Styjun

I am trying to fetch some values from the MySQL database to JComboBox using ArrayList and DefaultComboBoxModel to avoid fetching duplicate values. Because JComboBox keeps filling the same values again and again to the JComboBox when I called the method to fetch values.

Currently, when the following code runs combo box is showing values like these,

sometext@24084,
sometext@716a1

Here is my code,

public static void loadAll(JComboBox comboBox) ClassNotFoundException ex) 
 
 Logger.getLogger(AllComboBoxMethod.class.getName()).log(Level.SEVERE, null, ex);
 
 

And Fetch Method,

int itemCount = combo.getItemCount(); 

for(int i = 1; i < itemCount; i++) 
 combo.removeItemAt(0); 


String sql = "SELECT * FROM combo_type";
dbConnection = DbConnection.getInstance();
con = dbConnection.getConnection();
stm = con.createStatement();
rst = stm.executeQuery(sql);

ArrayList<Combo> comboList = new ArrayList();
while(rst.next()) 
 comboList.add(new Combo(rst.getString(2)));

return comboList;

So what I'm doing wrong? Is this the only way to avoid fetching duplicate values? I tried comboBox.removeAllItems() earlier (before adding this code) and then fetch the values. But it gives me NullPointerException some times. So how can I fix this?

This

sometext@716a1

is the unique identifier/memory address of a concrete class instance.

You're seeing that because you haven't correctly overridden the

public String toString();

method, for the Combo class.

Also, DefaultComboBoxModel is a generic enabled class

DefaultComboBoxModel<E>

so why are you using a raw instance?

You should be dealing with

DefaultComboBoxModel<Combo>

instead. Which means you could do

for (final Combo combo : comboList) 
 dtm.addElement(combo);

Try with

public static void loadAll(final JComboBox comboBox) 
 try 
 final List<Combo> comboList = ComboBoxController.getComboType();
 final DefaultComboBoxModel dtm = (DefaultComboBoxModel) comboBox.getModel();

 dtm.removeAllItems();

 for (final Combo combo : comboList) 
 dtm.addElement(combo.getComboType());
 
 catch (final SQLException 

int itemCount = combo.getItemCount();

for (int i = itemCount - 1; i >= 0; i++) 
 combo.removeItemAt(0);