I was going through my simple game application streamlining everything from 700 lines down to 177 getting rid of repetition. When I try running my application I get a Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException thrown at me. I know what it means (from reading this) and I know it has something to do with how I'm doing the actionListener but i don't know exactly how.
I followed all the tutorials I came across dealing with Arrays and JButtons but there must be something little going wrong. private JButton[][] blocks = new JButton[rows][cols] is being declared correctly so it's not that and I didn't change how I did blocks[i][j].addActionListener(this) from a previous version of my code except for the fact that I changed block1, block2... etc with block[i][j].
Here is what was thrown at me:
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at blox.Blox.game(Blox.java:105)
at blox.Blox.access$000(Blox.java:25)
at blox.Blox$1.run(Blox.java:173)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:251)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:727)
at java.awt.EventQueue.access$200(EventQueue.java:103)
at java.awt.EventQueue$3.run(EventQueue.java:688)
at java.awt.EventQueue$3.run(EventQueue.java:686)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:697)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)
And here is my code:
public class Blox implements ActionListener {
private final String gameVersion = "Blox - v1.0.2";
private final int rows = 7;
private final int cols = 7;
// Board Inits
private ImageIcon purpleBlock = new ImageIcon();
private ImageIcon redBlock = new ImageIcon();
private ImageIcon blueBlock = new ImageIcon();
private ImageIcon greenBlock = new ImageIcon();
private ImageIcon closeImage = new ImageIcon();
private JButton[][] block = new JButton[rows][cols];
private JPanel boardBg = new JPanel();
// Error console init
private JLabel errorMessage = new JLabel();
private JPanel errorBg = new JPanel();
private JButton closeError = new JButton();
// Score/UI Inits
private JButton resetBoard = new JButton("Reset Board");
/**
* 700 x 480 Frame Size
* Sets Up and displays initial scene.
*
*/
private void game() {
// Initialize mainFrame
JFrame mainFrame = new JFrame(gameVersion);
Dimension minSize = new Dimension(700,480);
mainFrame.setMinimumSize(minSize);
mainFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
mainFrame.setLayout(null);
mainFrame.setResizable(false);
try {
mainFrame.setContentPane(new JLabel(new ImageIcon(
ImageIO.read(new File("bggrad.jpg")))));
} catch (IOException e) {
e.printStackTrace();
}
// Setup block Images
try {
purpleBlock.setImage(ImageIO.read(new File("purpleBlock.png")));
redBlock.setImage(ImageIO.read(new File("redBlock.png")));
blueBlock.setImage(ImageIO.read(new File("blueBlock.png")));
greenBlock.setImage(ImageIO.read(new File("greenBlock.png")));
closeImage.setImage(ImageIO.read(new File("close.jpg")));
} catch (IOException e) {
e.printStackTrace();
}
// Sets up error message panel
// Only displayed if error occurs on ActionListener
errorMessage.setText("");
errorMessage.setForeground(Color.black);
Font newLabelFont = new Font(errorMessage.getFont().getName(),
Font.BOLD,errorMessage.getFont().getSize());
errorMessage.setFont(newLabelFont);
closeError.setIcon(closeImage);
closeError.setBounds(0,0,24,24);
errorBg.setBounds(0,430,700,30);
errorBg.setBackground(Color.lightGray);
errorBg.add(closeError);
errorBg.add(errorMessage);
errorBg.setVisible(false);
// Sets up Score/UI Portions of Screen
resetBoard.setBounds(60,363,175,25);
resetBoard.setVisible(true);
resetBoard.addActionListener(this);
// Set Up Board
boardBg.setLayout(new GridLayout(rows,cols));
boardBg.setBounds(300,50,350,350);
for(int i=0; i<rows; i++) {
for(int j=0; i<cols; j++) {
block[i][j].setIcon(randomizer());
block[i][j].addActionListener(this);
boardBg.add(block[i][j]);
}
}
mainFrame.getContentPane().add(boardBg);
mainFrame.getContentPane().add(errorBg);
mainFrame.getContentPane().add(resetBoard);
//mainFrame.pack();
mainFrame.setVisible(true);
}
/**
* Checks onClick event for which JButton was clicked
* and changes JButton.setIcon() accordingly.
*
* @param none
* @return none
* @see java.awt.event.*
* @see JButton
* @see setIcon()
* @see getIcon()
*
*/
public void actionPerformed(ActionEvent e) {
if(e.getSource()==resetBoard) {
System.out.println("Resetting");
gameReset();
}
if(e.getSource()==errorBg || e.getSource()==errorMessage) {
errorBg.setVisible(false);
}
}
public void gameReset() {
for(int i=0; i<rows; i++) {
for(int j=0; i<cols; j++) {
block[i][j].setIcon(randomizer());
}
}
}
public ImageIcon randomizer() {
Random r = new Random();
int rNum = r.nextInt(4);
if(rNum==0) {
return purpleBlock;
} else if(rNum==1) {
return redBlock;
} else if(rNum==2) {
return greenBlock;
} else {
return blueBlock;
}
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
new Blox().game();
}
});
}
}
