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Make children of JLayeredPane fill available space of container

I have two JPanel instances in a JLayeredPane, on different z-orders. I want both of my child JPanels to always fill the space of the LayeredPane.
The idea is for me to toggle the display of a 2nd panel over top of the first to display a modal-like dialog. Yes, I could just use a JDialog, but I thought it would be fun to try and create some transparancy overtop of the covered JPanel for a nice effect.
I find that using a layout manager on the JLayeredPane, like BorderLayout, and trying to set both children to CENTER conflicts since both panels can't be in the Center.
Is there a trick that I'm not seeing?

The idea is for me to toggle the display of a 2nd panel over top of the first
The easiest way to do this is to use a Glass Pane.
Check out the Disabled Glass Pane for an example of this approach.

There are two ways to create some "Glass Panel like" overlay for JPanels with JLayeredPane:
Add a ComponentListener to the JLayeredPane and update the sizes of all child components whenever the size of the JLayeredPane changes
Create a simple FillLayout, which expands the size of its child Components to the size of the Layout Container (In our case the JLayeredPane). You need to keep a list of children Components. During layoutContainer you copy the dimensions of the Container to these child Components. I wrote this and its really simple, but unfortunately I can't post it, since it's corporate. But if anyone is interested just ask in the comments. The implementation basically consists of one-liners.
For both solutions you need to make sure, that the panels on top are transparent, by setting setOpaque to false. This ensures that underlying panels render their content.

Auto scaling components with Java JFrame [duplicate]

Not sure if what I need is possible.
I have a container (JPanel) that contains some internal elements.
I was wondering if it is possible to force internal elements to fit into the container's size.
I need them to be fully visible i.e., resize to fit inside the Panel's size and not cut some parts of the internal elements.
Scrolling is not an option.
Is this possible by using a Layout or something?
EDIT: Important clarification:
The thing is that I do not have access to the internal elements neither to their properties so I would say that a Layoutmanager capable of resizing child elements to fit to its size is needed. I tested BorderLayout and GridBagLayout but the result is always the same, the internal elements are cut out.

It's for exactly that reason that LayoutManagers exist. All the LayoutManagers work for simple containers directly, excluding GridBagLayout which is to able to handle most complete GUIs directly.
For most complete GUI's you have some choices as follows:
Look for a 3rd party layout such as MigLayout or here
Use GridBagLayout
Very easy way is use nested layout, where there is more than one JPanel and each has child JPanels with the same or different LayoutManager
Or custom layout, should be hard..., but same as using GridBagLayout

You could set the JPanel layout to border layout, then add the single child to the center. If there are multiple children, this approach becomes less useful since components added to the the NORTH, SOUTH, EAST, and WEST will remain statically sized while the centre resizes to fill the remainder.
In short, this isn't an ideal solution. All layouting in Swing is made all the more complex by the fact that different components behave in different ways, so you really need to provide further details of the child components you wish to add to your panel, and any behaviour that has been overridden on those components.
The best way is to try a couple of simple examples to see what mileage you get and whether subtle redesign of your child component nesting could help.

you can use a layout, like GridBagLayout, or BorderLayout depending on the situation. With proper weights it is possible.

this sounds to me like you should just peek an appropriate layout manager and use it. For example, look at BorderLayout - put your component in the CENTER and it will occupy all the area. Its up to each concrete layout manager to decide what will be the size of the components.
Mark

I was using a JInternalFrame inside JDesktopPane. I wanted the internal_frame to auto resize as desktop pane is resized, so I had to implement the AncestorResized event for the internal frame where I placed the following code:
this.setPreferredSize(this.getParent().getPreferredSize());
this.pack();

Working with GUI's in java

I really need some help i've tried many scenarios of code and none seem to deliver the outcome.
I would like to produce a GUI where the Question is on one line and centered and the possible answers are on the next line centered too. I've produced this code - my thinking was make a Box Layout and add two flow layouts inside the box layout one for the question and one for the possible answers

This behavior is correct as you are using FlowLayout.
The FlowLayout class puts components in a row, sized at their
preferred size. If the horizontal space in the container is too small
to put all the components in one row, the FlowLayout class uses
multiple rows.If the container is wider than necessary for a row of
components, the row is, by default, centered horizontally within the
container.
Use any other layout such as SpringLayout or GridBagLayout.

A Flexible Layout manager that will change the layout according to resize

In my JPanel, I have 6 buttons laid out in a row (using FlowLayout as of now). The default size of the panel is enough to accommodate these buttons in one row. But, when the frame is resized it gets stuck at the size that is the sum of the minimum sizes of each button.
I need a layout manager that simply puts the buttons in a new row on re-sizing of the panel.
I'm pretty new to Java Swing so I apologize in advance if this is a trivial question.

MigLayout is by far the best layout manager I've ever used. Things that used to require nested containers and lots of hard to understand code can be done in a single container with simple to understand (and maintain) string constraints.

The flow layout is capable of your desired behavior (moving components into new row if they cannot fit). Check out the swing tutorial (run FlowLayoutDemo). You'll have to show us your source code to find out, whether there is some other constrain which prevents it.

FlowLayout does actually paint components on a new row, but the problem is that the preferred size of the panel doesn't change so in many cases you can't see the components (unless you happen to add the panel to the CENTER of a BorderLayout).
One solution is to use the Wrap Layout, which extends FlowLayout to recalculate the preferred size of the panel so that you see the buttons on a new row.

Java - Is it possible to put a JLayeredPane inside JScrollPane?

when I try putting my JLayeredPane inside a JScrollPane I get a blank window (with white background) instead of the content I am trying to render (it could be an image, a button, a canvas). Does anyone know of a problem with layout managers that might cause it? Is it possible?
EDIT:
thanks to camickr help, I can now put a JLayeredPane inside a JScrollPane, though now I am facing a different problem:
I am using a very large image and I am trying to put it inside my JLayeredPane that's inside the JScrollPane. From some reason when I use this large image (I am not receiving a heap overflow exception) I get this blank (white screen). Has anyone experienced something like this?

Well this is pretty much a guess because you haven't provided much information, but it sounds to me like the JLayeredPane's preferred size is (0,0), and the "white" you're seeing is the background of the JScrollPane's JViewport child. Try setting a preferred size on the JLayeredPane as a start.

Read the Swing tutorial on How to Use Layered Panes for a working example.
Change the following line:
// add(layeredPane);
add(new JScrollPane(layeredPane));