单选按钮

构造ButtonGroup类型对象。

将JRadioButton对象添加到按钮组中。

new JRadioButton("Small",false)，第二个参数是初始状态。

buttonGroup.getSelection().getActionCommand()获得当前选中的按钮动作命令。

选择字体大小案例

package swing;

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.Toolkit;
import java.awt.event.ActionListener;

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

public class RadioButtonTest {

    private static final int DEFAULT_SIZE =36;
    private static JPanel buttonPanel = new JPanel();
    private static ButtonGroup buttonGroup = new ButtonGroup();
    private static JLabel label = new JLabel("敏捷的棕色狐狸跳过懒惰的狗.");
    
    public static void main(String[] args) {
        
        JFrame frame = new JFrame("单选按钮");
        
        label.setFont(new Font("Serif",Font.PLAIN,DEFAULT_SIZE));
        frame.add(label,BorderLayout.CENTER);
        
        addRadioButton("更小", 8);
        addRadioButton("中等", 12);
        addRadioButton("更大", 18);
        addRadioButton("巨大", 36);
        frame.add(buttonPanel,BorderLayout.SOUTH);
        
        frame.setSize(600, 400);
        //初始打开为屏幕中央
        Toolkit toolkit = Toolkit.getDefaultToolkit();
        Dimension screenSize = toolkit.getScreenSize();
        int screenWidth = (int) screenSize.getWidth();
        int screenHeight = (int) screenSize.getHeight();
        //计算窗口位置
        int x = (screenWidth - frame.getWidth())/2;
        int y = (screenHeight - frame.getHeight())/2;
        frame.setLocation(x, y);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }
    
    public static void addRadioButton(String name,int size) {
        boolean selected = size == DEFAULT_SIZE;
        var button = new JRadioButton(name, selected);
        buttonGroup.add(button);
        buttonPanel.add(button);
        ActionListener listener = e -> label.setFont(new Font("Serif", Font.PLAIN, size));
        button.addActionListener(listener);
    }

}