GridBagLayout gbl_centerPanel = new GridBagLayout();
        gbl_centerPanel.columnWidths = new int[]
        { 3, 1, 3 };
        gbl_centerPanel.rowHeights = new int[]
        { 1 };
        gbl_centerPanel.columnWeights = new double[]
        { 1.0, 0, 1.0 };
        gbl_centerPanel.rowWeights = new double[]
        { 1.0 };
        centerPanel.setLayout(gbl_centerPanel);

double[][] size = {
    {0.5, TableLayout.PREFERRED, 0.5},
    {TableLayout.FILL}
};
Container container = frame.getContentPane();
container .setLayout(new TableLayout(size));
container .add(new LeftPanel(), "0, 0");
container .add(new CenterPanel(), "1, 0");
container .add(new RightPanel(), "2, 0");

------解决方案--------------------

import java.awt.*;

import java.awt.event.*;

import javax.swing.*;

public class Calculator extends JFrame

{
   private JTextField displayField;// 计算结果显示区

   private String lastCommand;// 保存+,-,*,/,=命令

   private double result;// 保存计算结果

   private boolean start;// 判断是否为数字的开始



   private Container container;
   private GridBagLayout layout;
   private GridBagConstraints constraints;
   public Calculator()
   {
       super("java_刘阳");
       container = getContentPane();
       layout = new GridBagLayout();
       container.setLayout(layout);
       constraints = new GridBagConstraints();

       start = true;
       result = 0;
       lastCommand = "=";
       displayField = new JTextField(20);
       displayField.setHorizontalAlignment(JTextField.RIGHT);

//注意这里
       constraints.gridx =0;
       constraints.gridy =0;
       constraints.gridwidth = 3; //在第几格显示
       constraints.gridheight = 1;
       constraints.fill = GridBagConstraints.BOTH;
       constraints.weightx = 100;  //调整比例
       constraints.weighty = 100;
       layout.setConstraints(displayField, constraints);
       container.add(displayField);



       ActionListener insert = new InsertAction();
       ActionListener command = new CommandAction();



       addButton("Backspace", 0, 1, 2, 1, insert);

       addButton("CE", 2, 1, 1, 1, insert);

       addButton("C", 3, 1, 1, 1, insert);

       addButton("7", 0, 2, 1, 1, insert);

       addButton("8", 1, 2, 1, 1, insert);

       addButton("9", 2, 2, 1, 1, insert);

       addButton("/", 3, 2, 1, 1, command);
//
//        addButton("4", 0, 3, 1, 1, insert);
//
//        addButton("5", 1, 3, 1, 1, insert);
//
//        addButton("6", 2, 3, 1, 1, insert);

//        addButton("*", 3, 3, 1, 1, command);
//
//        addButton("1", 0, 4, 1, 1, insert);
//
//        addButton("2", 1, 4, 1, 1, insert);
//
//        addButton("3", 2, 4, 1, 1, insert);
//
//        addButton("-", 3, 4, 1, 1, command);
//
//        addButton("0", 0, 5, 1, 1, insert);
//
//        addButton("+/-", 1, 5, 1, 1, insert);// 只显示"-"号,"+"没有实用价值
//
//        addButton(".", 2, 5, 1, 1, insert);