使用Jcombobox更改项目后无法编辑jtable

Question

Im making a project about school management system , i have a jframe to set marks and inside the jframe i have a jtable which is connected to sql database , in the jframe i have a JCombobox with 6 different subjects and in my database i have created 6 tables for the subjects and if any of the subjects are clicked then the jTable will connect to database and change the table to that subject , after its changed if u double click on any row and insert a value then it will automatically update the table in the database , but my problem is that if i select the first option from the jcombox which is English and edit the values then it works fine , but if i select any other option eg Math or Science , then i try to edit the table then it edits the English table , I commented the English option in the code to see what happens and i saw that it edits only the first option and if u try to change the subjects and edit than it edits the first subject in the combobox , so how can i solve this ? please help

CODE:

import java.awt.EventQueue;
import javax.swing.JFrame;
import javax.swing.JLabel;
import java.awt.Font;
import javax.swing.JComboBox;
import javax.swing.JTable;
import javax.swing.JScrollPane;
import javax.swing.JButton;
import javax.swing.SwingConstants;
import javax.swing.JTextField;
import java.awt.Color;
import java.awt.List;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
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.ArrayList;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JMenuItem;
import javax.swing.JToolBar;
import javax.swing.event.TableModelEvent;
import javax.swing.event.*;
import javax.swing.table.TableModel;
import net.proteanit.sql.DbUtils;

public class Marks implements TableModelListener {

    JFrame frame;
    JTable table;
    JComboBox comboBox;
    static Connection connection = null;
    static Statement stmt = null;
    static ResultSet rs;
    String item = "";
    String id = "";
    String name = "";


    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    Marks window = new Marks();
                    window.frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    /**
     * Create the application.
     */
    public Marks() throws SQLException {

        connection = DriverManager.getConnection("jdbc:odbc:Project");

        initialize();
        table();
        ComboItem();
        stateChanged();    
        Combobox();
        item = comboBox.getSelectedItem().toString();
        System.out.println("Final Item: "+item);
    }

    public void table() {
        try {
            String a = comboBox.getSelectedItem().toString();
            //a = a.substring(0, a.length() - 1);
            String query = " Select * from " + a;
            PreparedStatement pst = connection.prepareStatement(query);
            rs = pst.executeQuery();
            table.setModel(DbUtils.resultSetToTableModel(rs));
            //item = comboBox.getSelectedItem().toString();

        } catch (Exception ex) {
            ex.printStackTrace();
        }

    }

    public void stateChanged(){
        itemListener = new ItemListener() {
            public void itemStateChanged(ItemEvent itemEvent) {
                System.out.println("Item after stateChanged: " + item);
                if (comboBox.getSelectedItem().equals("English")) {
                    try {
                        String query = "Select * from English";
                        PreparedStatement pst = connection.prepareStatement(query);
                        rs = pst.executeQuery();
                        table.setModel(DbUtils.resultSetToTableModel(rs));
                        table.getModel().addTableModelListener(new Marks());
                        item = "English";
                    } catch (Exception ex) {
                        ex.printStackTrace();
                    }

                }

                if (comboBox.getSelectedItem().equals("Math")) {
                    try {
                        String query = "Select * from Math";
                        PreparedStatement pst = connection.prepareStatement(query);
                        rs = pst.executeQuery();
                        table.setModel(DbUtils.resultSetToTableModel(rs));
                        table.getModel().addTableModelListener(new Marks());
                        item = "Math";
                    } catch (Exception ex) {
                        ex.printStackTrace();
                    }

                }

                if (comboBox.getSelectedItem().equals("Science")) {
                    try {
                        String query = "Select * from Science;";
                        PreparedStatement pst = connection.prepareStatement(query);
                        rs = pst.executeQuery();
                        table.setModel(DbUtils.resultSetToTableModel(rs));
                        table.getModel().addTableModelListener(new Marks());
                        item = "Science";
                    } catch (Exception ex) {
                        ex.printStackTrace();
                    }

                }

                if (comboBox.getSelectedItem().equals("History")) {
                    try {
                        String query = "Select * from History;";
                        PreparedStatement pst = connection.prepareStatement(query);
                        rs = pst.executeQuery();
                        table.setModel(DbUtils.resultSetToTableModel(rs));
                        table.getModel().addTableModelListener(new Marks());
                        item = "History";
                    } catch (Exception ex) {
                        ex.printStackTrace();
                    }

                }

                if (comboBox.getSelectedItem().equals("IT")) {
                    try {
                        String query = "Select * from IT;";
                        PreparedStatement pst = connection.prepareStatement(query);
                        rs = pst.executeQuery();
                        table.setModel(DbUtils.resultSetToTableModel(rs));
                        table.getModel().addTableModelListener(new Marks());
                        item = "IT";
                    } catch (Exception ex) {
                        ex.printStackTrace();
                    }

                }

                if (comboBox.getSelectedItem().equals("Geography")) {
                    try {
                        String query = "Select * from Geography;";
                        PreparedStatement pst = connection.prepareStatement(query);
                        rs = pst.executeQuery();
                        table.setModel(DbUtils.resultSetToTableModel(rs));
                        table.getModel().addTableModelListener(new Marks());
                        item = "Geography";
                    } catch (Exception ex) {
                        ex.printStackTrace();

                    }

                }
            }
        };
    }

    @Override
    public void tableChanged(TableModelEvent e) {

        try {
            int row = e.getFirstRow();
            int column = e.getColumn();
            TableModel model = (TableModel) e.getSource();
            String columnName = model.getColumnName(column);
            Object data = model.getValueAt(row, column);
            Object roll = model.getValueAt(row, 0);
            System.out.println("Subject Changed: " + item);
            System.out.println("New Data: " + data.toString());
            System.out.println("User Id: " + roll.toString());
            System.out.println("Column name: " + columnName);

            String query = "UPDATE " + item + " SET " + columnName + " = '"
                    + data.toString() + "' WHERE userid='" + roll.toString() + "' ";

            PreparedStatement pst;

            pst = connection.prepareStatement(query);

            pst.executeUpdate();
            // pst.close();
        } catch (SQLException ex) {
            Logger.getLogger(Marks.class.getName()).log(Level.SEVERE, null, ex);
            ex.printStackTrace();
        }

    }
    ItemListener itemListener;

    public void ComboItem(){        
        comboBox.addItemListener(itemListener);
    }

    private void Combobox() {
        comboBox.addItemListener(itemListener);

        comboBox.addKeyListener(new KeyAdapter() {
            public void keyReleased(KeyEvent e) {
                System.out.println(item);

               if (comboBox.getSelectedItem().equals("English")) {
                    try {
                        String query = "Select * from English";
                        PreparedStatement pst = connection.prepareStatement(query);
                        rs = pst.executeQuery();
                        table.setModel(DbUtils.resultSetToTableModel(rs));
                        table.getModel().addTableModelListener(new Marks());
                        item = "Engish";
                    } catch (Exception ex) {
                        ex.printStackTrace();
                    }

                }

                if (comboBox.getSelectedItem().equals("Math")) {
                    try {
                        String query = "Select * from Math";
                        PreparedStatement pst = connection.prepareStatement(query);
                        rs = pst.executeQuery();
                        table.setModel(DbUtils.resultSetToTableModel(rs));
                        table.getModel().addTableModelListener(new Marks());
                        item = "Math";
                    } catch (Exception ex) {
                        ex.printStackTrace();
                    }

                }

                if (comboBox.getSelectedItem().equals("Science")) {
                    try {
                        String query = "Select * from Science;";
                        PreparedStatement pst = connection.prepareStatement(query);
                        rs = pst.executeQuery();
                        table.setModel(DbUtils.resultSetToTableModel(rs));
                        table.getModel().addTableModelListener(new Marks());
                        item = "Science";
                    } catch (Exception ex) {
                        ex.printStackTrace();
                    }

                }

                if (comboBox.getSelectedItem().equals("History")) {
                    try {
                        String query = "Select * from History;";
                        PreparedStatement pst = connection.prepareStatement(query);
                        rs = pst.executeQuery();
                        table.setModel(DbUtils.resultSetToTableModel(rs));
                        table.getModel().addTableModelListener(new Marks());
                        item = "History";
                    } catch (Exception ex) {
                        ex.printStackTrace();
                    }

                }

                if (comboBox.getSelectedItem().equals("IT")) {
                    try {
                        String query = "Select * from IT;";
                        PreparedStatement pst = connection.prepareStatement(query);
                        rs = pst.executeQuery();
                        table.setModel(DbUtils.resultSetToTableModel(rs));
                        table.getModel().addTableModelListener(new Marks());
                        item = "IT";
                    } catch (Exception ex) {
                        ex.printStackTrace();
                    }

                }

                if (comboBox.getSelectedItem().equals("Geography")) {
                    try {
                        String query = "Select * from Geography;";
                        PreparedStatement pst = connection.prepareStatement(query);
                        rs = pst.executeQuery();
                        table.setModel(DbUtils.resultSetToTableModel(rs));
                        table.getModel().addTableModelListener(new Marks());
                        item = "Geography";
                    } catch (Exception ex) {
                        ex.printStackTrace();
                    }

                }

            }
        });
    }

    /**
     * Initialize the contents of the frame.
     */
    private void initialize() {
        frame = new JFrame();
        frame.getContentPane().setBackground(Color.WHITE);
        frame.setBounds(100, 100, 600, 400);
        frame.setResizable(false);
        frame.setLocationRelativeTo(null);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        //frame.setResizable(false);
        frame.getContentPane().setLayout(null);

        JLabel lblSetMarks = new JLabel("<html><u>Set Marks</u></html>");
        lblSetMarks.setHorizontalAlignment(SwingConstants.CENTER);
        lblSetMarks.setFont(new Font("Castellar", Font.BOLD, 25));
        lblSetMarks.setBounds(218, 11, 159, 22);
        frame.getContentPane().add(lblSetMarks);

        comboBox = new JComboBox();
        comboBox.setFont(new Font("Book Antiqua", Font.PLAIN, 15));
        comboBox.setBounds(459, 47, 125, 22);
        comboBox.addItem("English");
        comboBox.addItem("Geography");
        comboBox.addItem("History");
        comboBox.addItem("IT");
        comboBox.addItem("Math");
        comboBox.addItem("Science");
        frame.getContentPane().add(comboBox);

        JScrollPane scrollPane = new JScrollPane();
        scrollPane.setBounds(10, 87, 574, 259);
        frame.getContentPane().add(scrollPane);

        table = new JTable();

        scrollPane.setViewportView(table);

        JLabel lblClass = new JLabel("Date :");
        lblClass.setFont(new Font("Tahoma", Font.PLAIN, 15));
        lblClass.setBounds(10, 51, 58, 14);
        frame.getContentPane().add(lblClass);

        JLabel lblSubject = new JLabel("Subject :");
        lblSubject.setFont(new Font("Tahoma", Font.PLAIN, 15));
        lblSubject.setBounds(391, 49, 58, 18);
        frame.getContentPane().add(lblSubject);
    }
}

Answer 1

The problem revolves around the use of table.getModel().addTableModelListener(new Marks()); , which is creating a new instance of Marks , which your main class, each time you select a new project

This means that when tableChanged is called, it's not dealing with the instance of item which you modified in the original instance, but some other instance, which is ALWAYS set to English

Instead, you should try using something like table.getModel().addTableModelListener(this); instead, but only set it ONCE from within the constructor, otherwise it will be called multiple times, which will degrade the performance of your system...

Be Careful using a TableModelListener , it will be called when a cell is changed, row is changed, added, removed or the entire contents of the table model is changed. You should be trying to determine the actual type of event before trying to update the database, as you could end up updating the data to the wrong tables for the wrong reasons

You should avoid using null layouts, pixel perfect layouts are an illusion within modern ui design. There are too many factors which affect the individual size of components, none of which you can control. Swing was designed to work with layout managers at the core, discarding these will lead to no end of issues and problems that you will spend more and more time trying to rectify.

It would seriously discourage the use of a KeyListener on a JComboBox (I'd seriously discourage the use of KeyListener generally), it's not the best choice of listener for this case, besides, you now have two ItemListener s and a KeyListener attached to your combobox, all doing the same thing...multiple times...

Get rid of the ItemListener and use an ActionListener instead, ItemListener may be triggered multiple times (once for the deselection of the selected item and once of the selection of the new item) and frankly, you just don't care, you only want to know when it's changed.

Take a look at:

• Laying Out Components Within a Container
• How to Use Combo Boxes
• How to Write an Action Listeners

for more details