What is the correct way to set size of elements of GUI?

I am using swing to create my GUI. J have a JFrame containing one main JPanel which, in its turn contain several JPanels which, in their turn, contain buttons.

I would like to set certain sizes to mu buttons and JPanels. How does it work? Should I set sizes of my buttons and then the size of the JPanel and the JFrame will be set according to the buttons sizes? Or it works in the opposite direction? I set size for the JPanel and the size of the buttons will be set automatically?

ADDED:

I used fieldPanel.setPrefer开发者_如何学编程redSize(new Dimension(100,100)); and it had no effect on the appearance of the window. Can it be because this panel is in the "middle of the hierarchy" it contains some buttons and it is contained by other JPanels?

It depends on the layout manager that you use. Some, like GridLayout does not pay attention to the size that you set but rather apply the rules of the layout manager itself.

Others, like GridBagLayout, you have better control over the size of the components.