private static final long serialVersionUID = 1234567L

public abstract class GameCore extends JFrame{

  ////////////////////////
  //       Variables      //
  ////////////////////////

  public static final float FONT_SIZE = 14.0f;
  public static final int GAME_WIDTH = 800;
  public static final int GAME_HEIGHT = 544;

  private boolean isRunning;

  protected GameCanvas gameCanvas;

  private JFileChooser fileChooser = new JFileChooser();

  ////////////////////////
  //        Methods      //
  ////////////////////////

  //Signals the game loop that it's time to quit
  public void stop() {
    isRunning = false;
  }

  //Calls init() and gameLoop()
  public void run() {
    try{
      init();
      gameLoop();
    }
    finally{
      //screen.restoreScreen();
      lazilyExit();
    }
  }


  
  //Exits the VM from a daemon thread. The daemon thread waits
  //2 seconds then calls System.exit(0). Since the VM should
  //exit when only daemon threads are running, this makes sure
  //System.exit(0) is only called if neccesary. It's neccesary
  //if the Java Sound system is running.
  public void lazilyExit() {
    Thread thread = new Thread() {
      public void run() {
        // first, wait for the VM exit on its own.
        try {
          Thread.sleep(2000);
        }
        catch (InterruptedException ex) { }
          // system is still running, so force an exit
          System.exit(0);
        }
      };
    thread.setDaemon(true);
    thread.start();
  }

  //Sets full screen mode and initiates and objects.
  public void init() {

    //create a frame to contain our game
    setTitle("Age of the Dead - by Mathew Brenaman");

    //Set main game frame
    setBackground(Color.black);
    setForeground(Color.white);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setIconImage(loadImage("Icon.gif"));

    gameCanvas = new GameCanvas();

    gameCanvas.setBackground(Color.black);
    gameCanvas.setForeground(Color.white);
    gameCanvas.setPreferredSize( new Dimension(GAME_WIDTH,GAME_HEIGHT));
    gameCanvas.setDoubleBuffered(true);
    gameCanvas.setFocusable(true);

    //Set font
    try{
      gameCanvas.setFont(Font.createFont(Font.TRUETYPE_FONT,getClass().getResourceAsStream("Calisto.TTF") ).deriveFont(FONT_SIZE)  );
    }catch(Exception e){ 
      System.out.print("\nError in loading Calisto.ttf, unable to start game...\n");
      return; 
    }

    //Set the preffered size of the content pane and add the canvas to it            
    Container c = getContentPane();
    c.setLayout(new FlowLayout());
    c.add(gameCanvas);

    gameCanvas.requestFocus();    // the JPanel now has focus, so receives key events

    pack();
    setVisible(true);
    gameCanvas.setVisible(true);
    show();
               

    setExtendedState(Frame.MAXIMIZED_BOTH);


    isRunning = true;

  }


  //Load image using ImageIO
  public BufferedImage loadImage(String fileName) {
    try{
      return ImageIO.read( getClass().getResourceAsStream(fileName) );
    }
    catch(IOException e){}
    return null;
  }

  //Method uses and displays a JFileChooser dialog box for saving/loading,
  //and returns the file choosen, do not provide a dot for the extensions
  public File showFileChooser(String dialogTitle,String approveButtonText,
                              String approveButtonToolTip, char approveButtonMnemonic,ExtensionFilter extensionFilter,boolean saveFile){

    fileChooser.setDialogTitle(dialogTitle);
    fileChooser.setApproveButtonText(approveButtonText);
    fileChooser.setApproveButtonToolTipText(approveButtonToolTip);    
    fileChooser.setApproveButtonMnemonic(approveButtonMnemonic);
    fileChooser.addChoosableFileFilter(extensionFilter);
    fileChooser.setFileFilter(extensionFilter);
    fileChooser.rescanCurrentDirectory();
    
    int result;
    if(saveFile){
      result = fileChooser.showSaveDialog(GameCore.this);
      File fileResult = (result == fileChooser.APPROVE_OPTION) ? fileChooser.getSelectedFile() : null;
      if(fileResult!=null){
        if(!fileResult.getName().toLowerCase().endsWith(extensionFilter.getExtension()))
          fileResult = new File(fileResult.getAbsolutePath() +"."+extensionFilter.getExtension());
      }
      return fileResult;
    }    
    else{
      result = fileChooser.showOpenDialog(GameCore.this);
      return (result == fileChooser.APPROVE_OPTION) ? fileChooser.getSelectedFile() : null;
    }

  }

  //Runs through the game loop until stop() is called.
  public void gameLoop() {

    long startTime = System.currentTimeMillis();
    long currTime = startTime;
    TimeSmoothie timeSmoothie = new TimeSmoothie();

    while(isRunning){
      long elapsedTime =
        System.currentTimeMillis() - currTime;
      currTime += elapsedTime;            
        
      //update
      update(timeSmoothie.getTime(elapsedTime));

      gameCanvas.repaint();

      // Sync the display on some systems.
      // (on Linux, this fixes event queue problems)
      Toolkit.getDefaultToolkit().sync();

    }
  }

  //Updates the state of the game/animation based on the
  //amount of elapsed time that has passed.
  public void update(long elapsedTime) {
      // do nothing
  }

  //Draws to the screen. Subclasses must override this
  //method.
  public abstract void draw(Graphics g);



  public void paint(Graphics g) {
    g.setColor(Color.BLACK);    
    g.fillRect(0,0,getWidth(),getHeight());    
    gameCanvas.repaint(); 
  }


  public class GameCanvas extends JPanel {

    protected void paintComponent(Graphics g) {
      draw(g);
    }
  
  }

}//End of GameCore class