A good answer might be:

One.

Radio Buttons

Car radios and some table radios have buttons for selecting a radio station. Only one station is selected at a time. When one button is pushed in the previous selection pops out. The Swing class JRadioButton works the same way. Radio buttons must be members of a ButtonGroup. Only one button of a button group is selected at a time.

A constructor for JRadioButton is as follows. There are other constructors that may be useful (see the Java documentation).

JRadioButton( String text, boolean selected )

The text is the words that next to the button. If selected is true then this button starts out selected. Only one button of a button group may start out as selected. JRadioButton is a child class of JAbstractButton. Radio buttons and push buttons have many methods in common.

QUESTION 2:

(Thought Question: ) Does clicking on a radio button generate an action event?