Java Swing jComboBox无法从数据库填充

Question

So I am working on a task force schedule for my mothers charity project. The aim is to check in the volunteers, display the roster for times and what station they are at. I have successfully built a login form, that pulls the data from the database and verify if your entered username (from dropdown) and password are correct. I have this method (NB: for the login form, it works and is not the problem) to fill the username dropdown called 'cbxUsername' which is called inside the main method when the window loads:

public void loginToProgram() throws Exception{
        user = (String) cbxUsername.getSelectedItem();
        if(user == "Please select a username"){
            JOptionPane.showMessageDialog(null, "Sorry, You need to select a username to continue");
        }else if(txtPassword.getText().length() == 0){
            JOptionPane.showMessageDialog(null, "Sorry, You need to enter a password to continue");
        } else {
            checkAuth();
        }

}

and then this method is refered to above, this is the checkAuth() method:

public void checkAuth() throws Exception{
    Class.forName("com.mysql.jdbc.Driver");

    Connection con = DriverManager.getConnection("jdbc:mysql://localhost/crm", "root", "t00rt00r");
    PreparedStatement statement = (PreparedStatement) con.prepareStatement("SELECT `password` FROM users WHERE `username` = '"+ user +"'");
    ResultSet result = statement.executeQuery();
    if(result.next() != false){
        pass = result.getString(1);
    }
    if(txtPassword.getText().equalsIgnoreCase(pass)){
        //JOptionPane.showMessageDialog(null, "Worked");
        CheckIn chk =  new CheckIn();

        chk.setVisible(true);
    } else {
        JOptionPane.showMessageDialog(null, "Sorry, wrong password");
    }
}

Now I have copied the first code (the method 'loginToProgram()') and altered it abit.

Now I have a new window called 'CheckIn', with a jComboBox called 'cbxCIFirstName'. The code to fill up this combobox is:

public static void fillFirstNameCombobox() throws Exception{
    Class.forName("com.mysql.jdbc.Driver");

    Connection con = (Connection) DriverManager.getConnection("jdbc:mysql://localhost/crm", "root", "t00rt00r");
    PreparedStatement statement = (PreparedStatement) con.prepareStatement("SELECT `first_name` FROM `volunteers`");
    ResultSet result = statement.executeQuery();
    cbxCIFirstName.setToolTipText("Select a first name");
    cbxCIFirstName.setEditable(true);
    cbxCIFirstName.addItem("Please Select a first name");
    while(result.next()){
        cbxCILastName.addItem(result.getString(1));
    }
    System.out.println(result.getString(1));
}

Please note: I put the System.out.println(result.getString(1)); there just to see if it was coming through in the console, and it is NOT coming through on the console. What am I doing wrong? Here is my Main method:

public static void main(String[] args) throws Exception{

    EventQueue.invokeLater(new Runnable() {
        public void run() {
            try {
                fillFirstNameCombobox();
                CheckIn frame = new CheckIn();
                frame.setVisible(true);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    });
}

Any suggestions will be greatly appreciated, any comments, guides, tutorials or anything I will take into consideration and try!

Thanks for your time, reading this post and thanks in advance for your answers, Josh.

Answer 1

public static void fillFirstNameCombobox() throws Exception{
    Class.forName("com.mysql.jdbc.Driver");

    Connection con = (Connection) DriverManager.getConnection("jdbc:mysql://localhost/crm", "root", "t00rt00r");
    PreparedStatement statement = (PreparedStatement) con.prepareStatement("SELECT `first_name` FROM `volunteers`");
    ResultSet result = statement.executeQuery();
    cbxCIFirstName.setToolTipText("Select a first name");
    cbxCIFirstName.setEditable(true);
    cbxCIFirstName.addItem("Please Select a first name");
    while(result.next()){
        cbxCILastName.addItem(result.getString(1)); 
    }
    System.out.println(result.getString(1));// this line can not be outside while loop
}

make this way

  public static void fillFirstNameCombobox() throws Exception{
        Class.forName("com.mysql.jdbc.Driver");

        Connection con = (Connection) DriverManager.getConnection("jdbc:mysql://localhost/crm", "root", "t00rt00r");
        PreparedStatement statement = (PreparedStatement) con.prepareStatement("SELECT first_name FROM volunteers");
        ResultSet result = statement.executeQuery();
        cbxCIFirstName.setToolTipText("Select a first name");
        cbxCIFirstName.setEditable(true);
        cbxCIFirstName.addItem("Please Select a first name");
        while(result.next()){
            cbxCILastName.addItem(result.getString(1)); 
System.out.println(result.getString(1));// this line can not be outside while loop
        }

}

REASON

Actually the cursor is at top level.When you are calling result.next) then the cursor comes down and at the end the cursor lies at bottom. That means at the end it return false and control comes out of while. You are trying to print after the while that means the cursor is already at the bottom so thats the problem.

Also the way you are using preparedstatement is not the right way. use this way

PreparedStatement statement = (PreparedStatement) con.prepareStatement("SELECT `password` FROM users WHERE `username` = ?);
statement.setString(1,user );

Answer 2

对于所有正在阅读此线程的人，我通过使用@javaBeginner提供的正确的prepareStatement方法（感谢）来修复它，然后从类的构造函数中调用它，而不是从主方法中调用方法“ fillFirstNameCombobox（）”，所以该类称为“ ClockIn”，我在构造函数/方法“ ClockIn（）”的最后一行调用了它