With BorderLayout you can only put one component in any one region. If you want to add more than one component to a region you have to add the components to a container component such as JPanel and add the container component to the region.

So, if you want to add 3 buttons to the SOUTH region then you need to add those 3 buttons to a JPanel and add the JPanel to the SOUTH region. There are a number of layout managers you could use in the JPanel to layout the buttons but FlowLayout with a center alignment and small inter component spacing is probably the one you want. ie

Code:
new FlowLayout(FlowLayout.CENTER);