使用GridBagLayout如何让组件跨多列？Java Swing计算器布局问题

问题根因 #

该问题由GridBagLayout的权重分配规则导致：
你给所有组件设置了相同的weightx值，跨2列的文本框权重会被拆分到它覆盖的后两列，最终三列实际权重比例不相等，加上文本框本身首选宽度远大于按钮，初始列宽计算就会出现偏差，拉伸时第一列就会出现异常的尺寸变动。

修复方案 #

仅需调整weightx的配置，保证三列权重完全相等即可：

• 所有单列组件的weightx统一设为1（权重为相对比例，不需要设置过大的数值）
• 跨2列的文本框单独设置weightx=2，这样它覆盖的两列各分到1的权重，和第一列权重完全相等

修改后完整代码 #

import java.awt.Font;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;

import javax.swing.*;

public class Calculator extends JFrame{

    JButton but1, but2, but3, but4, but5, but6,
        but7, but8, but9, but0, butPlus, butMinus,
        clearAll;

    JTextField textResult;

    int num1, num2;

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

    public Calculator(){
            
        this.setSize(400,400);
        this.setLocationRelativeTo(null);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setTitle("Calculator");
    
        JPanel thePanel = new JPanel();
    
        thePanel.setLayout(new GridBagLayout());
    
        GridBagConstraints gridConstraints = new GridBagConstraints();
    
        gridConstraints.gridx = 0;
        gridConstraints.gridy = 0;
        gridConstraints.gridwidth = 1;
        gridConstraints.gridheight = 1;
        // 调整weightx和weighty为相对比例值
        gridConstraints.weightx = 1;
        gridConstraints.weighty = 1;
        gridConstraints.insets = new Insets(5, 5, 5, 5);
        gridConstraints.anchor = GridBagConstraints.CENTER;
        gridConstraints.fill = GridBagConstraints.BOTH;
    
        textResult = new JTextField("0", 20);
    
        Font font = new Font("Helvetica", Font.PLAIN, 18);
        textResult.setFont(font);
        // 可选优化：文本右对齐，禁止直接编辑，更符合计算器使用习惯
        textResult.setHorizontalAlignment(JTextField.RIGHT);
        textResult.setEditable(false);
    
        but1 = new JButton("1");
        but2 = new JButton("2");
        but3 = new JButton("3");
        but4 = new JButton("4");
        but5 = new JButton("5");
        but6 = new JButton("6");
        but7 = new JButton("7");
        but8 = new JButton("8");
        but9 = new JButton("9");
        butPlus = new JButton("+");
        but0 = new JButton("0");
        butMinus = new JButton("-");
        clearAll = new JButton("C");
    
        thePanel.add(clearAll, gridConstraints);
        gridConstraints.gridx = 1;
        gridConstraints.gridwidth = 2;
        // 跨2列的文本框单独设置weightx为2，保证覆盖的两列各分1权重
        gridConstraints.weightx = 2;
    
        thePanel.add(textResult, gridConstraints);
        gridConstraints.gridwidth = 1;
        // 恢复单列组件的weightx为1
        gridConstraints.weightx = 1;
        gridConstraints.gridx = 0;
        gridConstraints.gridy = 1;
        thePanel.add(but1, gridConstraints);
        gridConstraints.gridx = 1;
        thePanel.add(but2, gridConstraints);
        gridConstraints.gridx = 2;
        thePanel.add(but3, gridConstraints);
        gridConstraints.gridx = 0;
        gridConstraints.gridy = 2;
        thePanel.add(but4, gridConstraints);
        gridConstraints.gridx = 1;
        thePanel.add(but5, gridConstraints);
        gridConstraints.gridx = 2;
        thePanel.add(but6, gridConstraints);
        gridConstraints.gridx = 0;
        gridConstraints.gridy = 3;
        thePanel.add(but7, gridConstraints);
        gridConstraints.gridx = 1;
        thePanel.add(but8, gridConstraints);
        gridConstraints.gridx = 2;
        thePanel.add(but9, gridConstraints);
        gridConstraints.gridx = 0;
        gridConstraints.gridy = 4;
        thePanel.add(butPlus, gridConstraints);
        gridConstraints.gridx = 1;
        thePanel.add(but0, gridConstraints);
        gridConstraints.gridx = 2;
        thePanel.add(butMinus, gridConstraints);
    
        this.add(thePanel);
    
        this.setVisible(true);
    }
}

修改后无论怎么拉伸窗口，三列都会保持1:1:1的等宽比例，第一列组件不会再出现异常尺寸变动，文本框也会正常跨2列展示。

内容的提问来源于stack exchange，提问作者Zare