How to make a JPanel expand to max width in another JPanel

Question

I feel I need to rephrase the question a bit.

Updated question below.

I have a JPanel that contains:

myjpanel.setLayout(new BoxLayout(selectors, BoxLayout.PAGE_AXIS));

It contains the following three panels:

JPanel with fixed size 'x' and 'y'

JPanel with no fixed size

JPanel with no fixed size and small height

The second JPanel contains a JTable so it expands to fill the full height and pushes the bottom panel all the way down, as expected.

Like this:

t
t
m
m
m
m
m
b

t = top panel, m = middle panel, b = bottom panel.

That works. But the bottom panel does not feel like filling the entire width of the parent which is a problem.

ttt
mmm
 b 

I would like either this, where the panel fills the entire width:

ttt
mmm
bbb

or this, where the bottom panel is left centered:

ttt
mmm
b

---

Old question below:

I have a JPanel that contains:

.setLayout(new BoxLayout(selectors, BoxLayout.PAGE_AXIS));

Within it, there are three more JPanels. The first two are of fixed size and the middle one isn't.

I want my bottom panel to take only the height it needs, but uses all the available width of the outer JPanel.

I have tried using glue but to no avail, and I would rather not set preferred and min/max sizes. Is there a way to tell the component to "Fill the entire parents width" using just the layout manager and framework. I would rather not start to do hacks like setting sizes and overriding methods.

Note: I can't put any glue or filler in the inner panel, only the outer panel and its layout manager can be modified.

Attempt 1:

Using myPanel.setLayout(new GridLayout(3, 1)); did not produce the expected results. It made a grid like this:

XX
 X

But I expected:

X
X
X

Attempt 2:

Using myPanel.setLayout(new GridLayout(0,1)); did not produce the expected results. It made a grid like this:

x
x
x

But all panels were of the same size, ignoring the restraints.

Answer 1

The easiest way would be to use another layout manager such as GridLayout that automatically sizes components to fill the parent container.

myPanel.setLayout(new GridLayout(0, 1));