I am trying to write a program to play chess and I am having problems with the UI.
The display is really simple. A big JLabel that shows the current state of the chessboard occupies almost all of the window. Below it, in the same line, there are: a JLabel indicating what player must move, a JTextArea where he/she can write the move, a JButton to press when the player wants to submit the move.
There is a single event handled, the pressing of the JButton: when the button is pressed, the program excutes the move (not displayed because of SSCCE), creates a new image of the chessboard as it currently is, modifies the big JLabel to show the new image.
The reloading of the image is contained in the method reloadImage(). This method, among other things, calls the method setIcon() for the big JLabel: this in turn returns the following exception.
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at chess.ChessUI.reloadImage(ChessUI.java:145)
Anybody can help me?
SSCCE code snippet:
public class ChessUI extends JFrame {
// Swing fields
/**
*
*/
private static final long serialVersionUID = -2194112668235114615L;
// Swing fields
/** The greater {@link JPanel}. */
private JPanel contentPane;
/** The {@link ChessBoard} image. */
private JLabel boardImage;
/** The {@link ImageIcon} used in displaying the image. */
private Icon icon;
/** The text "Player moves". */
private JLabel playerIndicator;
/** The {@link JTextField} where the player can insert the move. */
private JTextField moveTextField;
/** The {@link JButton} for submitting a {@link ChessMove}. */
private JButton submitButton;
// Chess fields
// private ChessBoard board;
// private ChessImageCreator imgCreator;
private boolean whiteMoves = true;
public String path = "D:\\ChessProgram\\Board.jpg";
public String path2 = "D:\\ChessProgram\\test.png";
// =========================================================
// TODO | Constructors
/**
* Create the frame.
*/
public ChessUI() {
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setBounds(100, 100, resolutionWidth, resolutionHeight);
contentPane = new JPanel();
// contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
contentPane.setBorder(new EmptyBorder(margin, margin, margin, margin));
setContentPane(contentPane);
contentPane.setLayout(null);
// Text
this.playerIndicator = new JLabel(" White moves. Insert move:");
playerIndicator.setBounds(0, imageResolution + margin, textWidth, buttonHeight);
contentPane.add(playerIndicator);
// Move field
moveTextField = new JTextField();
moveTextField.setBounds(textWidth + margin, imageResolution + margin, moveWidth, buttonHeight);
contentPane.add(moveTextField);
moveTextField.setColumns(10);
// Submit button
submitButton = new JButton("Submit");
submitButton.addMouseListener(new MouseAdapter() {
@Override
public void mouseClicked(MouseEvent arg0) { }
} );
submitButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent arg0) {
// Acquire the input move
// ChessMove move = new ChessMove(moveTextField.getText(), board);
// If the move is acceptable...
// if( move.isValid(board.errorManager()) )
if( true ) // the condition has been changed to ensure the minimallity of the code example
{
// ...executes it...
// board.move(move);
reloadImage();
// ...changes the player...
whiteMoves = ! whiteMoves;
// ...and corrects the text specifying who can move.
playerIndicator.setText(" " + (whiteMoves ? "White" : "Black") + " moves. Insert move: ");
}
// If the move is invalid, the ErrorManager will act inside the call of the method .isValid()
}
} );
submitButton.setBounds(resolutionWidth - buttonWidth - 2*margin, imageResolution + margin, buttonWidth, buttonHeight);
contentPane.add(submitButton);
// Chess management
// this.board = new ChessBoard();
// this.imgCreator = new ChessImageCreator(board);
// ChessBoard image
// imgCreator.createImage(imageResolution/StdDraw.scale(), path);
icon = new ImageIcon(path);
JLabel lblImage = new JLabel(icon);
// lblImage.setBackground(Color.PINK);
lblImage.setBounds(0, 0, imageResolution, imageResolution);
contentPane.add(lblImage);
}
// =========================================================
// TODO | Graphic methods
public void reloadImage() {
// Recreate the image
// imgCreator.createImage(imageResolution/StdDraw.scale(), path);
// Reload the image
icon = new ImageIcon(path2); // Chosen path2 because of SSCCE
if( icon == null ) System.out.println("ICON IS NULL");
boardImage.setIcon(icon); // THIS LINE CAUSES EXCEPTION
}
// =========================================================
// TODO | Graphic setting
/** The number of pixels between the image of the {@link ChessBoard} and the {@link JFrame},
* and the number of pixels between the image and the interactive {@link JButton}. */
public int margin = defaultMargin;
/** The width and height of the image of the {@link ChessBoard}. */
public int imageResolution = defaultImageWidth;
/** The width of the window in pixel. */
public int resolutionWidth = imageResolution + 2*margin;
/** The height of the interactive {@link JButton} in pixel. */
public int buttonHeight = defaultButtonHeight;
/** The width of the interactive {@link JButton} in pixel. */
public int buttonWidth = defaultButtonWidth;
/** The width of the text "Player moves" in pixel. */
public int textWidth = defaultTextWidth;
/** The width of the field where the user can insert his/her {@link Move}. */
public int moveWidth = resolutionWidth-4*margin-textWidth-buttonWidth;
/** The height of the window in pixel. */
public int resolutionHeight = imageResolution + 2*margin + 3*buttonHeight;
/** The width of the window in pixel. */
// public int resolutionWidth = defaultFrameWidth;
/** The width and height of the image of the {@link ChessBoard}. */
// public int imageResolution = resolutionWidth - 2*margin;
// public static final int defaultFrameWidth = 612;
public static final int defaultImageWidth = 800;
public static final int defaultFrameHeight = 800;
public static final int defaultMargin = 10;
public static final int defaultButtonHeight = 25;
public static final int defaultButtonWidth = 100;
public static final int defaultTextWidth = 160;
// =========================================================
// TODO | Main
/**
* Launch the application.
*/
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
ChessUI frame = new ChessUI();
frame.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
}
