Application is freezing when database is called

Question

I have lot of things implemented in ComponentAdapter of Java. Since it does loading data from database and displaying in JTable, I added it into another thread. I will show you one method which is being called by such ComponentAdapter

private class DisplayInitialRevenue_Thread implements Runnable
     {

        @Override
        public void run() 
        {
            displayInitialRevenue_Method();
        }

     }

     private void displayInitialRevenue_Method()
     {
        //Get the dates from the combo
        String selectedCouple = revenueYearCombo.getSelectedItem().toString();

        if(selectedCouple.equals("Select Year"))
        {
            return;
        }

        String[] split = selectedCouple.split("/");


         //Related to DB
         double totalamountInvested;



             //Get data from the database
             dbConnector = new DBHandler();
             dbConnector.makeConnection();

             DefaultTableModel model = (DefaultTableModel) initialRevenueTable.getModel();
             model.setRowCount(0);



             ResultSet selectAllDetails = dbConnector.selectAllDetails("SQL CODE HERE ");

             try
             {
                 if(selectAllDetails.isBeforeFirst()==false)
                 {
                     JOptionPane.showMessageDialog(null,"This table is empty");
                 }
                 else
                 {
                     while(selectAllDetails.next())
                     {
                         String clientName = selectAllDetails.getString("Client Name");
                         String providerName = selectAllDetails.getString("Provider Name");
                         Double amountInvested = selectAllDetails.getDouble("Invest_Amount");


                        //Get Other Data


                         //Update the table
                         Object[]row = {dateS,clientName,providerName,amountInvested};

                         model.addRow(row);

                         //Get the total
                         amountInvested = amountInvested+amountInvested;

                     }

                     //Add the sum
                     Object[]blankRow = {null,null,null,null};
                     model.addRow(blankRow);

                      Object[]row = {dateS,clientName,providerName,amountInvested};
                 }
             }
             catch(SQLException sql)
             {
                 JOptionPane.showMessageDialog(null,sql.getLocalizedMessage());
             }
     }

And, this above thread can be called in 3 ways. That is by ItemListener attached to a JComboBox, ActionListener attached to a JMenuand ComponentListener.

ComponentListener

private class DisplayInitialRevenue extends ComponentAdapter
     {
         public void componentShown(ComponentEvent e) 
         {
             formMemorizer = FormMemorizer.Initial_Revenue;
             //displayInitialRevenue_Method();

             DisplayInitialRevenue_Thread t = new DisplayInitialRevenue_Thread();
             t.run();
         }


     }

ItemListener

private class RevenueYearComboAction implements ItemListener
     {

        @Override
        public void itemStateChanged(ItemEvent e) 
        {
            if(e.getStateChange() == ItemEvent.SELECTED)
            {
                int selection = formMemorizer;

                if(selection==-1)
                {
                    return;
                }
                else if(selection==FormMemorizer.Initial_Revenue)
                {
                    //displayInitialRevenue_Method();
                    DisplayInitialRevenue_Thread t = new DisplayInitialRevenue_Thread();
                    t.run();
                }
        }
}

I have lot of these kind of methods to get the data from the database and feed the JTables and take data from GUI and save in database.

Now my question is, all of these are freezing sometimes, whenever a database call occurred. I thought it is bcs of Thread issue so I made the above DisplayInitialRevenue_Thread to call displayInitialRevenue_Method() as a test. Then I only invoked the area related to the call this method but it still freezes sometimes! My other database methods are not in separate threads, but this is method is, so why even calling "only" this method lead this to freeze? It is in a thread!

For side note, I am in Java 8, using MySQL Server version: 5.6.16 - MySQL Community Server (GPL) which comes with XAMPP.

Answer 1

Call t.start() to start a new Thread, calling Thread#run does nothing more then calls the run method of the Thread within the same thread context...

Having said that, Swing is not thread safe, Swing requires that all updates to the UI are made from within the context of the Event Dispatching Thread. Instead of using a Thread, you should consider using a SwingWorker, which allows you to execute long running tasks in a background thread, but which provides easy to use publish/process methods and calls done when it completes, which are executed within the context of the EDT for you.

See Worker Threads and SwingWorker for more details