movement, and the width and heigh of board. This will
// later be modified to be done at random.
pods[0] = new Pod(1, 5, "NE", width, height);
pods[1] = new Pod(2, 1, "SW", width, height);
pods[2] = new Pod(12, 2, "NW", width, height);
pods[3] = new Pod(13, 6, "SE", width, height);
// Call method to draw board
drawBoard();
}
// Auxiliary method to display player and pods in labels.
public void drawBoard() {
// "Erase" previous board by writing " " in each label
for (int y = 0; y < height; y++) {
for (int x = 0; x < width; x++) {
board[y][x].setText(" ");
}
}
// Get location of each pod and write * into that label. We only
// do this for pods not yet caught.
for (int p = 0; p < podCount; p++) {
if (pods[p].isVisible()) {
board[pods[p].getY()][pods[p].getX()].setText("*");
}
}
// Write the player onto the board.
board[playerY][playerX].setText("#");
}
public void actionPerformed(ActionEvent e) {
// Determine which button was pressed, and move player in that
// direction (making sure they don't leave the board).
if (e.getSource() == southButton && playerY > 0) {
playerY--;
}
if (e.getSource() == northButton && playerY < height-1) {
playerY++;
}
if (e.getSource() == eastButton && playerX < width-1) {
playerX++;
}
if (e.getSource() == westButton && playerX > 0) {
playerX--;
}
// Move the pods and notify the pods about player location.
for (int p = 0; p < podCount; p++) {
pods[p].move();
pods[p].playerAt(playerX, playerY);
}
// Redraw the board
drawBoard();
}
/**
* #param args the command line arguments
*/
public static void main(String[] args) {
Project1 a = new Project1();
}
}

I am looking at this quickly now. You said the problem is with the count variable. I see that you are incrementing it in the constructor i.e
public Pod(int, int, String, int, int){
count = count + 1;
}
why not put it in the move method. That way every time the move method is used the count variable will be incremented by one.
public void move(){
this.count++;
}
Also it is very hard to see exactly what you think your code is doing. I tried to run it and nothing happens. Sometimes it is good to print something to the console.

Finishing Keno Java code?

This is what I am having trouble with. I am making a Keno game out of a Crystals code I was given. So far, I have been able to choose 20 of the 80 and turn them red. However, I have the button set to when I press it it says "Game is a draw" and the window closes.
I am trying to put in a code where it will randomly draw 20 numbers without repeating, and then they turn yellow, however, if the CPU and the human match a number, it will turn green. I have no idea how to start this code or how to go about doing it. Here is what I have:
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
import java.util.*;
import java.lang.String;
public class Kenogame {
// constants
public static final int WIDTH = 4;
public static final int HEIGHT = 20;
public static final int INITIAL = 0;
public static final int RED = 1;
public static final int YELLOW = 3;
public static final int CHECKED = 4;
private int turn = RED; // to track which player should play next
private int[][] playerGrid; // to record each player's move
private int[][] shadowGrid; // to keep track of which atoms have been FOUND
private int[][] crystalGrid; // to extract a single crystal from playerGrid
private int row, column; // position of most recently added atom
private int lowX, lowY, highX, highY; // corner coordinates of current crystal
private int player1Score = 0;
private int player2Score = 0;
// GUI related fields
private JButton[] buttonArray;
// private JTextField scoreField1;
// private JTextField scoreField2;
// private JLabel labelRED; // Label "Red" on GUI
// private JLabel labelYELLOW; // Label "Yellow" on GUI
private JLabel labelTurn; // Label displays whose turn is next
private int numberToSelect = 20;
Kenogame() {
createGUIAndPlay();
}
private void createGUIAndPlay() {
final JFrame f = new JFrame();
// create the panels
JPanel topPanel = new JPanel(new BorderLayout());
JPanel buttonPanel = new JPanel(new GridLayout(WIDTH, HEIGHT));
JPanel labelPanel = new JPanel();
// represents the 2D grid of buttons on the GUI
buttonArray = new JButton[WIDTH * HEIGHT];
// stores the positions of atoms in both player's crystals
playerGrid = new int[WIDTH][HEIGHT];
// shadowGrid keeps track of which atoms have been found
shadowGrid = new int[WIDTH][HEIGHT];
// used to store a crystal to determine if it is a perfect crystal
crystalGrid = new int[WIDTH][HEIGHT];
JButton endGameButton = new JButton("Start Draw");
// labelRED = new JLabel("Red");
// scoreField1 = new JTextField(3);
// scoreField1.setEditable(false);
//labelYELLOW = new JLabel("Yellow");
labelTurn = new JLabel(Integer.toString(numberToSelect), Label.LEFT);
Dimension dim = labelTurn.getPreferredSize();
labelTurn.setPreferredSize(new Dimension(dim.width + 100, dim.height + 10));
// scoreField2 = new JTextField(3);
// scoreField2.setEditable(false);
// scoreField1.setText("0");
// scoreField2.setText("0");
// create the buttons on which players will make their moves
for (int i = 0; i < HEIGHT * WIDTH; i++) {
buttonArray[i] = new JButton(Integer.toString(i + 1));
buttonPanel.add(buttonArray[i]);
}
final Color buttColor = buttonArray[0].getBackground();
// add the action listener to the buttons
for (int i = 0; i < HEIGHT * WIDTH; i++) {
buttonArray[i].setActionCommand(Integer.toString(i));
buttonArray[i].addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
JButton button = (JButton) e.getSource();
if (button.getBackground() == Color.RED) {
button.setBackground(buttColor);
numberToSelect++;
} else {
if (numberToSelect > 0) {
button.setBackground(Color.RED);
numberToSelect--;
}
}
// button.setEnabled(false);
int buttonIndex = Integer.valueOf(button.getActionCommand());
row = buttonIndex / WIDTH;
column = buttonIndex % WIDTH;
// playMove();
labelTurn.setText(Integer.toString(numberToSelect));
// updateGUI();
}
});
}
endGameButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
String s;
// Need to add "ball draw here" for Keno
// 20 random numbers between 1 and 80
// each time a "ball" matches one selected on the Keno ticket add to a counter
// at end look up payout for the number of matches corresponding to the counter
if (player1Score > player2Score)
s = "RED wins the game";
else if (player1Score < player2Score)
s = "YELLOW wins the game";
else
s = "Game is a draw";
JOptionPane.showMessageDialog(f, s, "Game Over", JOptionPane.PLAIN_MESSAGE);
System.exit(1);
}
});
labelPanel.add(endGameButton);
labelPanel.add(labelTurn);
topPanel.add(labelPanel, BorderLayout.NORTH);
topPanel.add(buttonPanel, BorderLayout.CENTER);
f.add(topPanel);
f.setSize(1000, 400);
f.setTitle("Keno");
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.setVisible(true);
}
private void playMove() {
playerGrid[row][column] = turn;
if (turn == RED) {
turn = YELLOW;
} else {
turn = RED;
}
}
private void initialize() {
highX = highY = Integer.MIN_VALUE;
lowX = lowY = Integer.MAX_VALUE;
for (int row = 0; row < HEIGHT; row++)
for (int column = 0; column < WIDTH; column++) {
crystalGrid[row][column] = INITIAL;
}
}
public static void main(String[] args) {
new Keno();
}
}
// green for a match, yellow for a no-match.
I have 4 lines towards the bottom where I am supposed to insert the code. I would really appreciate it if someone could give me a hand on this.

To draw 20 non-repeating numbers, you can do the following:
put your 80 numbers in a collection.
shuffle the collection
the elements are now in random order and you can loop over the collection to get the first 20 elements.
If you give me more details on what you are stuck, I can provide further information.

Buttons in gameplay not displaying correct message

I am coding a minesweeper game. The buttons should display the numbers 0,1 or 2 when clicked to display how many mines are adjacent. I recently changed the layout to gridlayout and since then all I get when I click on a button is '...' with the exception of the discovery of a mine which changes the button to the bomb gif.
Can anyone tell me how to get the numbers back on click?
Here is the code to create the button Array:
JPanel gridPanel = new JPanel(new GridLayout(boardsize, boardsize));
buttons = new JButton[boardsize][boardsize];
mineBoard = new int[9][9];
for (int a = 0; a < boardsize; a++)
for (int b = 0; b < boardsize; b++) {
buttons[a][b] = new JButton("");
gridPanel.add(buttons[a][b]);
buttons[a][b].addMouseListener(new MouseListener(a,b));
setx(a);
sety(b);
settried(false);
setmine(false);
}
contentPane.add(gridPanel, BorderLayout.CENTER);
When the user clicks a button:
// This method takes in an x and y value and defines what should happen when the user clicks there.
public void click(int row, int col) {
if(mineBoard[row][col] == Mine) {
buttons[row][col].setIcon( new ImageIcon( "images/bomb.gif" ) );
lose();
} else {
score += 1;
updatescore();
buttons[row][col].setText("" + numAdjMines(mineBoard, row, col));
mineBoard[row][col] = UncoveredEmpty;
buttons[row][col].setText(Character.toString(getUserChar(mineBoard[row][col])));
if(numAdjMines(mineBoard, row, col) == Empty) {
for(int dr = -1; dr <= 1; dr ++) {
for(int dc = -1; dc <= 1; dc++) {
if(row+dr >= 1 && row+dr < 10 &&
col+dc >= 1 && col+dc < 10) {
if(mineBoard[row+dr][col+dc] == Empty) {
click(row+dr,col+dc);
}
}
}
}
}
}
}
MouseLister Class:
//ACTION WHEN USER CLICKS ON A BUTTON
private class MouseListener extends MouseAdapter {
private int x = 0;
private int y = 0;
public MouseListener(int row, int col) {
this.x = row;
int i = 0;
this.y = col;
}
public void mouseClicked(MouseEvent e) {
if(e.getButton() == MouseEvent.BUTTON1) {
if((mineBoard[x][y] == Empty) && (Game.this.gamegoing == true)) {
Game.this.click(x, y);
} else if(mineBoard[x][y] == Mine) {
buttons[x][y].setIcon( new ImageIcon( "images/bomb.gif" ) );
Game.this.lose();
}} else if(e.getButton() == MouseEvent.BUTTON3) {
Game.this.buttons[x][y].setText("F");
}
}
}

You can try to add a few spaces to your default text of the button, something like that:
buttons[a][b] = new JButton(" ");
Or you can try to pack your window after you set the text on the button.

When a JButton only dislays dots it means that there is not enough space to write down the tekst.
So the solution would be to tell Gridlayout to make the buttons larger.
I'd recomend that you find test your game with a very big windows and then try to find the point where your windows is big enough that Gridlayout en JButton agree that the tekst can be placed.
Then you should see how big your buttons are at that point and then either:
Tell GridLayout how big your buttons should be (by calling setPrefferedSize() that should work)
Or use another layout manager that does not give you this problem.
P.S. A your bomb picture appear because picures are handled in a different way. They are always displayed I belive.
I hope this solves it for you.

Convert Java Applet to Application

So I followed a free manual instructing how to write Asteroids in Java, and it runs great. I would like to add it into a program so I can call it, run it for a time, and then have it return an int. The program I'm making is an application, and I've been searching for a while trying and failing, figuring out how to make make it run as an application. The stuff I've read here says I should do this:
public class Main extends JFrame {
public static void main(String[] args) {
AsteroidsGame game = new AsteroidsGame();
JFrame frame = new JFrame();
frame.setLayout(new GridLayout (1,1));
frame.add(game);
frame.setSize(500,500);
game.init();
game.start();
frame.setVisible(true);
}
}
But then I get an error
Exception in thread "main" java.lang.NullPointerException
at AsteroidsGame.init(AsteroidsGame.java:49)
at Main.main(Main.java:15)
which points me to the below for line 49, and my game.init() for line 15.
g = img.getGraphics();
Here's the code for the AsteroidsGame, I'm too tired to think anymore. I just need to get it to run as an application, any other code changes are irrelevant at this point. I know it's a lot of code but I'm hoping it's a simple something I've missed. Any help is greatly appreciated. Thank you!
import java.applet.*;
import java.awt.*;
import java.awt.event.*;
import java.util.Random;
public class AsteroidsGame extends Applet implements Runnable, KeyListener {
Thread thread;
Dimension dim;
Image img;
Graphics g;
long endTime, startTime, framePeriod;
Ship ship;
boolean paused; // True if the game is paused. Enter is the pause key
Shot[] shots;
int numShots;
boolean shooting;
Asteroid[] asteroids; // the array of asteroids
int numAsteroids; // the number of asteroids currently in the array
double astRadius, minAstVel, maxAstVel; // values used to create
// asteroids
int astNumHits, astNumSplit;
int level; // the current level number
int money;
double fuel;
Random rand = new Random();
public void init() {
resize(500, 500);
shots = new Shot[41]; // 41 is a shot's life period plus one.
// since at most one shot can be fired per frame,
// there will never be more than 41 shots if each one only
// lives for 40 frames.
numAsteroids = 0;
level = rand.nextInt(25)+1; // will be incremented to 1 when first level is set up
astRadius = 10; // values used to create the asteroids
minAstVel = 2;
maxAstVel = 8;
astNumHits = 3;
astNumSplit = 2;
money = 0;
fuel = 100;
endTime = 0;
startTime = 0;
framePeriod = 25;
addKeyListener(this); // tell it to listen for KeyEvents
dim = getSize();
img = createImage(dim.width, dim.height);
g = img.getGraphics();
thread = new Thread(this);
thread.start();
}
public void setUpNextLevel() { // start new level with one more asteroid
level++;
// create a new, inactive ship centered on the screen
// I like .35 for acceleration, .98 for velocityDecay, and
// .1 for rotationalSpeed. They give the controls a nice feel.
ship = new Ship(250, 250, 0, .35, .98, .1, 12);
numShots = 0; // no shots on the screen at beginning of level
paused = false;
shooting = false;
// create an array large enough to hold the biggest number
// of asteroids possible on this level (plus one because
// the split asteroids are created first, then the original
// one is deleted). The level number is equal to the
// number of asteroids at it's start.
asteroids = new Asteroid[level
* (int) Math.pow(astNumSplit, astNumHits - 1) + 1];
numAsteroids = level;
// create asteroids in random spots on the screen
for (int i = 0; i < numAsteroids; i++)
asteroids[i] = new Asteroid(Math.random() * dim.width,
Math.random() * dim.height, astRadius, minAstVel,
maxAstVel, astNumHits, astNumSplit);
}
public void paint(Graphics gfx) {
g.setColor(Color.black);
g.fillRect(0, 0, 500, 500);
for (int i = 0; i < numShots; i++)
// draw all the shots on the screen
shots[i].draw(g);
for (int i = 0; i < numAsteroids; i++)
asteroids[i].draw(g);
ship.draw(g); // draw the ship
g.setColor(Color.cyan); // Display level number in top left corner
g.drawString("Level " + level, 20, 20);
g.drawString("Money " + money, 80, 20);
g.drawString("Fuel " + fuel, 20, 50);
gfx.drawImage(img, 0, 0, this);
}
public void update(Graphics gfx) {
paint(gfx);
}
public void run() {
for (;;) {
startTime = System.currentTimeMillis();
// start next level when all asteroids are destroyed
if (numAsteroids <= 0)
setUpNextLevel();
if (!paused) {
ship.move(dim.width, dim.height); // move the ship
// move shots and remove dead shots
for (int i = 0; i < numShots; i++) {
shots[i].move(dim.width, dim.height);
// removes shot if it has gone for too long
// without hitting anything
if (shots[i].getLifeLeft() <= 0) {
// shifts all the next shots up one
// space in the array
deleteShot(i);
i--; // move the outer loop back one so
// the shot shifted up is not skipped
}
}
if(ship.accelerating && fuel>0){
fuel -= 1.5;
}
if(ship.accelerating && fuel == 0)
{
ship.accelerating = false;
}
// move asteroids and check for collisions
updateAsteroids();
if (shooting && ship.canShoot()) {
// add a shot on to the array
shots[numShots] = ship.shoot();
numShots++;
}
}
repaint();
try {
endTime = System.currentTimeMillis();
if (framePeriod - (endTime - startTime) > 0)
Thread.sleep(framePeriod - (endTime - startTime));
} catch (InterruptedException e) {
}
}
}
private void deleteShot(int index) {
// delete shot and move all shots after it up in the array
numShots--;
for (int i = index; i < numShots; i++)
shots[i] = shots[i + 1];
shots[numShots] = null;
}
private void deleteAsteroid(int index) {
// delete asteroid and shift ones after it up in the array
numAsteroids--;
for (int i = index; i < numAsteroids; i++)
asteroids[i] = asteroids[i + 1];
asteroids[numAsteroids] = null;
}
private void addAsteroid(Asteroid ast) {
// adds the asteroid passed in to the end of the array
asteroids[numAsteroids] = ast;
numAsteroids++;
}
private void updateAsteroids() {
for (int i = 0; i < numAsteroids; i++) {
// move each asteroid
asteroids[i].move(dim.width, dim.height);
// check for collisions with the ship, restart the
// level if the ship gets hit
if (asteroids[i].shipCollision(ship)) {
money+= Math.random()*1000;
deleteAsteroid(i);
//level--; // restart this level
//numAsteroids = 0;
return;
}
// check for collisions with any of the shots
for (int j = 0; j < numShots; j++) {
if (asteroids[i].shotCollision(shots[j])) {
// if the shot hit an asteroid, delete the shot
deleteShot(j);
// split the asteroid up if needed
if (asteroids[i].getHitsLeft() > 1) {
for (int k = 0; k < asteroids[i].getNumSplit(); k++)
addAsteroid(asteroids[i].createSplitAsteroid(
minAstVel, maxAstVel));
}
// delete the original asteroid
deleteAsteroid(i);
j = numShots; // break out of inner loop - it has
// already been hit, don't need to check
// for collision with other shots
i--; // don't skip asteroid shifted back into
// the deleted asteroid's position
}
}
}
}
public void keyPressed(KeyEvent e) {
if (e.getKeyCode() == KeyEvent.VK_ENTER) {
// These first two lines allow the asteroids to move
// while the player chooses when to enter the game.
// This happens when the player is starting a new life.
if (!ship.isActive() && !paused)
ship.setActive(true);
else {
paused = !paused; // enter is the pause button
if (paused) // grays out the ship if paused
ship.setActive(false);
else
ship.setActive(true);
}
} else if (paused || !ship.isActive()) // if the game is
return; // paused or ship is inactive, do not respond
// to the controls except for enter to unpause
else if (e.getKeyCode() == KeyEvent.VK_UP)
{if(fuel>0){
ship.setAccelerating(true);
//fuel -= 1.5;
}
else{
fuel = 0;
}
}
else if (e.getKeyCode() == KeyEvent.VK_LEFT)
{
ship.setTurningLeft(true);
}
else if (e.getKeyCode() == KeyEvent.VK_RIGHT)
ship.setTurningRight(true);
//else if (e.getKeyCode() == KeyEvent.VK_CONTROL)
//shooting = true; // Start shooting if ctrl is pushed
}
public void keyReleased(KeyEvent e) {
if (e.getKeyCode() == KeyEvent.VK_UP)
ship.setAccelerating(false);
else if (e.getKeyCode() == KeyEvent.VK_LEFT)
ship.setTurningLeft(false);
else if (e.getKeyCode() == KeyEvent.VK_RIGHT)
ship.setTurningRight(false);
//else if (e.getKeyCode() == KeyEvent.VK_CONTROL)
//shooting = false;
}
public void keyTyped(KeyEvent e) {
}
}

I believe that createImage() is going to return null until the component is actually on-screen, wihch i believe is after the thread has started.
Instead of this:
img = createImage(dim.width, dim.height);
g = img.getGraphics();
thread = new Thread(this);
thread.start();
try:
new Thread(new Runnable() {
public void run() {
do {
try {
Thread.sleep(25);
} catch(InterruptedException e) {
System.out.println("wait interrupted");
break;
}
} while(!isDisplayable());
// Now it should be safe to make these calls.
img= createImage(dim.width, dim.height);
g = img.getGraphics();
start();
}
}).start();