Home » Developer & Programmer » JDeveloper, Java & XML » Error: Could not find or load main class main.java (java version "18.0.1.1" 2022-04-22)
Error: Could not find or load main class main.java [message #690195] Thu, 21 November 2024 13:47
wtolentino
Messages: 421
Registered: March 2005
Senior Member
I am new to Java and trying to compile this code but run into this errors:

java -cp .;C:\app\client\myAcct\product\19.0.0\client_1\jdbc\lib\ojdbc8.jar main.java

main.java:7: error: cannot find symbol
                new LoginScreen();
                    ^
  symbol: class LoginScreen
1 error
error: compilation failed

Main.java
import javax.swing.*;

public class Main {
    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                new LoginScreen();
            }
        });
    }
}

LoginSCreen.java
import javax.swing.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

public class LoginScreen extends JFrame {
    private JTextField usernameField;
    private JPasswordField passwordField;
    public static String user;
    public static String password;

    public LoginScreen() {
        setTitle("Login");
        setSize(300, 150);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLocationRelativeTo(null);

        JPanel panel = new JPanel();
        add(panel);
        placeComponents(panel);

        setVisible(true);
    }

    private void placeComponents(JPanel panel) {
        panel.setLayout(null);

        JLabel userLabel = new JLabel("User:");
        userLabel.setBounds(10, 20, 80, 25);
        panel.add(userLabel);

        usernameField = new JTextField(20);
        usernameField.setBounds(100, 20, 165, 25);
        panel.add(usernameField);

        JLabel passwordLabel = new JLabel("Password:");
        passwordLabel.setBounds(10, 50, 80, 25);
        panel.add(passwordLabel);

        passwordField = new JPasswordField(20);
        passwordField.setBounds(100, 50, 165, 25);
        panel.add(passwordField);

        JButton loginButton = new JButton("Login");
        loginButton.setBounds(10, 80, 80, 25);
        panel.add(loginButton);

        loginButton.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                String userInput = usernameField.getText();
                String passInput = new String(passwordField.getPassword());

                if (authenticate(userInput, passInput)) {
                    dispose();
                    new DataEntryScreen();
                } else {
                    JOptionPane.showMessageDialog(null, "Invalid login. Please try again.");
                }
            }
        });
    }

    private boolean authenticate(String userInput, String passInput) {
        user = userInput;
        password = passInput;
        String url = "jdbc:oracle:thin:@//host:1521/DEV";

        try (Connection conn = DriverManager.getConnection(url, user, password)) {
            return conn != null;
        } catch (SQLException e) {
            e.printStackTrace();
            return false;
        }
    }
}


DataEntryScreen.java
import java.sql.*;
import javax.swing.*;


public class DataEntryScreen extends JFrame {
    private JComboBox<String> tableDropdown;
    private JTextField usernameField;
    private JTextField firstNameField;
    private JTextField middleNameField;
    private JTextField lastNameField;
    private JTextField emailField;
    private JTable dataTable;

    public DataEntryScreen() {
        setTitle("User Account Reference Data Entry");
        setSize(800, 500);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLocationRelativeTo(null);

        JPanel panel = new JPanel();
        add(panel);
        placeComponents(panel);

        setVisible(true);
    }

    private void placeComponents(JPanel panel) {
        panel.setLayout(null);

        JLabel tableLabel = new JLabel("Select Table:");
        tableLabel.setBounds(10, 10, 100, 25);
        panel.add(tableLabel);

        tableDropdown = new JComboBox<>();
        tableDropdown.setBounds(120, 10, 200, 25);
        loadTables(); // Load table names dynamically
        panel.add(tableDropdown);

        JButton showDataButton = new JButton("Show Data");
        showDataButton.setBounds(330, 10, 120, 25);
        panel.add(showDataButton);
        showDataButton.addActionListener(e -> showTableData());

        JLabel usernameLabel = new JLabel("Username:");
        usernameLabel.setBounds(10, 50, 100, 25);
        panel.add(usernameLabel);

        usernameField = new JTextField(20);
        usernameField.setBounds(120, 50, 165, 25);
        panel.add(usernameField);

        JLabel firstNameLabel = new JLabel("First Name:");
        firstNameLabel.setBounds(10, 90, 100, 25);
        panel.add(firstNameLabel);

        firstNameField = new JTextField(20);
        firstNameField.setBounds(120, 90, 165, 25);
        panel.add(firstNameField);

        JLabel middleNameLabel = new JLabel("Middle Name:");
        middleNameLabel.setBounds(10, 130, 100, 25);
        panel.add(middleNameLabel);

        middleNameField = new JTextField(20);
        middleNameField.setBounds(120, 130, 165, 25);
        panel.add(middleNameField);

        JLabel lastNameLabel = new JLabel("Last Name:");
        lastNameLabel.setBounds(10, 170, 100, 25);
        panel.add(lastNameLabel);

        lastNameField = new JTextField(20);
        lastNameField.setBounds(120, 170, 165, 25);
        panel.add(lastNameField);

        JLabel emailLabel = new JLabel("Email Address:");
        emailLabel.setBounds(10, 210, 100, 25);
        panel.add(emailLabel);

        emailField = new JTextField(20);
        emailField.setBounds(120, 210, 165, 25);
        panel.add(emailField);

        JButton insertButton = new JButton("Insert");
        insertButton.setBounds(10, 260, 80, 25);
        panel.add(insertButton);
        insertButton.addActionListener(e -> insertData());

        /*JButton deleteButton = new JButton("Delete");
        deleteButton.setBounds(100, 260, 80, 25);
        panel.add(deleteButton);
        deleteButton.addActionListener(e -> deleteData());

        JButton updateButton = new JButton("Update");
        updateButton.setBounds(190, 260, 80, 25);
        panel.add(updateButton);
        updateButton.addActionListener(e -> updateData());*/

        dataTable = new JTable();
        JScrollPane scrollPane = new JScrollPane(dataTable);
        scrollPane.setBounds(10, 300, 760, 150);
        panel.add(scrollPane);
    }

    private void loadTables() {
        String url = "jdbc:oracle:thin:@//host:1521/DEV";

        try (Connection conn = DriverManager.getConnection(url, LoginScreen.user, LoginScreen.password)) {
            DatabaseMetaData metaData = conn.getMetaData();
            ResultSet tables = metaData.getTables(null, null, "%", new String[] {"TABLE"});

            while (tables.next()) {
                String tableName = tables.getString("TABLE_NAME");
                String table_schem = tables.getString("TABLE_SCHEM");
                tableDropdown.addItem(table_schem + "." + tableName); // Add table name to the dropdown
            }
        } catch (SQLException e) {
            e.printStackTrace();
            JOptionPane.showMessageDialog(this, "Error loading tables: " + e.getMessage());
        }
    }

    private void showTableData() {
    String selectedTable = (String) tableDropdown.getSelectedItem();
    String url = "jdbc:oracle:thin:@//host:1521/DEV"

    try (Connection conn = DriverManager.getConnection(url, LoginScreen.user, LoginScreen.password)) {
        String query = "SELECT * FROM " + selectedTable;
        PreparedStatement stmt = conn.prepareStatement(query);
        ResultSet rs = stmt.executeQuery();

        ResultSetMetaData metaData = rs.getMetaData();
        int columnCount = metaData.getColumnCount();

        // Fetch column names
        String[] columnNames = new String[columnCount];
        for (int i = 1; i <= columnCount; i++) {
            columnNames[i - 1] = metaData.getColumnName(i);
        }

        // Fetch rows dynamically
        java.util.List<Object[]> rows = new java.util.ArrayList<>();
        while (rs.next()) {
            Object[] rowData = new Object[columnCount];
            for (int colIndex = 0; colIndex < columnCount; colIndex++) {
                rowData[colIndex] = rs.getObject(colIndex + 1);
            }
            rows.add(rowData);
        }

        // Convert list to array for JTable
        Object[][] data = rows.toArray(new Object[0][]);

        // Update table model
        dataTable.setModel(new javax.swing.table.DefaultTableModel(data, columnNames));
    } catch (SQLException e) {
        e.printStackTrace();
        JOptionPane.showMessageDialog(this, "Error displaying data: " + e.getMessage());
    }
    }


    private void insertData() {
        executeQuery("INSERT INTO " + tableDropdown.getSelectedItem() +
                " (USERNAME, FIRST_NAME, MIDDLE_NAME, LAST_NAME, EMAIL_ADDRESS) VALUES (?, ?, ?, ?, ?)",
                true);
    }

   /*private void deleteData() {
        executeQuery("DELETE FROM " + tableDropdown.getSelectedItem() + " WHERE USERNAME = ?", false);
    }

    private void updateData() {
        executeQuery("UPDATE " + tableDropdown.getSelectedItem() +
                " SET EMAIL_ADDRESS = ? WHERE USERNAME = ?", false);
    }*/

    private void executeQuery(String query, boolean isInsert) {
        String url = "jdbc:oracle:thin:@//host:1521/DEV";

        try (Connection conn = DriverManager.getConnection(url, LoginScreen.user, LoginScreen.password);
             PreparedStatement stmt = conn.prepareStatement(query)) {

            stmt.setString(1, usernameField.getText());
            if (isInsert) {
                stmt.setString(2, firstNameField.getText());
                stmt.setString(3, middleNameField.getText());
                stmt.setString(4, lastNameField.getText());
                stmt.setString(5, emailField.getText());
            } else {
                stmt.setString(2, emailField.getText());
            }
            stmt.executeUpdate();

            JOptionPane.showMessageDialog(this, "Operation successful.");
        } catch (SQLException e) {
            e.printStackTrace();
            JOptionPane.showMessageDialog(this, "Error: " + e.getMessage());
        }
    }
}

However, when I asked a co-worker to compile it on her machine it is working. I am not sure what is missing. Please advise. Thank you.
Previous Topic: Not possible to connect via Java application (JDBC driver) but SQLplus connects
Goto Forum:
  


Current Time: Thu Dec 12 21:00:00 CST 2024