如何在MS Access中从数据库的jcombobox添加多个项目

Question

import java.sql.*;
import java.awt.*;

import javax.swing.*;

import java.awt.event.*;

class ComboExample {
 Connection con;
 Statement st;
 ResultSet rs;

ComboExample() {
    JFrame f = new JFrame();
    f.getContentPane().setLayout(null);
    final JComboBox combo = new JComboBox();
        try {
             String driver = "sun.jdbc.odbc.JdbcOdbcDriver";
             Class.forName(driver);
             String db = "jdbc:odbc:TTracking";
             con = DriverManager.getConnection(db);

             // Getting database info
             DatabaseMetaData meta = con.getMetaData();
             System.out.println("Server name: " +
meta.getDatabaseProductName());
             System.out.println("Server version: " +
meta.getDatabaseProductVersion());
             System.out.println("");

             System.out.println("Creating statement...");
              st = con.createStatement();
              String sql = "SELECT Trailer FROM TrailerLocationMaster";
              ResultSet rs = st.executeQuery(sql);
                    while (rs.next()) {
        String trailer = rs.getString("Trailer");
        combo.addItem(trailer);
        System.out.println(rs.getString("Trailer"));
        combo.setVisible(true);
        }
        }
         catch (Exception ex) {
            }

    combo.setBounds(20, 50, 150, 20);
    f.add(combo);
    f.setSize(400, 200);
    f.setVisible(true);

}






public static void main(String[] args) {
    ComboExample c = new ComboExample();
    }
}

The combo-box displays correctly, but only one item from the database table appears why is that? and how do I allow multiple items to be in jcombobox from database? Also why does it always complain with and advises suppress warnings?

Answer 1

Don't use a null layout and setBounds(...). Swing was designed to be used with layout managers.

There is no need for comboBox.setVisible(true) since Swing components (except for top level containers) are visible by default.

Also why does it always complain with and advises suppress warnings?

You haven't specified the type of data that will adding the to the model of the combo box. You are adding String data so you should be using:

JComboBox<String> combo = new JComboBox<String>();

Read up on Generics for more information.

how do I allow multiple items to be in jcombobox from database?

You don't do anything special. Your code looks reasonable since you have a while loop and you invoked the addItem(...) method.

If you only have one item, then I would guess your query only returns a single item. Your output should verify this. Add more data to your table.