无法使用GridBagLayout布局管理器获取等宽的列

import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class GridBagLayoutExample {
    public static void main(String[] args) {
        JFrame frame = new JFrame("GridBagLayout Example");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        
        JPanel panel = new JPanel();
        panel.setLayout(new GridBagLayout());
        
        GridBagConstraints constraints = new GridBagConstraints();
        constraints.fill = GridBagConstraints.HORIZONTAL;
        constraints.weightx = 1.0; // 设置列的权重
        
        JButton button1 = new JButton("Button 1");
        constraints.gridx = 0;
        constraints.gridy = 0;
        panel.add(button1, constraints);
        
        JButton button2 = new JButton("Button 2");
        constraints.gridx = 1;
        constraints.gridy = 0;
        panel.add(button2, constraints);
        
        JButton button3 = new JButton("Button 3");
        constraints.gridx = 2;
        constraints.gridy = 0;
        panel.add(button3, constraints);
        
        frame.add(panel);
        frame.pack();
        frame.setVisible(true);
    }
}