I am not too good at graphical user interfaces so I am looking for some advice.
The think is I have several Panels containing a GridPanel, to be more specific I have 4 of them.
I need to put all of them in a unique Panel but I cannot find any suitable layout. I have tried plenty of them but it does not display correctly. I need them to fill all the width and the height.
I am able to display 3 of them by using BorderLayout (west, center and east) but no way to do it with four.
Normally the DockPanel is used to display Widgets with header and footer (with some more panels in east or west).
The is no restriction as to what can added to header (eg you can add a grid with 3 rows to the header, etc..)
As far as your problem is concerned,
You can either use a vertical panel with width set to 100%
or you can use a Grid with width and height set to 100%
(Be warned that though gwt allows setting height to tables, height is not a standard attribute for TABLE tag in HTML. So... You might have to calculate it based on screen height, etc..)