I have code like that:
JPanel myPanel = new JPanel();
myPanel.setLayout(new BoxLayout(myPanel, BoxLayout.Y_AXIS));
JButton button = new JButton(
If you're definitely intending to use BoxLayout to layout your panel, then you should have a look at the How to Use BoxLayout Sun Learning Trail, specifically the Using Invisible Components as Filler section. In short, with BoxLayout you can create special invisible components that act as spacers between your other components:
container.add(firstComponent);
container.add(Box.createRigidArea(new Dimension(5,0)));
container.add(secondComponent);