How do I use the Button Group Swing control in Java?

To select a radio button programmatically, try these:

private final ButtonGroup buttonGroup = new ButtonGroup();

JRadioButton btn01 = new JRadioButton("btn 1");
buttonGroup.add(btn01);
JRadioButton btn02 = new JRadioButton("btn 2");
buttonGroup.add(btn02);
JRadioButton btn03 = new JRadioButton("btn 3");
buttonGroup.add(btn03);
// gets the selected radio button
if(buttonGroup.getSelection().equals(btn01.getModel())) {
 // code
}

// similarly for the other radio buttons as well.

How to Use Buttons, Check Boxes, and Radio Buttons

ButtonGroup group = new ButtonGroup();
group.add(new JRadioButton("one"));
group.add(new JRadioButton("two"));
//TO FIND SELECTED
//use a loop on group.getElements();
//and check isSelected() and add them
//to some sort of data structure

1. Drag a ButtonGroup from the palette and drop it on your GUI. It will show up under Other Components in the Inspector panel.
2. Right-click on it and Change variable name to something meaningful.
3. Now select a radio button in your GUI.
4. In the Properties panel look for the buttonGroup property.
5. Click the combo box next to it and select your button group.

I highly recommend reading this excellent tutorial. Here's an excerpt of code from the article that satisfies your question on how to create and add buttons to a ButtonGroup:

JRadioButton birdButton = new JRadioButton(birdString);
birdButton.setSelected(true);

JRadioButton catButton = new JRadioButton(catString);

   //Group the radio buttons.
ButtonGroup group = new ButtonGroup();
group.add(birdButton);
group.add(catButton);

As far as getting which item is selected, you basically need to iterate through the items in the group calling isSelected.