使用BoxLayout布局管理器代替默认的FlowLayout布局管理器，并在添加按钮之前设置组件垂直对齐方式和间距。示例代码如下：

import javax.swing.*;
import java.awt.*;

public class ButtonGroupTest extends JFrame {
    public ButtonGroupTest() {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JRadioButton btn1 = new JRadioButton("Button 1");
        JRadioButton btn2 = new JRadioButton("Button 2");
        JRadioButton btn3 = new JRadioButton("Button 3");
        JRadioButton btn4 = new JRadioButton("Button 4");
        JRadioButton btn5 = new JRadioButton("Button 5");

        // 创建一个垂直方向的BoxLayout布局管理器
        BoxLayout layout = new BoxLayout(getContentPane(), BoxLayout.Y_AXIS);
        getContentPane().setLayout(layout);

        // 按钮之间的垂直间距为20px
        getContentPane().add(Box.createVerticalStrut(20));

        // 设置组件对齐方式为左对齐
        JPanel panel = new JPanel(new FlowLayout(FlowLayout.LEFT));
        panel.add(btn1);
        panel.add(btn2);
        getContentPane().add(panel);

        getContentPane().add(Box.createVerticalStrut(20));

        // 设置组件对齐方式为右对齐
        panel = new JPanel(new FlowLayout(FlowLayout.RIGHT));
        panel.add(btn3);
        panel.add(btn4);
        getContentPane().add(panel);

        getContentPane().add(Box.createVerticalStrut(20));

        // 设置组件对齐方式为居中对齐
        panel = new JPanel(new FlowLayout(FlowLayout.CENTER));
        panel.add(btn5);
        getContentPane().add(panel);

        pack();
        setVisible(true);
    }

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