1. on radiobuttons:

JRadioButton a= new JRadioButton("A");
JRadioButton b= new JRadioButton("B");
ButtonGroup bg = new ButtonGroup();
bg.add(a); bg.add(b);
JPanel mode = new JPanel(new GridLayout(1, 1));
mode.add(bg);

ERROR:
Incompatible type for method. Can't convert javax.swing.ButtonGroup to java.awt.Component.

eh?

2. also, how do i use the isSelected method so that radiobutton "A" is selected on load?

3. finally, x.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); in void main, but it doesn't work, something like EXIT_ON_CLOSE not declared...