// TestRadioButton.java
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class TestRadioButton extends JFrame implements ItemListener
{
	//创建三个单选按钮
	private JRadioButton rb1 = new JRadioButton("居左对齐",false);
	private JRadioButton rb2 = new JRadioButton("居中对齐",false);
	private JRadioButton rb3 = new JRadioButton("居右对齐",false);
	//创建一个按钮组,用于实现单选按钮之间的互斥
	private ButtonGroup group = new ButtonGroup();
	private JTextField jtf = new JTextField("Hello");
	//构造方法
	public TestRadioButton()
	{	
		setTitle("单选按钮");
		JPanel p1 = new JPanel();
		p1.setLayout(new FlowLayout(FlowLayout.CENTER,20,10));
		//将三个单选按钮添加到面板p1上
		p1.add(rb1);
		p1.add(rb2);
		p1.add(rb3);
		//将三个单选按钮添加到按钮组group中,实现三个按钮之间的互斥
		group.add(rb1);
		group.add(rb2);
		group.add(rb3);
		//将面板p1和文本框jtf分别添加到内容窗格的相应区域
		getContentPane().add(p1,BorderLayout.CENTER);
		getContentPane().add(jtf,BorderLayout.NORTH);
		//为三个单选按钮注册ItemEvent事件的监听器
		rb1.addItemListener(this);
		rb2.addItemListener(this);
		rb3.addItemListener(this);
	}
	//事件处理方法,在产生ItemEvent事件是调用
	public void itemStateChanged(ItemEvent e)
	{
		//判断事件源是否是单选按钮
		if(e.getSource() instanceof JRadioButton)
		{
			//判断哪个单选按钮是否处于选中状态,如果选中则设置文本框的相应对齐方式
			if(rb1.isSelected())
				jtf.setHorizontalAlignment(JTextField.LEFT);
			if(rb2.isSelected())
				jtf.setHorizontalAlignment(JTextField.CENTER);
			if(rb3.isSelected())
				jtf.setHorizontalAlignment(JTextField.RIGHT);
		}	
	}
	public static void main(String[] args)
	{
		TestRadioButton frame = new TestRadioButton();
		frame.setSize(250,100);
		frame.setDefaultCloseOperation(3);
		frame.setVisible(true);
	}
}