jTable on netbeans GUI

Question

I need to add table in my Java program. I used netbeans GUI to help me create the program. But when I insert Table on it. It won't display the table. Here is my code : (please look at method setTableItemList() )

/*
* To change this template, choose Tools | Templates
* and open the template in the editor.
*/
package Program;

import java.awt.BorderLayout; 
import java.awt.CardLayout;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Date;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.table.DefaultTableModel;
import javax.swing.table.TableColumn;
import javax.swing.table.TableModel;
import javax.swing.JTable;

public class MainPage extends javax.swing.JFrame {

/**
 * Creates new form test
 */
public MainPage() {
    initComponents();
}
private Connection connect = null;
private Statement statement = null;
private PreparedStatement preparedStatement = null;
private ResultSet resultSet = null;
private JTable table;
private JScrollPane ScrollPane;
private JPanel topPanel;

/**
 * This method is called from within the constructor to initialize the form.
 * WARNING: Do NOT modify this code. The content of this method is always
 * regenerated by the Form Editor.
 */
@SuppressWarnings("unchecked")
// <editor-fold defaultstate="collapsed" desc="Generated Code">
private void initComponents() {

    contentPanel = new javax.swing.JPanel();
    jPanel2 = new javax.swing.JPanel();
    jLabel2 = new javax.swing.JLabel();
    jPanel1 = new javax.swing.JPanel();
    jLabel1 = new javax.swing.JLabel();
    jLabel3 = new javax.swing.JLabel();
    jTextField1 = new javax.swing.JTextField();
    jTextField2 = new javax.swing.JTextField();
    jLabel4 = new javax.swing.JLabel();
    jScrollPane1 = new javax.swing.JScrollPane();
    jTextArea1 = new javax.swing.JTextArea();
    jButton1 = new javax.swing.JButton();
    jPanel3 = new javax.swing.JPanel();
    jPanel4 = new javax.swing.JPanel();
    jMenuBar1 = new javax.swing.JMenuBar();
    jMenu1 = new javax.swing.JMenu();
    jMenuItem2 = new javax.swing.JMenuItem();
    jMenu2 = new javax.swing.JMenu();
    jMenuItem1 = new javax.swing.JMenuItem();
    jMenuItem3 = new javax.swing.JMenuItem();

    setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

    contentPanel.setLayout(new java.awt.CardLayout());

    jLabel2.setText("WELCOME TO .....");

    org.jdesktop.layout.GroupLayout jPanel2Layout = new org.jdesktop.layout.GroupLayout(jPanel2);
    jPanel2.setLayout(jPanel2Layout);
    jPanel2Layout.setHorizontalGroup(
        jPanel2Layout.createParallelGroup(org.jdesktop.layout.GroupLayout.LEADING)
        .add(jPanel2Layout.createSequentialGroup()
            .add(144, 144, 144)
            .add(jLabel2)
            .addContainerGap(166, Short.MAX_VALUE))
    );
    jPanel2Layout.setVerticalGroup(
        jPanel2Layout.createParallelGroup(org.jdesktop.layout.GroupLayout.LEADING)
        .add(jPanel2Layout.createSequentialGroup()
            .add(125, 125, 125)
            .add(jLabel2)
            .addContainerGap(184, Short.MAX_VALUE))
    );

    contentPanel.add(jPanel2, "card3");

    jLabel1.setText("ID");

    jLabel3.setText("Nama");

    jTextField1.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            jTextField1ActionPerformed(evt);
        }
    });

    jLabel4.setText("Keterangan");

    jTextArea1.setColumns(20);
    jTextArea1.setRows(5);
    jScrollPane1.setViewportView(jTextArea1);

    jButton1.setText("Submit");

    org.jdesktop.layout.GroupLayout jPanel1Layout = new org.jdesktop.layout.GroupLayout(jPanel1);
    jPanel1.setLayout(jPanel1Layout);
    jPanel1Layout.setHorizontalGroup(
        jPanel1Layout.createParallelGroup(org.jdesktop.layout.GroupLayout.LEADING)
        .add(jPanel1Layout.createSequentialGroup()
            .add(30, 30, 30)
            .add(jPanel1Layout.createParallelGroup(org.jdesktop.layout.GroupLayout.TRAILING)
                .add(jButton1)
                .add(jPanel1Layout.createSequentialGroup()
                    .add(jPanel1Layout.createParallelGroup(org.jdesktop.layout.GroupLayout.LEADING)
                        .add(jLabel1)
                        .add(jLabel3)
                        .add(jLabel4))
                    .add(24, 24, 24)
                    .add(jPanel1Layout.createParallelGroup(org.jdesktop.layout.GroupLayout.LEADING, false)
                        .add(jTextField1)
                        .add(jTextField2)
                        .add(jScrollPane1, org.jdesktop.layout.GroupLayout.DEFAULT_SIZE, 248, Short.MAX_VALUE))))
            .addContainerGap(42, Short.MAX_VALUE))
    );
    jPanel1Layout.setVerticalGroup(
        jPanel1Layout.createParallelGroup(org.jdesktop.layout.GroupLayout.LEADING)
        .add(jPanel1Layout.createSequentialGroup()
            .addContainerGap()
            .add(jPanel1Layout.createParallelGroup(org.jdesktop.layout.GroupLayout.BASELINE)
                .add(jLabel1)
                .add(jTextField1, org.jdesktop.layout.GroupLayout.PREFERRED_SIZE, org.jdesktop.layout.GroupLayout.DEFAULT_SIZE, org.jdesktop.layout.GroupLayout.PREFERRED_SIZE))
            .addPreferredGap(org.jdesktop.layout.LayoutStyle.UNRELATED)
            .add(jPanel1Layout.createParallelGroup(org.jdesktop.layout.GroupLayout.BASELINE)
                .add(jLabel3)
                .add(jTextField2, org.jdesktop.layout.GroupLayout.PREFERRED_SIZE, org.jdesktop.layout.GroupLayout.DEFAULT_SIZE, org.jdesktop.layout.GroupLayout.PREFERRED_SIZE))
            .add(18, 18, 18)
            .add(jPanel1Layout.createParallelGroup(org.jdesktop.layout.GroupLayout.LEADING)
                .add(jLabel4)
                .add(jScrollPane1, org.jdesktop.layout.GroupLayout.PREFERRED_SIZE, 152, org.jdesktop.layout.GroupLayout.PREFERRED_SIZE))
            .add(18, 18, 18)
            .add(jButton1)
            .addContainerGap(50, Short.MAX_VALUE))
    );

    contentPanel.add(jPanel1, "card2");

    org.jdesktop.layout.GroupLayout jPanel4Layout = new org.jdesktop.layout.GroupLayout(jPanel4);
    jPanel4.setLayout(jPanel4Layout);
    jPanel4Layout.setHorizontalGroup(
        jPanel4Layout.createParallelGroup(org.jdesktop.layout.GroupLayout.LEADING)
        .add(0, 400, Short.MAX_VALUE)
    );
    jPanel4Layout.setVerticalGroup(
        jPanel4Layout.createParallelGroup(org.jdesktop.layout.GroupLayout.LEADING)
        .add(0, 53, Short.MAX_VALUE)
    );

    org.jdesktop.layout.GroupLayout jPanel3Layout = new org.jdesktop.layout.GroupLayout(jPanel3);
    jPanel3.setLayout(jPanel3Layout);
    jPanel3Layout.setHorizontalGroup(
        jPanel3Layout.createParallelGroup(org.jdesktop.layout.GroupLayout.LEADING)
        .add(jPanel4, org.jdesktop.layout.GroupLayout.DEFAULT_SIZE, org.jdesktop.layout.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
    );
    jPanel3Layout.setVerticalGroup(
        jPanel3Layout.createParallelGroup(org.jdesktop.layout.GroupLayout.LEADING)
        .add(jPanel3Layout.createSequentialGroup()
            .addContainerGap(270, Short.MAX_VALUE)
            .add(jPanel4, org.jdesktop.layout.GroupLayout.PREFERRED_SIZE, org.jdesktop.layout.GroupLayout.DEFAULT_SIZE, org.jdesktop.layout.GroupLayout.PREFERRED_SIZE))
    );

    contentPanel.add(jPanel3, "card4");

    jMenu1.setText("File");

    jMenuItem2.setText("Home");
    jMenuItem2.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            jMenuItem2ActionPerformed(evt);
        }
    });
    jMenu1.add(jMenuItem2);

    jMenuBar1.add(jMenu1);

    jMenu2.setText("Edit");

    jMenuItem1.setText("Item");
    jMenuItem1.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            jMenuItem1ActionPerformed(evt);
        }
    });
    jMenu2.add(jMenuItem1);

    jMenuItem3.setText("ItemList");
    jMenuItem3.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            jMenuItem3ActionPerformed(evt);
        }
    });
    jMenu2.add(jMenuItem3);

    jMenuBar1.add(jMenu2);

    setJMenuBar(jMenuBar1);

    org.jdesktop.layout.GroupLayout layout = new org.jdesktop.layout.GroupLayout(getContentPane());
    getContentPane().setLayout(layout);
    layout.setHorizontalGroup(
        layout.createParallelGroup(org.jdesktop.layout.GroupLayout.LEADING)
        .add(org.jdesktop.layout.GroupLayout.TRAILING, contentPanel, org.jdesktop.layout.GroupLayout.DEFAULT_SIZE, org.jdesktop.layout.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
    );
    layout.setVerticalGroup(
        layout.createParallelGroup(org.jdesktop.layout.GroupLayout.LEADING)
        .add(contentPanel, org.jdesktop.layout.GroupLayout.DEFAULT_SIZE, org.jdesktop.layout.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
    );

    pack();
}// </editor-fold>

//Edit to see what are you searching
public void readDataBase() throws Exception {
    try {

        // This will load the MySQL driver, each DB has its own driver
        Class.forName("com.mysql.jdbc.Driver");
        // Setup the connection with the DB

        connect = DriverManager.getConnection("jdbc:mysql://localhost/amp", "root", "root");

        // Statements allow to issue SQL queries to the database
        statement = connect.createStatement();
        // Result set get the result of the SQL query
        resultSet = statement
                .executeQuery("select * from amp.barang");
        //writeResultSet(resultSet);

        while (resultSet.next()) {
            System.out.println(resultSet.getNString(1));
        }
        //writeMetaData(resultSet);
        // PreparedStatements can use variables and are more efficient

    } catch (Exception e) {
        throw e;
    } finally {
        close();
    }
}

//Show table + collumns name
private void writeMetaData(ResultSet resultSet) throws SQLException {
    //   Now get some metadata from the database
    // Result set get the result of the SQL query

    System.out.println("The columns in the table are: ");

    System.out.println("Table: " + resultSet.getMetaData().getTableName(1));
    for (int i = 1; i <= resultSet.getMetaData().getColumnCount(); i++) {
        System.out.println("Column " + i + " " + resultSet.getMetaData().getColumnName(i));
    }
}

//Edit to set in table
private void insertQueryBarang() throws Exception {
    try {

        // This will load the MySQL driver, each DB has its own driver
        Class.forName("com.mysql.jdbc.Driver");
        // Setup the connection with the DB

        connect = DriverManager.getConnection("jdbc:mysql://localhost/amp", "root", "root");

        // Statements allow to issue SQL queries to the database
        statement = connect.createStatement();
        // Result set get the result of the SQL query
        statement
                .executeUpdate("INSERT INTO `amp`.`barang` (`idbarang`,`namaBarang`,`keteranganBarang`) "
                + "VALUES ('02','B','this is B')");
        //writeResultSet(resultSet);

        //writeMetaData(resultSet);
        // PreparedStatements can use variables and are more efficient

    } catch (Exception e) {
        throw e;
    } finally {
        close();
    }

}

//See result
private void writeResultSet(ResultSet resultSet) throws SQLException {
    // ResultSet is initially before the first data set
    while (resultSet.next()) {
        // It is possible to get the columns via name
        // also possible to get the columns via the column number
        // which starts at 1
        // e.g. resultSet.getSTring(2);
        String user = resultSet.getString("myuser");
        String website = resultSet.getString("webpage");
        String summary = resultSet.getString("summary");
        Date date = resultSet.getDate("datum");
        String comment = resultSet.getString("comments");
        System.out.println("User: " + user);
        System.out.println("Website: " + website);
        System.out.println("Summary: " + summary);
        System.out.println("Date: " + date);
        System.out.println("Comment: " + comment);
    }
}

private void setTableItemList() {
    topPanel = new JPanel();
    topPanel.setLayout(new BorderLayout());
    getContentPane().add(topPanel);

    // Create columns names
    String columnNames[] = {"Column 1", "Column 2", "Column 3"};

    // Create some data
    String dataValues[][] = {
        {"12", "234", "67"},
        {"-123", "43", "853"},
        {"93", "89.2", "109"},
        {"279", "9033", "3092"}
    };

    // Create a new table instance
    table = new JTable(dataValues, columnNames);

    // Add the table to a scrolling pane
    ScrollPane = new JScrollPane(table);
    topPanel.add(ScrollPane, BorderLayout.CENTER);
    jPanel3.add(topPanel);
}

private void close() {
    try {
        if (resultSet != null) {
            resultSet.close();
        }

        if (statement != null) {
            statement.close();
        }

        if (connect != null) {
            connect.close();
        }
    } catch (Exception e) {
    }
}

private void jMenuItem1ActionPerformed(java.awt.event.ActionEvent evt) {                                           
    // TODO add your handling code here:
    CardLayout cl = (CardLayout) (contentPanel.getLayout());
    cl.show(contentPanel, "card2");
}                                          

private void jMenuItem2ActionPerformed(java.awt.event.ActionEvent evt) {                                           
    // TODO add your handling code here:
    CardLayout cl = (CardLayout) (contentPanel.getLayout());
    cl.show(contentPanel, "card3");
}                                          

private void jTextField1ActionPerformed(java.awt.event.ActionEvent evt) {                                            
    // TODO add your handling code here:
}                                           

private void jMenuItem3ActionPerformed(java.awt.event.ActionEvent evt) {                                           
    // TODO add your handling code here:
    CardLayout cl = (CardLayout) (contentPanel.getLayout());
    cl.show(contentPanel, "card4");
}                                          

/**
 * @param args the command line arguments
 */
public static void main(String args[]) throws Exception {
    /* Set the Nimbus look and feel */
    //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
    /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
     * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html 
     */
    try {
        for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
            if ("Nimbus".equals(info.getName())) {
                javax.swing.UIManager.setLookAndFeel(info.getClassName());
                break;
            }
        }
    } catch (ClassNotFoundException ex) {
        java.util.logging.Logger.getLogger(MainPage.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (InstantiationException ex) {
        java.util.logging.Logger.getLogger(MainPage.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (IllegalAccessException ex) {
        java.util.logging.Logger.getLogger(MainPage.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (javax.swing.UnsupportedLookAndFeelException ex) {
        java.util.logging.Logger.getLogger(MainPage.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    }
    //</editor-fold>

    /* Create and display the form */
    MainPage dao = new MainPage();
    //dao.insertQueryBarang();
    dao.readDataBase();
    dao.setTableItemList();
    java.awt.EventQueue.invokeLater(new Runnable() {
        public void run() {
            new MainPage().setVisible(true);
        }
    });
}
// Variables declaration - do not modify
private javax.swing.JPanel contentPanel;
private javax.swing.JButton jButton1;
private javax.swing.JLabel jLabel1;
private javax.swing.JLabel jLabel2;
private javax.swing.JLabel jLabel3;
private javax.swing.JLabel jLabel4;
private javax.swing.JMenu jMenu1;
private javax.swing.JMenu jMenu2;
private javax.swing.JMenuBar jMenuBar1;
private javax.swing.JMenuItem jMenuItem1;
private javax.swing.JMenuItem jMenuItem2;
private javax.swing.JMenuItem jMenuItem3;
private javax.swing.JPanel jPanel1;
private javax.swing.JPanel jPanel2;
private javax.swing.JPanel jPanel3;
private javax.swing.JPanel jPanel4;
private javax.swing.JScrollPane jScrollPane1;
private javax.swing.JTextArea jTextArea1;
private javax.swing.JTextField jTextField1;
private javax.swing.JTextField jTextField2;
// End of variables declaration
}

Answer 1

Couple of things:

1- If you're using GUI builder you can just add the table "visually" and fill it through its table model.

2- At this method:

private void setTableItemList() {
    topPanel = new JPanel();
    topPanel.setLayout(new BorderLayout());
    getContentPane().add(topPanel); // <-- topPanel added for first time

    // Create columns names
    String columnNames[] = {"Column 1", "Column 2", "Column 3"};    
    // Create some data
    String dataValues[][] = {
        {"12", "234", "67"},
        {"-123", "43", "853"},
        {"93", "89.2", "109"},
        {"279", "9033", "3092"}
    };

    // Create a new table instance
    table = new JTable(dataValues, columnNames);    
    // Add the table to a scrolling pane
    ScrollPane = new JScrollPane(table);
    topPanel.add(ScrollPane, BorderLayout.CENTER);
    jPanel3.add(topPanel); // <-- topPanel added second time to another container
}

You're adding topPanel in two different containers. From javadoc :

public Component add(Component comp)

Appends the specified component to the end of this container. This is a convenience method for addImpl(java.awt.Component, java.lang.Object, int).

This method changes layout-related information, and therefore, invalidates the component hierarchy. If the container has already been displayed, the hierarchy must be validated thereafter in order to display the added component.

So, if you want to add this topPanel directly into frame's content pane, then call frame.pack() method after adding it. If you want to add topPanel into jPanel3 then call jPanel3.validate() after adding it.