updating JList with DefaultListModel

Question

I am using an embedded database to query the name of an entry and put it in a JList . When the program runs, the list is populated fine.

I have made a function that is supposed to initialize and refresh the list called populateList() .

Here are the relevant parts of my code:

public class GUI extends JFrame{
    private int maxBankNr;
    private BankAccountDAO bankAccountDAO;
    private DBManager dbm;
    ...

    public GUI(){
        initComponents(); //sets up the Swing GUI
        this.dbm = new DBManager();
        this.bankAccountDAO = dbm.getBankAccountDAO();
        ...

        populateList();

    }

    private void populateList(){
        updateAll = false; //this seems to stop baAccountListValueChanged from throwing an exception
        this.maxBankNr = bankAccountDAO.getMaxBankNr(); //max number of bank accounts in database
        BankAccount ba;
        DefaultListModel dlm = new DefaultListModel();

        baAccountList.setModel(dlm);

        for(int i = 1; i <= this.maxBankNr; i++){
            ba = bankAccountDAO.getBankAccount(i);

            dlm.addElement(ba.getName());
        }

    updateAll = true;
}
...

private void baRefreshButtonActionPerformed(java.awt.event.ActionEvent evt){                                                
    populateList();
} 

...

My problem is that populateList() works fine when the program starts, but when it is called from baRefreshButtonActionPerformed , it appears to do nothing. The list stays exactly the same.

I have tried lots of different approaches, like using a Vector, using JList.setListData() , revalidating, validating and repainting all relevant containers. I have also tried using different types of ListModel .

Also, I have read that calling fireContentsChanged() should work, but DefaultListModel doesn't allow it, and I'm sure it gets called automatically anyway.

I have spent hours looking for a fix, most sites I've visited say the same things that I have tried, although none of them are working.

I hope this is enough information, let me know if you need to know anything else, thanks.

EDIT I have finally managed to fix this, much to my relief :D

It had nothing to do with my ListModel at all, but my BankAccountDAO class. This is the old version:

package com.accounts;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

public class BankAccountDAO {
private String insertBankAccountSQL =
        "INSERT INTO accounts.bankaccounts(bankNr, sortCode, accountNumber, balance, interest, details, name) " +
        "VALUES (?, ?, ?, ?, ?, ?, ?)";

private String getBankAccountSQL = 
        "SELECT bankNr, sortCode, accountNumber, balance, interest, details, name " +
        "FROM accounts.bankaccounts WHERE bankNr = ?";

private Connection conn = null;
private PreparedStatement pstmt = null;
private int maxBankNr = 0;

public BankAccountDAO(Connection theConn){
    this.conn = theConn;

    try{
        this.pstmt = conn.prepareStatement(getBankAccountSQL);

        Statement stmt = conn.createStatement();

        ResultSet rs = stmt.executeQuery("SELECT MAX(bankNr) FROM accounts.bankaccounts");

        if(rs.next()){
            maxBankNr = rs.getInt(1);

        }

        rs.close();
        stmt.close();
    }catch(SQLException se){
       printSQLException(se); 
    }
}

public int getMaxBankNr(){     
    return(this.maxBankNr);
}

public void insertBankAccount(int bankNr, int sortCode, int accountNumber, double balance, double interest, String details, String name){
    PreparedStatement ins = null;

    try{
        ins = conn.prepareStatement(insertBankAccountSQL);
        ins.setInt(1, bankNr);
        ins.setInt(2, sortCode);
        ins.setInt(3, accountNumber);
        ins.setDouble(4, balance);
        ins.setDouble(5, interest);
        ins.setString(6, details);
        ins.setString(7, name);

        ins.execute();
    }catch(SQLException se){
        printSQLException(se);
    }
}

public BankAccount getBankAccount(int targetBankNr){
    BankAccount ba = null;

    try{
        pstmt.clearParameters();
        pstmt = conn.prepareStatement(getBankAccountSQL);
        pstmt.setInt(1, targetBankNr);

        ResultSet rs = pstmt.executeQuery();

        if(rs.next()){
            int bankNr = rs.getInt("bankNr");
            int sortCode = rs.getInt("sortCode");
            int accountNumber = rs.getInt("accountNumber");
            double balance = rs.getDouble("balance");
            double interest = rs.getDouble("interest");
            String details = rs.getString("details");
            String name = rs.getString("name");

            ba = new BankAccount(bankNr, sortCode, accountNumber, balance, interest, details, name);

        }

        rs.close();
    }catch(SQLException se){
        printSQLException(se);
    }

    return ba;
}

private void printSQLException(SQLException se){
    while(se != null){

        System.out.print("SQLException: State: " + se.getSQLState());
        System.out.println("Severity:            " + se.getErrorCode());
        System.out.println(se.getMessage());

        se = se.getNextException();
    }
}
}

I have changed the getMaxBankNr() getter as follows:

public int getMaxBankNr(){
    try{
        Statement stmt = conn.createStatement();

        ResultSet rs = stmt.executeQuery("SELECT MAX(bankNr) FROM accounts.bankaccounts");


        if(rs.next()){
            maxBankNr = rs.getInt(1);

        }
    }catch(SQLException e){
        printSQLException(e);
    }

    return(this.maxBankNr);
}

When this.maxBankNr = bankAccountDAO.getMaxBankNr() was called, it wasn't returning an updated maxBankNr. This required a new SQL statement to return the proper value.

Anyone using a database with a list in the same way as me (i noticed quite a few people with the same problem as me while googling) should make sure that the for loop really knows how many times to loop.

I would have posted this as an answer, but I can't answer my own question for 8 hours, because I don't have enough points.

Answer 1

Hmm... This is a tough one. I think that that if populateList() works by itself, that baRefresButtonActionPerformed is not being executed itself.

I would try a regular ActionEvent and ActionPerformed as a listener or put some kind of output in it, like if baRefreshButtonActionPerformed , have it show a popup box saying the override has been executed.

Happy coding!

Answer 2

Normally you should call one of the following methods to notify the JList object of the changed data as apropriate:

fireContentsChanged(Object source, int index0, int index1)
fireIntervalAdded(Object source, int index0, int index1) 
fireIntervalRemoved(Object source, int index0, int index1)

Please check API doc for AbstractListModel .