Java's Swing seems to be changing the layout from Card Layout

Question

I am having some pretty strange symptoms with JPanels and CardLayout. Essentially, I have cards which act as "pages" since I can only hold 12 cells on the grid, and I display each page as a card, and clicking -> and <- buttons change pages accordingly (or that's the idea). Because this data is representing a changing model, every five seconds I was going to have new cards be added displaying updated information, and simply remove the old pages.

Essentially, I construct the initial pages when the program starts:

public OrderSimPanel() {
    super( new CardLayout() );

    // Create the map
    frames = new TreeMap<Integer, String>();

    // Update and draw
    refreshRelevantOrders();
    drawPanel();

    // Set a timer for future updating
    java.util.Timer timer = new java.util.Timer();
    timer.schedule(new UpdateTask(), 5000);

    System.out.println("Constructor DOES get called");
    System.out.println("Panel type is " + this.getLayout().getClass().getName() );
}

Where refershReleventOrders() just updates an List, and drawPanel() is something like this:

private void drawPanel() {
    System.out.println("Panel type is " + this.getLayout().getClass().getName() );

    // Set all old frames to depricated
    for( Integer k : frames.keySet() ) {
         String o = frames.get( k );
         frames.remove(k);
         k = -k;
         frames.put(k, o);
    }

    // Frame to add to
    JPanel frame = new JPanel( new GridLayout(3,4) );
    int f = 0;

    // Create new cells in groups of 12
    for( int i = 0; i < orders.size(); i++ ) {
        // Pagination powers activate!
        int c = i % 12;
        f = i / 12;

        // Create a new panel if we've run out of room on this one
        if ( c == 0 && i > 0 ) {
            // Add old frame
            String id = new Double( Math.random() ).toString();
            frames.put(f, id);
            add( frame, id );

            // Create new one
            frame = new JPanel( new GridLayout(3,4) );
        }

        // Add the order cell to the panel
        frame.add(new OrderCellPanel( orders.get(i) ));

        i++;
    }

    // Add last frame
    String id = new Double( Math.random() ).toString();
    frames.put(f, id);
    add( frame, id );

    // Set active frame to 0'th frame
    ((CardLayout)(this.getLayout())).show(this, frames.get(0));

    // Erase other frames and from map
    for( Integer k : frames.keySet() ) {
        if( k < 0 ) {
            this.remove(0);
            frames.remove(k);
        }
    }
}

The timer task created in the constructor calls refreshRelevantOrders() an drawPanel(). The initial print output looks like this:

Panel type is java.awt.CardLayout
Constructor DOES get called
Panel type is java.awt.CardLayout

But when the timer executes, this is displayed:

Panel type is javax.swing.GroupLayout

And of course, the casting code in drawPanel() fails. Thanks for any ideas!

Answer 1

Override setLayout() method, and print the old / new layout class names there (before or after calling the super implementation). This way you will see which part of your code sets GroupLayout on the panel.