how to auto update jcombobox?

[Punit Jain]

i have a application, which has one registration panel, and one search panel..
i have a menu and on click of that menu i m changing the jpanel (registration or search).
on the search page i have one combo which displaying all the names of students who are registered or exist in the database.
but when i register a student and than click on search menu, it wiill not update the combo box, i mean the recently registered student is not appear in the list until i restart my application.
what i need to do to update the combo box automatically??

[Michael Dunn]

there are a few ways this could be done, this is one way:

create a method for when the program opens loadStudents()
in this you retrieve the student names
you load those names into a DefaultComboBoxModel()
you set the comboBox's model to the new DefaultComboBoxModel

you will also have a method to save the new student to the database saveStudent()

so, at the end of them registration process method, you call those methods

registrationProcess()
{
  ...
  ...
  saveStudent();
  loadStudents();
}

unless you have a huge quantity in the db, the above should work fine

[Punit Jain]

thank you for reply michael..
after getting all the values, i m sending them with insert method for insert into db, like this in my registration page,:

Db d = new Db();
					d.Insert(generalRegistrationNumber,firstName,address,religion,nationality,birthPlace,lastSchool,category,
							admittedClass,progress,conduct,leavingStudies,leavingCollegeReason, feeDue, fDate, fDate1,fDate2, fDate3);

in my search page i m fetching values something like this:

studentName = new JComboBox();
		studentName.setPreferredSize(new Dimension(160,20));
		res = db.NameValues();		
		studentName.setEditable(true);
		while(res.next()){						
			studentName.addItem(res.getString("names"));			
		}	

and here is my method which fetches names from database.

public ResultSet NameValues() throws SQLException{
		Statement ps;
		ResultSet res;
		String query  = "SELECT names FROM studentregistration";
		DbConnection dbconn = new DbConnection();
		Connection conn = dbconn.dbConn();		
		ps = conn.createStatement();
		res = ps.executeQuery(query);		
		return res;
	}

so can i use this method in my registration page also, if i use my problem is still remains same.
also can i use JComboBox instead of DefaultComboBoxModel, as i m doing..

while(res.next()){						
			studentName.addItem(res.getString("names"));			
		}	

[Michael Dunn]

instead of

while(res.next()){                        
     studentName.addItem(res.getString("names"));              
}    

use the 'model'

DefaultComboBoxModel model = new DefaultComboBoxModel();
while(res.next()){                        
     model.addElement(res.getString("names"));              
}    
studentName.setModel(model);

[Punit Jain]

not working..
i am doing something like this:
In my registration page:

Db d = new Db();
					d.Insert(generalRegistrationNumber,firstName,address,religion,nationality,birthPlace,lastSchool,category,
							admittedClass,progress,conduct,leavingStudies,leavingCollegeReason, feeDue, fDate, fDate1,fDate2, fDate3);
					d.RegistrationNumberValues();
					d.NameValues();

in my SearchByregistration page:

res = db.RegistrationNumberValues();
		DefaultComboBoxModel model = new DefaultComboBoxModel();
		while(res.next()){						
			     model.addElement(res.getString(1));                			   			 
		}				
		generalregnum.setModel(model);

[Michael Dunn]

> not working..

please read the text from this link --> It-Doesnt-Work-Is-Useless

easiest way is to show you a simple demo (using arraylist to simulate database)
enter some text into the textfield, click the button, open the comboBox

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.util.*;
class Testing
{
  java.util.List<Student> database = new ArrayList<Student>(Arrays.asList(new Student[]{new Student("Fred"),new Student("Mary"),new Student("Joe")}));
  JComboBox studentNames = new JComboBox();
  JTextField tf = new JTextField();
  public void buildGUI()
  {
    loadStudents();
    JButton btn = new JButton("Add New Student Name");
    JPanel p = new JPanel(new GridLayout(3,1));
    p.add(studentNames); p.add(tf);p.add(btn);
    JFrame f = new JFrame();
    f.getContentPane().add(p);
    f.pack();
    f.setLocationRelativeTo(null);
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    f.setVisible(true);
    btn.addActionListener(new ActionListener(){
      public void actionPerformed(ActionEvent ae){
        saveStudent();
      }
    });
  }
  public void loadStudents()
  {
    DefaultComboBoxModel model = new DefaultComboBoxModel();
    ListIterator iter = database.listIterator();
    while (iter.hasNext())
    {
      model.addElement(((Student)iter.next()).name);
    }
    studentNames.setModel(model);
  }
  public void saveStudent()
  {
    database.add(new Student(tf.getText()));//needs error handling
    tf.setText("");
    loadStudents();
  }
  public static void main(String[] args)
  {
    SwingUtilities.invokeLater(new Runnable(){
      public void run(){
        new Testing().buildGUI();
      }
    });
  }
}
class Student
{
  String name;
  public Student(String nm){name = nm;}
}

[Punit Jain]

hii, i read this..

please read the text from this link --> It-Doesnt-Work-Is-Useless

thank you for the demo..it's working, i am able to updating values from database, but when i am distributing the code i m getting some problems, it's going to be an infinite loop, can you please help me in this also.
here is what i am doing.
i m distributing this into three classes.
1.> which has methods to fetch from database and insert into database.
2.>which has my registration page.
3.>which has my display page.

here is how i am distributing the code:

CustomerLayout.java(Registration page)

public class CustomerLayout{
java.util.List<String> listNames = new ArrayList<String>();
public class Register implements ActionListener	
{
public void actionPerformed(ActionEvent e)	
		{
			if(e.getSource()==btnRegister)
			{
				try{
					saveStudent();
				}
				catch(Exception e1){
					e1.printStackTrace();
				}				
			}
		}
}

 public ArrayList<String> saveStudent() throws ClassNotFoundException, SQLException
	  {		
	    SearchByName sn = new SearchByName();
	    String ab = txtName.getText();
	    listNames.add(ab);//needs error handling
	    new Db().Insert(ab);
	    txtName.setText("");
	    System.out.println("Going");
	    sn.loadStudents();
	    return (ArrayList<String>) listNames;
	  }	  
}

Db.java (Database operations)

public class Db{
public ResultSet NameValues() throws SQLException{
		Statement ps;
		ResultSet res;
		String query  = "SELECT names FROM studentregistration";
		DbConnection dbconn = new DbConnection();
		Connection conn = dbconn.dbConn();		
		ps = conn.createStatement();
		res = ps.executeQuery(query);		
		return res;
	}

public void Insert(String nm)
	{
		try{
		PreparedStatement st;
		String query = "INSERT into studentregistration (names) VALUES (?)";
		DbConnection dbconn = new DbConnection();
		Connection conn = dbconn.dbConn();		
		st = conn.prepareStatement(query);			
		st.setString(1,nm);
		int rr = st.executeUpdate();
		System.out.println(rr);
		}catch(Exception e){e.printStackTrace();}
	}
}

SearchByName.java

public class SearchByName{
        ResultSet res;
	java.util.List<String> listName = new ArrayList<String>();
	JComboBox comboStudentNames = new JComboBox();
	CustomerLayout cl = new CustomerLayout();

public void loadStudents() throws ClassNotFoundException, SQLException
	  {
		listName = cl.saveStudent();
	    DefaultComboBoxModel model = new DefaultComboBoxModel();
	    ListIterator iter = listName.listIterator();
	    while (iter.hasNext())
	    {
	      model.addElement(((String)iter.next()));
	    }    
	    comboStudentNames.setModel(model);
	  }  

public SearchByName() throws SQLException, ClassNotFoundException
	{
		final Db db = new Db();
		res = db.NameValues();
		while(res.next())
		  {	  
			  listName.add(res.getString("names"));
		  }
	    loadStudents();
            coursePanel.add(comboStudentNames);                                          //adding to panel
}
}

(all are parts of my classes, not the whole class).
can you please tell me m i doing some mistake in distributing the code??
Thank you

[Michael Dunn]

if the problem of "how to auto update jcombobox?" is resolved, your next problem should be a separate topic.
that way you'll get more people looking at the problem, particularly if the subject is clearly defined.

also, you need to post a demo program of the problem, exactly like I posted - compilable/runnable, not snippets.
Like many here, I rarely read snippets (takes too much time). Strip everything unrelated to the problem.
if its nothing db related, simulate the db as an arraylist (as in my demo).
If the problem is db - it should be posted in the jdbc forum.

Basically, post a compilable/runnable demo, and tell us what it's supposed to do, what its actually doing,
and the steps to reproduce the problem

[Punit Jain]

actually i need to distribute your demo code into two classes one will display textbox and button and second will display the combo box..
i m trying like this:
Testing.java

import javax.swing.*;  
import java.awt.*;  
import java.awt.List;
import java.awt.event.*;  
import java.util.*;  
import javax.swing.*;  
import java.awt.*;  
import java.awt.List;
import java.awt.event.*;  
import java.util.*;  
class Testing  
{  
  java.util.List<String> database = new ArrayList<String>();  
  //JComboBox studentNames = new JComboBox();  
  JTextField tf = new JTextField();
  JFrame f = new JFrame();
  JPanel p = new JPanel(new GridLayout(3,1));
  SearchTesting st = new SearchTesting();
  public void buildGUI()  
  {  
    JButton btn = new JButton("Add New Student Name");  
    p.add(tf);
    p.add(btn);  
      
    f.getContentPane().add(p);  
    f.getContentPane().add(st);
    st.hide();
    f.pack();  
    f.setLocationRelativeTo(null);  
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);  
    f.setVisible(true);  
    btn.addActionListener(new ActionListener(){  
      public void actionPerformed(ActionEvent ae){  
        saveStudent(); 
        st.show();
        p.hide();
      }  
    });  
  }    
  public java.util.List<String> saveStudent()  
  {  
    database.add((String)(tf.getText()));//needs error handling  
    tf.setText("");  
    new SearchTesting().loadStudents();
    return database;
  }  
  public static void main(String[] args)  
  {  
    SwingUtilities.invokeLater(new Runnable(){  
      public void run(){  
        new Testing().buildGUI();  
      }  
    });  
  }  
}  

SearchTesting.java

import javax.swing.*;  
import java.awt.*;  
import java.awt.event.*;  
import java.util.*;  
class SearchTesting extends JPanel
{  
  java.util.List database1 = new ArrayList();  
  JComboBox studentNames = new JComboBox();
  Testing t = new Testing();
  
  public void buildGUI()  
  {  
    loadStudents();       
      
    this.add(studentNames);  
  }  
  public void loadStudents()  
  {
	  database1 = t.saveStudent();
    DefaultComboBoxModel model = new DefaultComboBoxModel();  
    ListIterator iter = database1.listIterator();  
    while (iter.hasNext())  
    {  
      model.addElement(((String)iter.next()));  
    }  
    studentNames.setModel(model);  
  }    
} 

but i m getting exception:

Exception in thread "AWT-EventQueue-0" java.lang.StackOverflowError
	at sun.awt.SunToolkit.isInstanceOf(Unknown Source)
	at sun.awt.SunToolkit.isInstanceOf(Unknown Source)
	at sun.awt.SunToolkit.isInstanceOf(Unknown Source)
	at sun.awt.SunToolkit.isInstanceOf(Unknown Source)
	at sun.awt.SunToolkit.isInstanceOf(Unknown Source)..............................................................................................

[Michael Dunn]

here's a very simple example of that error
run it, confirm same error, if so, work out why, then look for similarities in your code

class A
{
  public A()
  {
    B b = new B();
  }
  public static void main(String[] args){new A();}
}
class B
{
  public B()
  {
    A a = new A();
  }
}

[Punit Jain]

okay..
it's going to be an infinite loop..
because in class a i m calling class b and in class b i am calling class a..
no break condition..
it will continue until stack full.

[Punit Jain]

but how do i distribute it in two classes??
i tried it allot..
but many times there is no exceptions but second class combo is not updating.

[Punit Jain]

load student method is loading records into combobox.
save student is saving record of text field.
if want records to be loaded in another panel of other class.
and records which is going to be saved of the text field value is in another class.
so one class will have loadstudent method.
and other will have save student.
so in this case i have to create object of both class in each other.

[Michael Dunn]

you seem to have just copied bits and pieces and put them together in any fashion,
which will never work.

e.g. in the class SearchTesting, presumably you want the students loaded when the
program starts, but loadStudents() is in 'public void buildGUI()' - which is called by ??

There are so many errors in the way you've done it, that just fixing them is not going
to help you. You need to find them/understand them/fix them.

couple of options:
1)
print out the 2 classes you've created and after each line write what that line is to do,
or if a method line e.g. public void loadStudents(), what it is to do and/or return.

2)
start again, using my demo as a guide only. if you want a separate class to load the
students, create one. if you want a separate class to save a student, create one. The
class that displays it all (the frame etc), is a separate class to the other 2, so that's now
3 classes. You may need to pass references between the classes.

personally, (2) is the better option.

[Punit Jain]

okay..
i tried to do with the second option, but getting one exception.

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
	at javax.swing.JComboBox.setModel(Unknown Source)
	at load.Display$1.actionPerformed(Display.java:37)
	at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)

i m doing something like this:
Display.java

package load;

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.ArrayList;
import javax.swing.*;
public class Display{	
	JPanel panel, panel1;
	JTextField tf;	
	java.util.List<String> database = new ArrayList<String>();
    JButton btn; 
	JComboBox studentNames = new JComboBox();
	JFrame frame;
	DefaultComboBoxModel dcm = new DefaultComboBoxModel();
	LoadStudents ls = new LoadStudents();
	SaveStudent ss = new SaveStudent();
	public Display() {
		btn = new JButton("Add Student");
		tf = new JTextField(15);		
		panel = new JPanel();
		panel1 = new JPanel();
		panel.add(tf);
		panel.add(btn);		
		frame = new JFrame();
		frame.add(panel);
		frame.setVisible(true);
		frame.setSize(200,100);
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		btn.addActionListener(new ActionListener() {		
			public void actionPerformed(ActionEvent arg0) {
				String values = tf.getText();
				ss.saveStudent(values);
				panel.hide();
				panel.repaint();
				panel.revalidate();
				dcm = ls.ld();
				studentNames.setModel(dcm);
				panel1.add(studentNames);
				frame.add(panel1);								
			}
		});
	}	 
	 public static void main(String args[]){
		 new Display();	
	 }
}

SaveStudent.java

package load;

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.ArrayList;
import javax.swing.*;
public class SaveStudent{
	ArrayList<String> database = new ArrayList<String>();
	
	public void saveStudent(String values)  
	  {
		LoadStudents ls = new LoadStudents();
	    database.add(values);  	      
	    ls.loadStudents1(database);	    
	  }	
}

LoadStudents.java

package load;
import java.util.ArrayList;
import java.util.ListIterator;
import javax.swing.*;

public class LoadStudents {	
	ArrayList<String> database1;  
	DefaultComboBoxModel model;
	public void loadStudents1(ArrayList<String> al)  
	  {  
		database1 = al;
		System.out.println(database1);
	    model = new DefaultComboBoxModel();  
	    ListIterator iter = database1.listIterator();  
	    while (iter.hasNext())  
	    {  System.out.println(model);
	      model.addElement(((String)iter.next()));  
	    }  	   	     
	  }  
	public DefaultComboBoxModel ld()
	{		
		return model;
	}
}

can i do like this:

public DefaultComboBoxModel ld()
	{		
		return model;
	}

i mean this block is returning null value, therefore the exception is.
but don't know how to solve it.

[Rob Spoor]

You declare a LoadStudents object in line 15. You use this object to get the DefaultComboBoxModel in line 36. In between you never call its loadStudents1 method. That's why the DefaultComboBoxModel remains null.
You do call loadStudents1 inside class SaveStudent, but that uses a completely different LoadStudents object. The two are not related, and calling loadStudents1 on one will not set the model of the other.

[Punit Jain]

you mean i need to pass the reference also..??

[Michael Dunn]

> you mean i need to pass the reference also..??

but not between LoadStudents and SaveStudent - they (should) know nothing about each other.
I had it that way in the demo, when they were just methods in a single class, but it won't
work that same way when in separate classes (it can, but it gets messy)

you need to pass a reference of the comboBox to LoadStudents (via the LoadStudents constructor),
so that after all students are added to the model, the model is set as the comboBox model.

you have at line 32
ss.saveStudent(values);//you need to also pass a reference of the 'database' in the SaveStudent constructor, not create a separate 'database'
have, at line 33
ls.loadStudents1();//the 'database' reference should be part of the LoadStudents constructor

[Punit Jain]

thank you very very much...
it's working now..
but i have a question..
i need to connect it with database..
that time also i need arraylist??
flow would be same that time also??
i mean i m persisting value into database and then fetching again from database, why arraylist is required there??

[Michael Dunn]

the arraylist was used to simulate a resultset from a database.

you could probably still use an ArryList, if you wanted to create a db connector class.

just remember to have your db queries in a separate thread, or SwingWorker, so you don't lock up the GUI

[Punit Jain]

thank you michael, i have done some modifications.
but it's not updating again..
sorry but i am again doing mistake somewhere..
here is my two classes (save student and load student)..

public class SaveStudent{
	public void saveStudent(String values, ArrayList<String> aa) throws SQLException  
	  {		
		Db db = new Db();		
		LoadStudents ls = new LoadStudents();
	    aa.add(values);  
	    db.Insert1(values);
	    ls.loadStudents1(aa);	    
	  }	
}

public class LoadStudents {	
	ArrayList<String> database1;  
	DefaultComboBoxModel model;
	public void loadStudents1(ArrayList<String> al) throws SQLException  
	  {  
		ResultSet res;
		database1 = al;
		Db db = new Db();
		System.out.println(database1);
	    model = new DefaultComboBoxModel();  
	    ListIterator iter = database1.listIterator();
	    res = db.NameValues();
	    while(res.next()){
	      System.out.println(model);
	      model.addElement((res.getString("names")));
	    }
	    }  	   	     	  
	public DefaultComboBoxModel ld()
	{		
		return model;
	}
}

i also tried without arraylist, but it was again not working.
and also while fetching records in jcombobox, i am not using arraylist anywhere, is this the mistake, but don't know where to use..

Insert1(): method to insert value into database.
NameValues(): method to fetch data.

[Michael Dunn]

I don't see any comboBox in that code - the part where you set the model

[Punit Jain]

here is that code..

studentName = new JComboBox();
		final Db db = new Db();		
		res = db.NameValues();			
		//dcbm = ls.ld(); 
		while(res.next()){
			dcbm.addElement(res.getString("names"));			
		}			
		studentName.setModel(dcbm);

whenever i am uncommenting this line
//dcbm = ls.ld();
it giving me null pointer exception...

[Michael Dunn]

I have no idea what you're doing in these latest snippets, the comboBox snippet
doesn't indicate what method it belongs in.

this
model.addElement((res.getString("names")));
changes to
dcbm.addElement(res.getString("names"));
so, is this another method? or same method with a name change - if so, why? - it's confusing

go back to where you had it working, then add the changes one line at a time.
if you need to change a line, comment it out, don't delete it, so you can see
the old replaced by the new.

perhaps, in the changes you've made, you've added things in the wrong order.

[Punit Jain]

dcbm.addElement(res.getString("names"));

it's comboboxmodel.
but here i am directly fetching data from database, no other method i am calling, i m getting confused.
i know it's annoying michael, but can i please post part of my classes to show you what i am doing..

[Michael Dunn]

if the only changes you've made are in SaveStudent and LoadStudents, just post those 2 classes.

[Punit Jain]

actually my saveStudent and loadStudent both are same to those i posted in my third last post, in this post:

thank you michael, i have done some modifications.
but it's not updating again..
sorry but i am again doing mistake somewhere..
here is my two classes (save student and load student)..

but i am doing some mistake when i m calling them..
below is the part of my registration class, i m posting the actionListener which i added to my button:

	public class Register implements ActionListener			// Inner Class
	{
		public void actionPerformed(ActionEvent e)	
		{
			if(e.getSource()==btnRegister)
			{
				try{
					Db db = new Db();
					String name = txtName.getText();
					System.out.println(name);
					ss.saveStudent(name, database);					
				}
				catch(Exception e1){
					e1.printStackTrace();
				}				
			}
		}		

below is the part of class, where i am loading values into combobox.

public class SearchByName
{
public SearchByName() throws SQLException, ClassNotFoundException
	{		
		DefaultComboBoxModel dcbm = new DefaultComboBoxModel();
		JComboBox studentName = new JComboBox();
		final Db db = new Db();		
		ResultSet res = db.NameValues();			
		//dcbm = ls.ld(); 
		while(res.next()){
			dcbm.addElement(res.getString("names"));			
		}			
		studentName.setModel(dcbm);
                JPanel coursePanel = new JPanel();
		coursePanel.add(studentName);
	}
}

i m posting those part of class, which is related to this.
and below is my two methods of Db class.

public class Db
{
public ResultSet NameValues() throws SQLException{
		Statement ps;
		ResultSet res;
		System.out.println("Inside db");
		String query  = "SELECT names FROM studentregistration";
		DbConnection dbconn = new DbConnection();
		Connection conn = dbconn.dbConn();		
		ps = conn.createStatement();
		res = ps.executeQuery(query);		
		return res;
	}

public void Insert1(String nm)
	{
		try{
		PreparedStatement st;
		String query = "INSERT into studentregistration (names) VALUES (?)";
		DbConnection dbconn = new DbConnection();
		Connection conn = dbconn.dbConn();		
		st = conn.prepareStatement(query);			
		st.setString(1,nm);
		int rr = st.executeUpdate();
		System.out.println(rr);
		}catch(Exception e){e.printStackTrace();}
	}
}

DbConnection class has the database connection only..

[Michael Dunn]

in SearchByName you create a new comboBox
JComboBox studentName = new JComboBox();

you create a new JPanel
JPanel coursePanel = new JPanel();

you add the comboBox to the panel
coursePanel.add(studentName);

now what do you do with it?

[Punit Jain]

in my SearchByName class i have to take a argument, DefaultComboBoxModel and set that into JComboBox, but if i pass a argument(DefaultComboBox) to the constructor of SearchByName class, that where i am creating instance of that class, i have to pass a DefaultComboBoxModel.

so i tried like this: i created one method in my class SearchByName (say, Display()), that we earlier have in the Display1 class, and in this method i did all the work which i was doing in constructor of SearchByNameClass.

public void Display(DefaultComboBoxModel dcm) throws SQLException{
		 
		studentName = new JComboBox();
		dcbm = dcm;
		final Db db = new Db();		
		res = db.NameValues();			
		//dcbm = ls.ld(); 
		while(res.next()){
			dcbm.addElement(res.getString("names"));			
		}					
               studentName.setModel(dcbm);
	}

and i called this method in my Register class which implementing the ActionListener, but not working.

[Michael Dunn]

it seems you've brewed up some spaghetti code - it's all over the place

here's a breakdown of what should be where (I've removed the ArrayList stuff, add it back later if you really need it)

this assumes the Button's actionListener class (Register) can 'see' an instance of SaveStudent() and LoadStudents()

public class Db// this seems OK
//======================================
public void Display(DefaultComboBoxModel dcm) throws SQLException{
//this method is just repeating other code - get rid of it, or don't call it - delete later
//======================================
public class Register implements ActionListener
{
  String name = txtName.getText();
  //ss.saveStudent(name, database); //the db is already in the SaveStudent() class 
  ss.saveStudent(name); 
  [LoadStudents() reference].loadStudents1(comboBox reference);//this is where you load the students
}
//======================================

public class SearchByName
{
  //this class needs to be scrapped, but you need to add the panel/combo elsewhere in the program
  JComboBox studentName = new JComboBox(); 
  JPanel coursePanel = new JPanel();  
  coursePanel.add(studentName);  
}
//======================================

public class SaveStudent{//save the student name only.
  //public void saveStudent(String values, ArrayList<String> aa) throws SQLException 
  public void saveStudent(String values) throws SQLException 
  {   
    Db db = new Db();   
    //LoadStudents ls = new LoadStudents();
    //aa.add(values);  
    db.Insert1(values);
    //ls.loadStudents1(aa);     
  } 
}
//======================================

public class LoadStudents { 
  //ArrayList<String> database1;  
  //DefaultComboBoxModel model;
  //public void loadStudents1(ArrayList<String> al) throws SQLException  
  public void loadStudents1(JComboBox cbo) throws SQLException  
  {  
    //ResultSet res;
    //database1 = al;
    Db db = new Db();
    DefaultComboBoxModel model = new DefaultComboBoxModel();  
    //ListIterator iter = database1.listIterator();
    ResultSet res = db.NameValues();
    while(res.next()){
      //System.out.println(model);
      model.addElement((res.getString("names")));
    }
    cbo.setModel(model);
  }               
  //public DefaultComboBoxModel ld()
  //{   
    //return model;
  //}
}

[Punit Jain]

[LoadStudents() reference].loadStudents1(comboBox reference);//this is where you load the students

you mean by, this will come in my SearchByName class, because i am loading my combobox there, so instead of Register class i put this into my SearchByName class, like this:

public class SearchByName  
{  
  //this class needs to be scrapped, but you need to add the panel/combo elsewhere in the program  
  ls.loadStudents1(studentNames);
  JComboBox studentName = new JComboBox();   
  JPanel coursePanel = new JPanel();    
  coursePanel.add(studentName);    
}  

others i did in the same manner as you said, but again not updating..
don't know what's going wrong...

[Michael Dunn]

this is my comment from last post
//======================================
public class SearchByName
{
//this class needs to be scrapped, but you need to add the panel/combo elsewhere in the program
JComboBox studentName = new JComboBox();
JPanel coursePanel = new JPanel();
coursePanel.add(studentName);
}
//======================================

so, at this stage scrap the class (add the panel/comboBox to the gui some other way).
The name of the class indicates this is additional functionality you're trying to build in.
If so, do that later. Just get the progarm working where:
1) type a name into the textfield
2) click a button
3) the typed-in name is saved to the db
4) the newly saved name appears in the comboBox (indicating it has been saved to the db)

when you have the above working, add your code to search.

[Punit Jain]

actually SearchByName is the class where my JComboBox is in which data is coming from the database, and based on combobox selected value, related data is filled into the textfields, which are also in the same class.

1) type a name into the textfield
2) click a button
3) the typed-in name is saved to the db
4) the newly saved name appears in the comboBox (indicating it has been saved to the db)

this all is working fine, my data is saved into db, and also it appears into the combobox, but for that i have to restart my application.
newly saved name is appears after restarting my application.

[Michael Dunn]

> newly saved name is appears after restarting my application.

then something is wrong in LoadStudents - are you sure you're loading them
into the comboBox on the screen, not just loading them into a new comboBox?

[Punit Jain]

yes i m loading that.

view plaincopy to clipboardprint?
public class SearchByName
{
//this class needs to be scrapped, but you need to add the panel/combo elsewhere in the program
ls.loadStudents1(studentNames); // here i am loading it.---------------------------------->
JComboBox studentName = new JComboBox();
JPanel coursePanel = new JPanel();
coursePanel.add(studentName);
}

[Punit Jain]

i also tried by returning the comboboxmodel, from my loadstudent1() method, and setting this comboboxmodel to combobox in SearchByName class.
but again the problem is still remains.

[Michael Dunn]

as long as you continue using the SearchByName class, you will have problems.

post back when you've modified your code to remove that class.

[Punit Jain]

okay i removed all the code from my four classes in which i m implementing this.
CustomerLayout.java

public class CustomerLayout extends JPanel
{
	JPanel panel, btnPanel;
	JLabel lblName; 
	JTextField  txtName;
	JButton btnRegister;
	GridBagLayout gbLayout;
	GridBagConstraints gbc;
	Register rr;
	Db d;
	LoadStudents ls = new LoadStudents();
	SaveStudent ss = new SaveStudent();
	ArrayList<String> listNames = new ArrayList<String>();
	ArrayList<String> database = new ArrayList<String>();  
	DefaultComboBoxModel dcm = new DefaultComboBoxModel();
	JComboBox studentNames = new JComboBox();

	public CustomerLayout() throws SQLException
	{
		gbLayout = new GridBagLayout();	
		gbc = new GridBagConstraints();
		panel = new JPanel();
		panel.setLayout(gbLayout);
		lblName = new JLabel("Name");
		txtName = new JTextField(14);
		btnRegister = new JButton("Register");
	
		/*label name*/
		gbc.gridx = 4;
		gbc.gridy = 0;
		gbLayout.setConstraints(lblName,gbc);
		panel.add(lblName);
		
		/*text name*/
		gbc.gridx = 5;
		gbc.gridy = 0;	
		gbLayout.setConstraints(txtName,gbc);
		panel.add(txtName);
		
		/*Button Register*/
		rr = new Register();
		btnPanel = new JPanel();
		btnPanel.add(btnRegister);
		gbc.gridx = 1;
		gbc.gridy = 9;
		gbc.ipady = 0;
		gbc.weighty = 0.8;			
		panel.add(btnPanel,gbc);		
		btnPanel.add(btnRegister);			
		btnRegister.addActionListener(rr);
		panel.setBorder(new MatteBorder(5, 5, 30, 30, Color.lightGray));								
	}	
	
	public class Register implements ActionListener			// Inner Class
	{
		public void actionPerformed(ActionEvent e)	
		{
			if(e.getSource()==btnRegister)
			{
				try{
					String name = txtName.getText();
					System.out.println(name);
					ss.saveStudent(name);		
				}
				catch(Exception e1){				
					e1.printStackTrace();
				}				
			}
		}
		
	}	 
}

SearchByName.java

public class SearchByName extends JPanel
{
	JPanel panel;
	GridBagLayout gbLayout;
	GridBagConstraints gbc;
	LoadStudents ls = new LoadStudents();
	DefaultComboBoxModel dcbm= new DefaultComboBoxModel();
	JComboBox studentNames = new JComboBox();	
	public SearchByName() throws SQLException, ClassNotFoundException
	{		
		ls.loadStudents1(studentNames);		
		gbLayout = new GridBagLayout();	
		gbc = new GridBagConstraints();
		panel = new JPanel();
		panel.setLayout(gbLayout);														
		panel.add(studentNames);		
		panel.setBorder(new MatteBorder(5, 5, 30, 30, Color.lightGray));					
	}		
	}

LoadStudents.java

public class LoadStudents {	
	ArrayList<String> database1;  
	DefaultComboBoxModel model;	
	public void loadStudents1(JComboBox cbo) throws SQLException  
	  {
		ResultSet ress;
		Db db = new Db();
	    model = new DefaultComboBoxModel();  
	    ress = db.NameValues();
	    while(ress.next()){
	        model.addElement(ress.getString("names"));  
	  }cbo.setModel(model);
	  }  
}

SaveStudent.java

public class SaveStudent{	
	public void saveStudent(String values) throws SQLException  
	  {
		Db db = new Db();
	    db.Insert1(values);	   	   
	  }	
}

the db class i have posted earlier.
apart from these five class(including db), i have one main class in which i m hiding and showing these panels, on some event.

[Punit Jain]

post back when you've modified your code to remove that class.

i can't remove that class, that class has my search form.
and i have to load that combobox into that class.

[Michael Dunn]

sorry, can't do anything more when only half-classes are posted
e.g. in CustomerLayout() everything is added to 'JPanel panel', but what is
'panel' added to? - nothing, so it can't possibly have displayed anything.

this is getting very similar to one of your other topics, it just goes around in circles