Why does my ItemStateChanged only change just once

[Jason Smit]

I have a strange problems. Perhaps some of you already have had this problem before.

I have method which is suppose to check if the itemstate has changed.
It ONLY works ONCE?

Thereafter, it does not matter how many times I changed the selection of the ComboBox.

---

Basically I have two Comboboxes.
1. If Combobox 1 is selected (e.g. Dogs, Cats)
2. Then get information from what ever the item from ComboBox 1 is selected, and display on ComboBox 2. (Dog Name, Cat Name etc)
e.g.
So If I selected Dogs on Combobox 1
Then display the Dog Names on Combobox 2.
If I then change and select Cats on Combobox 1,
then display Cat Names on ComboBox 2.

[Darryl Burke]

Impossible to guess without seeing the code. Please post a SSCCE.

[Jason Smit]

Darryl Burke wrote:Impossible to guess without seeing the code. Please post a SSCCE.

    private void SchemaJComboBoxItemStateChanged(java.awt.event.ItemEvent evt) {                                                 
        // TODO add your handling code here:
            
            try
            {   
                            
                            String username_ = Username_TxtBox.getText();
                            String password_ = String.valueOf(PasswordField_Masked_TxtBox.getPassword());
		
                            String thinConn = "jdbc:oracle:thin:@" + HostTxtBox.getText() + ":" + PortNoTxtBox.getText() + "/" + SIDTxtBox.getText();

                            conn_for_tables = DriverManager.getConnection(thinConn,username_,password_);
				
                            dbConnection = getDBConnection();
                            dbConnection.setAutoCommit(false);
           
                            stmt_for_tables = conn_for_tables.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_UPDATABLE);
                
                            String schema_name = String.valueOf(SchemaJComboBox.getSelectedItem());
                            String table_sql = "select table_name from all_tables where owner ='" + schema_name + "' order by table_name";
				
                            rs_for_tables = stmt_for_tables.executeQuery(table_sql);                
                                
                            String table_name = "Initialized";
                                
                            while (rs_for_tables.next())
                            {
                                    table_name = rs_for_tables.getString("table_name");
                                    TablesJComboBox.addItem(table_name);
                            }
			}
			catch (SQLException err)
			{
			
			}
			catch (NullPointerException ee)
			{
			
			}
    }

[Jason Smit]

I resolved the issue, I had to set the model of the 2nd Combobox to null:

private void SchemaJComboBoxItemStateChanged(java.awt.event.ItemEvent evt) {                                                 
        // TODO add your handling code here:
            
            try
            {   
                            TablesJComboBox.setModel(new javax.swing.DefaultComboBoxModel(new String[] {}));            
                
                            String username_ = Username_TxtBox.getText();
                            String password_ = String.valueOf(PasswordField_Masked_TxtBox.getPassword());
		
                            String thinConn = "jdbc:oracle:thin:@" + HostTxtBox.getText() + ":" + PortNoTxtBox.getText() + "/" + SIDTxtBox.getText();

                            conn_for_tables = DriverManager.getConnection(thinConn,username_,password_);
				
                            dbConnection = getDBConnection();
                            dbConnection.setAutoCommit(false);
           
                            stmt_for_tables = conn_for_tables.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_UPDATABLE);
                
                            String schema_name = String.valueOf(SchemaJComboBox.getSelectedItem());
                            String table_sql = "select table_name from all_tables where owner ='" + schema_name + "' order by table_name";
				
                            rs_for_tables = stmt_for_tables.executeQuery(table_sql);                
                                
                            String table_name = "Initialized";
                                
                            while (rs_for_tables.next())
                           {
                                    table_name = rs_for_tables.getString("table_name");
                                    TablesJComboBox.addItem(table_name);
                           }
			}
			catch (SQLException err)
			{
			
			}
			catch (NullPointerException ee)
			{
			
			}
    }                                                

[Rob Camick]

That is NOT a SSCCE. How can we compile/execute that code? How can we access your database.

The point of a SSCCE is simplify the problem. Usually, as you found out here, you will find the problem while you create the SSCCE.

[Darryl Burke]

Please note that, by convention, variable and method names in Java start with a lowercase letter, with subsequesnt words being capitalized, aka camelCase. Underscores are normaly used only as word separators in STATIC_FINAL_CONSTANTS

Failure to follow the convention can make it difficult for others to read and understand your code, and can directly affect the amount of help you get on any public forum.

Additionally, it's not good practice to mix JDBC and Swing code in the same class.

[Jason Smit]

Darryl Burke wrote:Please note that, by convention, variable and method names in Java start with a lowercase letter, with subsequesnt words being capitalized, aka camelCase. Underscores are normaly used only as word separators in STATIC_FINAL_CONSTANTS

Failure to follow the convention can make it difficult for others to read and understand your code, and can directly affect the amount of help you get on any public forum.

Additionally, it's not good practice to mix JDBC and Swing code in the same class.

Thanks for the tip,
Please show me examples of your code to illustrate your explanations.

[Rob Camick]

Please show me examples of your code to illustrate your explanations.

Look at code you find in any text book, or in the Swing tutorial or in answers given in the forum.

[Jason Smit]

Hi

I found this on the net:

/*
 * Copyright (c) 1995, 2008, Oracle and/or its affiliates. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 *   - Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *
 *   - Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *
 *   - Neither the name of Oracle or the names of its
 *     contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */ 

/**
 * This example, like all Swing examples, exists in a package:
 * in this case, the "start" package.
 * If you are using an IDE, such as NetBeans, this should work 
 * seamlessly.  If you are compiling and running the examples
 * from the command-line, this may be confusing if you aren't
 * used to using named packages.  In most cases,
 * the quick and dirty solution is to delete or comment out
 * the "package" line from all the source files and the code
 * should work as expected.  For an explanation of how to
 * use the Swing examples as-is from the command line, see
 * http://docs.oracle.com/javase/javatutorials/tutorial/uiswing/start/compile.html#package
 */
package start;

/*
 * HelloWorldSwing.java requires no other files. 
 */
import javax.swing.*;        

public class HelloWorldSwing {
    /**
     * Create the GUI and show it.  For thread safety,
     * this method should be invoked from the
     * event-dispatching thread.
     */
    private static void createAndShowGUI() {
        //Create and set up the window.
        JFrame frame = new JFrame("HelloWorldSwing");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        //Add the ubiquitous "Hello World" label.
        JLabel label = new JLabel("Hello World");
        frame.getContentPane().add(label);

        //Display the window.
        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        //Schedule a job for the event-dispatching thread:
        //creating and showing this application's GUI.
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI();
            }
        });
    }
}

I am right or wrong in saying that swing component/s should be placed on the main method of a script (i.e. public static void main(String[] args))?

And on methods?

[Campbell Ritchie]

You place Swing components on Containers or other Components. You mean should you put the code in a certain place? And what is this about scripts? That is a program not a script.

That is a very basic example you have found; it is the GUI equivalent of Hello World. At least it specifically starts the event despatch thread (EDT).
No, don't put GUI assembling code in the main method. The main method is for starting an application and should do nothing else. There are several place you can write code; I like to put it in the constructor for a GUI class. A method which sets up the GUI is another place you can put it.
I do not like extending GUI classes. You often have to override JLabel#paintComponent, but apart from that you should be able to create a GUI without using any inheritance beyond what Swing already uses. That example does exactly that. It creates instances of the classes and adds them to one another. Spot on. And in a good location.
That createGUI method is old‑fashioned. In Java5 (2004) the add method was altered so there is no longer any need to write getContentPane(). Also the method for starting the EDT was greately simplified in Java8 (2014) so there is no need for the anonymous class any more. In fact Horstmann in Core Java for the Impatient says you should no longer teach anonymous classes.

If you use Java8, you can change two of those statements to:-frame.add(label); //... SwingUtilities.invokeLater(() -> createAndShowGUI());