關於ButtonGroup和JRadioButton的應用

import java.awt.*;

import javax.swing.*;

public class JRadioButtonTest extends ButtonGroup{
	
	JRadioButtonTest(){
		JFrame f = new JFrame("單選框示例");//建立一個JFrame的物件
		Container contenPane = f.getContentPane();//建立一個內容面板容器
		contenPane.setLayout(new FlowLayout());//設定該容器的佈局
		JPanel pl = new JPanel();//建立一個面板物件pl
		pl.setLayout(new GridLayout(1 ,3));//設定該面板的佈局管理器格式
		pl.setBorder(BorderFactory.createTitledBorder("選擇你喜歡的城市"));
		//定義3個JRadioButton單選按鈕
		JRadioButton r1 = new JRadioButton("北京");
		JRadioButton r2 = new JRadioButton("上海");
		JRadioButton r3 = new JRadioButton("青島");
		ButtonGroup bg = new ButtonGroup();//建立一個ButtonGroup物件
		bg.add(r1);
		bg.add(r2);
		bg.add(r3);
		pl.add(r1);
		pl.add(r2);
		pl.add(r3);
		contenPane.add(pl);
		f.pack();
		f.setVisible(true);
	}
	public static void main(String[] args){
		JRadioButtonTest jbt = new JRadioButtonTest();
	}
}