更改Java按钮GridBayLayout的大小

尝试使用此代码示例，并提出可能出现的任何问题：

import java.awt.*;import javax.swing.*;public class GridBagTest{    private String[] buttonText = { "C", ".", "/", "*", "7", "8", "9", "-", "4", "5", "6", "+", "1", "2", "3", "=", "0", "+/-" };    private JButton[] button = new JButton[18];    private int counter = 0;    private void createAndDisplayGUI()    {        Jframe frame = new Jframe("GridBagLayout Test");        frame.setDefaultCloseOperation(Jframe.EXIT_ON_CLOSE);        JPanel contentPane = new JPanel();        contentPane.setLayout(new BorderLayout());        JPanel northPanel = new JPanel();        northPanel.setLayout(new BorderLayout(2, 2));        JTextField tfield = new JTextField();        northPanel.add(tfield, BorderLayout.CENTER);        JPanel centerPanel = new JPanel();        centerPanel.setLayout(new GridBagLayout());        GridBagConstraints gbc = new GridBagConstraints();        gbc.anchor = GridBagConstraints.PAGE_START;        gbc.fill = GridBagConstraints.BOTH;        gbc.weightx = 1.0;        gbc.weighty = 1.0;        gbc.insets = new Insets(2, 2, 2, 2);        for (int i = 0; i < button.length; i++)        { System.out.println("Button Text : " + buttonText[i]); button[i] = new JButton(buttonText[i]);        }        for (int i = 0; i < 3; i++)        { for (int j = 0; j < 4; j++) {         gbc.gridx = j;         gbc.gridy = i;         centerPanel.add(button[counter++], gbc); }        }        gbc.gridx = 0;        gbc.gridy = 3;        centerPanel.add(button[counter++], gbc);        gbc.gridx = 1;        gbc.gridy = 3;        centerPanel.add(button[counter++], gbc);        gbc.gridx = 2;        gbc.gridy = 3;        centerPanel.add(button[counter++], gbc);        gbc.gridx = 3;        gbc.gridy = 3;          gbc.gridwidth = 1;        gbc.gridheight = 2;        centerPanel.add(button[counter++], gbc);        int count = counter;        System.out.println(button[--count].getText());        gbc.gridx = 0;        gbc.gridy = 4;        gbc.gridheight = 1;        gbc.gridwidth = 2;        centerPanel.add(button[counter++], gbc);        gbc.gridwidth = 1;        gbc.gridx = 2;        gbc.gridy = 4;        centerPanel.add(button[counter++], gbc);        contentPane.add(northPanel, BorderLayout.PAGE_START);        contentPane.add(centerPanel, BorderLayout.CENTER);        frame.setContentPane(contentPane);        frame.pack();        frame.setLocationByPlatform(true);        frame.setVisible(true);    }    public static void main(String... args)    {        SwingUtilities.invokeLater(new Runnable()        { public void run() {     new GridBagTest().createAndDisplayGUI(); }        });    }}

Here is the output :