GridBagLayout: how to fill all empty spaces

Question

I've have a JFrame contains some JPanels using a gridBagLayout (3 rows, one column). That's my code:

Container main_container = getContentPane();
GridBagLayout layout = new GridBagLayout();
main_container.setLayout(layout);
GridBagConstraints c = new GridBagConstraints();

StatoMagazzini jpanel_stato_magazzini = new StatoMagazzini();
c.gridx = 1;
c.gridy = 2;
c.fill = GridBagConstraints.BOTH;
layout.setConstraints(jpanel_stato_magazzini, c);

AcquistoLotto jpanel_acquisto = new AcquistoLotto(i, jpanel_stato_magazzini);
c.gridx = 1;
c.gridy=1;
c.fill = GridBagConstraints.HORIZONTAL;
c.anchor = GridBagConstraints.FIRST_LINE_START;
layout.setConstraints(jpanel_acquisto, c);

ButtonPanel jpanel_button_panel = new ButtonPanel(i);
c.gridx=1;
c.gridy=3;
c.anchor = GridBagConstraints.CENTER;
layout.setConstraints(jpanel_button_panel, c);

main_container.add(jpanel_acquisto);
main_container.add(jpanel_stato_magazzini);
main_container.add(jpanel_button_panel);
pack();

and that's the result (a ugly result): https://docs.google.com/file/d/0Bxi2arJ2Dv9xbEo0Smd5QUN4UGc/edit?usp=sharing

i would eliminate that empty spaces on top and extend the second component (that is a scrollable JTable). How i should modify code?

Answer 1

When a GridBagLayout has more space than it needs, it distributes that extra space using the weightx and weighty properties of each cell. If no cells have a non-zero weight property, the extra space is not allocated to any cell, and instead all cells are centered, and sized to their preferred width/height.

If you do c.weighty = 1 for the constraints used by the component containing the JTable, that component will be allocated all extra vertical space. You may also want to do c.weightx = 1 so the table will fill all horizontal space.