java ButtonGroup及JRadioButton用法

package com.xinhua.testswing;


import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;


import javax.swing.ButtonGroup;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JRadioButton;


public class TestJRadioButton extends JFrame {
JRadioButton jrb1;
JRadioButton jrb2;
JRadioButton jrb3;
JRadioButton jrb4;


public TestJRadioButton() {
jrb1 = new JRadioButton("china");
jrb2 = new JRadioButton("usa");
jrb3 = new JRadioButton("Egl");
jrb4 = new JRadioButton("fra");

ButtonGroup bg = new ButtonGroup();
bg.add(jrb1);
bg.add(jrb2);
bg.add(jrb3);
bg.add(jrb4);

// jp.add(bg);
JPanel jp = new JPanel();
jp.add(jrb1);
jp.add(jrb2);
jp.add(jrb3);
jp.add(jrb4);
//注意jrb1,jrb2,jrb3,jrb4被添加两次，一次是加入到ButtonGroup中，一次是JPanel中，但ButtonGroup不需要被添加
getContentPane().add(jp);

jrb1.addItemListener(new ItemListener() {

@Override
public void itemStateChanged(ItemEvent e) {


if (jrb1.isSelected()) {
System.out.println(jrb1.getText());
}

}
});

jrb2.addItemListener(new ItemListener() {

@Override
public void itemStateChanged(ItemEvent e) {


if (jrb2.isSelected()) {
System.out.println(jrb2.getText());
}

}
});

jrb3.addItemListener(new ItemListener() {

@Override
public void itemStateChanged(ItemEvent e) {
if (jrb3.isSelected()) {
System.out.println(jrb3.getText());
}
}
});

jrb4.addItemListener(new ItemListener() {

@Override
public void itemStateChanged(ItemEvent e) {


if (jrb4.isSelected()) {
System.out.println(jrb4.getText());
}
}
});

setSize(300, 200);
setVisible(true);

}



public static void main(String[] args) {
new TestJRadioButton();
}


}