使用 DefaultModel 不显示 Java JTable 列标题

Question

正如标题所说，听众的名字只是没有出现。我尝试了很多选项，比如使用 JScrollPane。并在此论坛上提供了许多指南，但没有帮助。我真的很想自己解决问题，但我已经尝试了一切，但别无选择。

import java.awt.Color;
import java.awt.EventQueue;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JLabel;
import java.awt.Font;
import java.awt.ScrollPane;

import javax.swing.JButton;
import java.awt.event.ActionListener;
import java.sql.Connection;
import java.sql.DatabaseMetaData;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
import java.awt.event.ActionEvent;
import javax.swing.JTable;
import javax.swing.JTextField;
import javax.swing.table.DefaultTableModel;
import javax.swing.table.TableColumn;
import javax.swing.JScrollPane;
import javax.swing.JScrollBar;

public class Adminpage extends JPanel {
    private JFrame frame;
    static String ID[]={"name","Username","Password"};
    static DefaultTableModel model;
    private JTextField NametextField;
    private JTextField UsertextField;
    private JTextField PasstextField;
    private JTable table;
    private JScrollPane scroll;
    /**
     * Create the panel.
     */
    private void initialize() {
        frame = new JFrame();
        frame.setBounds(100, 100, 497, 545);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().setLayout(null);

        JLabel lblAdminstratorPortal = new JLabel("Adminstrator Portal");
        lblAdminstratorPortal.setFont(new Font("Tahoma", Font.BOLD, 20));
        lblAdminstratorPortal.setBounds(109, 26, 218, 25);
        frame.getContentPane().add(lblAdminstratorPortal);

        JButton btnNewButton = new JButton("Add Librarian");
        btnNewButton.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {
                //model= (DefaultTableModel)table.getModel();
                //model.addColumn("name");
                //model.addColumn("Username");
                //model.addColumn("Password");
                model.addRow(new Object[]{NametextField.getText(),UsertextField.getText(),PasstextField.getText()});

            }
        });
        btnNewButton.setBounds(10, 62, 108, 35);
        frame.getContentPane().add(btnNewButton);

        JButton btnDelete = new JButton("Delete");
        btnDelete.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {

            }
        });
        btnDelete.setBounds(130, 62, 108, 35);
        frame.getContentPane().add(btnDelete);

        JButton btnViewLibrarian = new JButton("View Librarian");
        btnViewLibrarian.setBounds(245, 62, 108, 35);
        frame.getContentPane().add(btnViewLibrarian);

        JButton btnLogout = new JButton("Logout");
        btnLogout.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {
                frame.dispose();
            }
        });
        btnLogout.setBounds(363, 62, 108, 35);
        frame.getContentPane().add(btnLogout);
        //model= (DefaultTableModel)table.getModel();

        JLabel lblName = new JLabel("Name");
        lblName.setBounds(21, 144, 60, 14);
        frame.getContentPane().add(lblName);

        JLabel lblUsername = new JLabel("Username");
        lblUsername.setBounds(21, 195, 60, 14);
        frame.getContentPane().add(lblUsername);

        JLabel lblPassword = new JLabel("Password");
        lblPassword.setBounds(21, 250, 60, 14);
        frame.getContentPane().add(lblPassword);

        NametextField = new JTextField();
        NametextField.setBounds(119, 141, 119, 20);
        frame.getContentPane().add(NametextField);
        NametextField.setColumns(10);

        UsertextField = new JTextField();
        UsertextField.setColumns(10);
        UsertextField.setBounds(119, 192, 119, 20);
        frame.getContentPane().add(UsertextField);

        PasstextField = new JTextField();
        PasstextField.setColumns(10);
        PasstextField.setBounds(119, 247, 119, 20);
        frame.getContentPane().add(PasstextField);


        table = new JTable();
        table.setBounds(10, 304, 461, 189);
        frame.getContentPane().add(table);


        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {

                    frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }
    public Adminpage() {
        database();
        setLayout(null);
        initialize();
        model= (DefaultTableModel)table.getModel();
        model.addColumn("name");
        model.addColumn("Username");
        model.addColumn("Password");






    }
    public void database(){
        try {
            Class.forName("sun.jdbc.odbc.JdbsOdbcDriver");
            Connection con = DriverManager.getConnection("jdbc:odbc:Games");
            Statement st = con.createStatement();
            String getquery = ("Select* from Games");
            ResultSet rs= st.executeQuery(getquery);
            while(rs.next()){
            System.out.println(rs.getString(2));
            }

        } catch (Exception e) {
            System.out.println(e.getMessage());

        }
    }
}

Answer 1

您正在将 JTable 直接添加到 GUI。相反，是的，您需要将 JTable 嵌入到 JScrollPane 的视口(viewport)中，然后将 JScrollPane 添加到 GUI。

例如:

    table = new JTable();
    JScrollPane scrollPane = new JScrollPane(table);
    // table.setBounds(10, 304, 461, 189);
    scrollPane.setBounds(10, 304, 461, 189);  // This is bad, but will leave for now
    // frame.getContentPane().add(table);
    frame.getContentPane().add(scrollPane);

另外，您使用空布局和绝对定位会损害您的 GUI，因为这可能会干扰组件充分和正确地显示自身以达到其自己的首选大小的能力。更好的方法是学习和使用布局管理器。

例如，当我在我的平台上运行你的程序时，我看到:

请注意，由于不允许按钮达到其首选大小，因此按钮无法显示其完整文本。

例如，将 BoxLayout 与一些嵌套的 JPanels 一起使用，其中一个使用 GridLayout(1, 0, 5, 0) 作为一行，列数可变，组件之间的水平间距为 5 磅，和另一个使用 GridBagLayout 的嵌套 JPanel，用于放置 JTextFields 和 JLabel，以及一些使用默认 FlowLayout 将组件居中的“包装器”JPanel...

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

import javax.swing.*;
import javax.swing.table.DefaultTableModel;

public class AdminPage2 extends JPanel {
    private static final long serialVersionUID = 1L;
    public static final String TITLE = "Administrator Portal";
    private static final Font TITLE_FONT = new Font("Tahoma", Font.BOLD, 20);
    private static final String[] COL_NAMES = {"Name", "User Name", "Password"};
    private int txtFieldCols = 20;
    private JTextField nameField = new JTextField(txtFieldCols);
    private JTextField userNameField = new JTextField(txtFieldCols);
    private JPasswordField passwordField = new JPasswordField(txtFieldCols);
    private DefaultTableModel tableModel = new DefaultTableModel(COL_NAMES, 0);
    private JTable table = new JTable(tableModel);
    private JScrollPane tableScrollPane = new JScrollPane(table);

    public AdminPage2() {
        JLabel titleLabel = new JLabel(TITLE, SwingConstants.CENTER);
        titleLabel.setFont(TITLE_FONT);
        JPanel titlePanel = new JPanel();
        titlePanel.add(titleLabel);

        JPanel buttonPanel = new JPanel(new GridLayout(1, 0, 5, 0));
        // of course you'd add ActionListeners or Actions to your buttons
        buttonPanel.add(new JButton("Add Library"));
        buttonPanel.add(new JButton("Delete"));
        buttonPanel.add(new JButton("View Library"));
        buttonPanel.add(new JButton("Logout"));

        JPanel textFieldPanel = new JPanel(new GridBagLayout());
        textFieldPanel.add(new JLabel("Name:"), createGbc(0, 0));
        textFieldPanel.add(nameField, createGbc(1, 0));
        textFieldPanel.add(new JLabel("User Name:"), createGbc(0, 1));
        textFieldPanel.add(userNameField, createGbc(1, 1));
        textFieldPanel.add(new JLabel("Password:"), createGbc(0, 2));
        textFieldPanel.add(passwordField, createGbc(1, 2));

        JPanel wrapTfPanel = new JPanel();
        wrapTfPanel.add(textFieldPanel);

        Dimension scrollPanePrefSz = tableScrollPane.getPreferredSize();
        int w = scrollPanePrefSz.width;
        int h = scrollPanePrefSz.height / 2;
         scrollPanePrefSz = new Dimension(w, h);
         tableScrollPane.setPreferredSize(scrollPanePrefSz);

        // put together main JPanel components
        int ebGap = 4;
        setBorder(BorderFactory.createEmptyBorder(ebGap, ebGap, ebGap, ebGap));
        setLayout(new BoxLayout(this, BoxLayout.PAGE_AXIS));
        add(Box.createVerticalStrut(5));
        add(titlePanel);
        add(Box.createVerticalStrut(5));
        add(buttonPanel);
        add(Box.createVerticalStrut(5));
        add(wrapTfPanel);
        add(Box.createVerticalStrut(5));
        add(tableScrollPane);
    }

    // create constraints to use when adding component to GridBagLayout
    private GridBagConstraints createGbc(int x, int y) {
        GridBagConstraints gbc = new GridBagConstraints();
        gbc.gridx = x;
        gbc.gridy = y;
        gbc.gridwidth = 1;
        gbc.gridheight = 1;
        gbc.weightx = 1.0;
        gbc.weighty = 1.0;
        gbc.anchor = x == 0 ? GridBagConstraints.WEST : GridBagConstraints.EAST;
        gbc.fill = GridBagConstraints.HORIZONTAL;
        int in = 10;
        int leftIn = x == 0 ? 4 * in : in;
        gbc.insets = new Insets(in, leftIn, in, in);
        return gbc;
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> createAndShowGui());
    }

    private static void createAndShowGui() {
        AdminPage2 mainPanel = new AdminPage2();
        JFrame frame = new JFrame("Administrator Page");
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        frame.add(mainPanel);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

}

显示为:

关于您的问题:

but new question why give the scrollpane a bound instead of the table itself

JScrollPane 在其中包含 JTable，因此如果您使用空布局(您不应该这样做)，并且您要将这个包含 JTable 的 JScrollPane 添加到 GUI，则必须设置它的界限。 好得多不过，使用我在上面概述的布局管理器会更好。这使得以后修改 GUI 和现在调试它变得更加容易。

and why adding the scrollpane into the panel instead of the table.

因为这就是 JScrollPanes 的工作方式。它们不向组件添加滚动条，而是将组件本身(此处为 JTable)嵌套在 JScrollPane 的视口(viewport)中。请阅读JScrollPane Tutorial (查看链接)查看详细信息。

---

关于布局管理器功能的进一步说明。假设您想添加一个新的 JLabel/JTextField 组合，一个接受密码提示的组合，并假设 JTextField 的名称是 passwordHint。如果您使用空布局和绝对定位，则必须设置新 JLabel 和 JTextField 的边界，但您还必须更改下方和右侧所有组件的边界它，并且必须手动重新设置 GUI 的大小。如果您的 GUI 非常复杂，这可能会导致错误和很多挫折。

但是，如果您使用了上面的布局管理器，您需要做的就是将两行代码添加到 textFieldPanel JPanel 创建代码中，如下所示，并带有明显的注释:

// original textFieldPanel creational code
JPanel textFieldPanel = new JPanel(new GridBagLayout());
textFieldPanel.add(new JLabel("Name:"), createGbc(0, 0));
textFieldPanel.add(nameField, createGbc(1, 0));
textFieldPanel.add(new JLabel("User Name:"), createGbc(0, 1));
textFieldPanel.add(userNameField, createGbc(1, 1));
textFieldPanel.add(new JLabel("Password:"), createGbc(0, 2));
textFieldPanel.add(passwordField, createGbc(1, 2));

// !! ****** these lines added ******
textFieldPanel.add(new JLabel("Password Hint:"), createGbc(0, 3));
textFieldPanel.add(passwordHint, createGbc(1, 3));

这会导致新组件的完美放置，而不会对旧组件产生不利影响: