populate JcomboBox from MSAccess Database in java - jcombobox

Question

I'm new in using JComboBox, I wanted to populate JComboBox from my MSAccess Database. I have the following codes:
public check_Writer() //Constructor
{
gui();
fillCombo();
}
public void gui()
{
JFrame mainFrame = new JFrame("Frame");
mainFrame.setSize(500,500);
mainFrame.setVisible(true);
JPanel mainPanel = new JPanel();
mainPanel.setBackground(color.BLUE);
mainFrame.add(mainPanel);
JComboBox listofSuppliersCombo = new JComboBox()
mainPanel.add(listofSuppliersCombo);
}
public void fillCombo()
{
String dataSourceName = "CheckWriterDB";
String db = "jdbc:odbc:" + dataSourceName;
try
{
Class.forName(sun.jdbc.odbc.JdbcOdbcDriver);
Connection conn = DriverManager.getConnection(db, "", "");
Statement st1 = conn.createStatement();
st1.execute("select Suppliers from SuppliersTable");
ResultSet rs1 = st1.getResultSet();
if (rs1!null)
{
while(rs1.next())
{
System.out.println(rs1.getString(1));
}
}
}
catch(Exception e)
{
JOptionPane.showMessageDialog(null, e)
}
}
}
I edited my codes sir, my code works just fine i can print my data in the console, but i can't populate my JComboBox, I tried this code, listOfSuppliersCombo.addItem(rs1.getString(1)); but error message(java.lang.NullPointerException). Is there something wrong with the way created my combo box above, thank you very much sir.

Answer 1

You have defined listofSuppliersCombo locally in gui function, in order to reference any object, in two different mehods, you need to declare it in upper scope.
Your code will work if you try like below:
JComboBox listofSuppliersCombo;
public void gui()
{
//Your Code
listofSuppliersCombo=new JComboBox();
//Your Code
}
public void fillCombo()
{
//Your Code
listofSuppliersCombo.addItem("Your Item");
//Your Code
}