title: Get selected JComboBox value and add to SQL query for second JComboBox
body: <p>I am designing a simple database application that features 2 jComboBoxes in the GUI. The first jComboBox is populated with the results of an SQL query. I would like the second jComboBox to populate with the results of a second query that incorporates the user selected value in the first box, but I can't quite get it to work.</p>
  
  <p>I have created 2 classes, one that draws the GUI and contains the main method, and a second class that queries my Oracle database. </p>
  
  <p>My GUI class:</p>
  
  <pre><code>public class TestUI extends javax.swing.JFrame {
       // Create new form TestUI
      public TestUI() {
          initComponents();
      }
  
      @SuppressWarnings("unchecked")
  
      private void initComponents() {
  
          jPanel1 = new javax.swing.JPanel();
          jComboBox1 = new javax.swing.JComboBox&lt;&gt;();
          jTextField1 = new javax.swing.JTextField();
          jComboBox2 = new javax.swing.JComboBox&lt;&gt;();
          jButton1 = new javax.swing.JButton();
          jButton2 = new javax.swing.JButton();
          setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
  
          // Combo box 1 population
  
          jComboBox1.removeAllItems();
          createConnection c1 = new createConnection();
          c1.getEmployee().forEach((employee) -&gt; {
              jComboBox1.addItem(employee);
          });
          jComboBox1.addActionListener(new java.awt.event.ActionListener() {
              public void actionPerformed(java.awt.event.ActionEvent evt) {
                  jComboBox1ActionPerformed(evt);
              }
          });
  
          // ComboBox 2 population
  
          jComboBox2.removeAllItems();
  
  
      }                     
  
      private void jComboBox1ActionPerformed(java.awt.event.ActionEvent evt) {                                           
          // TODO add handling code here:
      }                                    
  
      public static void main(String args[]) {
          DRAW GUI
      }
  }
  </code></pre>
  
  <p>And my database class:</p>
  
  <pre><code>import java.util.List;
  import java.util.ArrayList;
  import java.sql.*;
  
  public class createConnection {
  
      String empName;
  
      public Connection createConnection() {
          try {
              Class.forName(driver);
              java.sql.Connection conn = DriverManager.getConnection(DB_URL, DB_username, DB_password);
              return conn;
          } catch (ClassNotFoundException | SQLException e) {
              return null;
          }
      }
  
      // ComboBox 1
      public List&lt;String&gt; getEmployee() {
          List&lt;String&gt; list = new ArrayList();
          Connection conn = createConnection();
          try {
              Statement stmt = conn.createStatement();
              String query = "SELECT * FROM hr.employees ORDER BY last_name";
              ResultSet results = stmt.executeQuery(query);
              while (results.next()) {
                  list.add(results.getString("last_name"));
              }
          } catch (Exception e) {
              System.out.println("Exception = " + e);
          }
          return list;
      }
  
      // Combo Box 2
      public List&lt;String&gt; getEmpLocation() {
          List&lt;String&gt; list = new ArrayList();
          Connection conn = createConnection();
          try {
              Statement stmt = conn.createStatement();
              String query = "SELECT country_id FROM hr.location WHERE hr.location.emp_name = " + empName;
              ResultSet results = stmt.executeQuery(query);
              while (results.next()) {
                  list.add(results.getString("last_name"));
              }
          } catch (Exception e) {
              System.out.println("Exception = " + e);
          }
          return list;
      }    
  }
  </code></pre>
  
  <p>I have left out irrelevant code like db connection variables and GUI coordinates etc.</p>
  
  <p>I am wondering how to properly get the getEmpLocation() method in the database class to populate the 2nd ComboBox. This will involve adding code to both classes and passing the variable value but I can't figure it out! Any help would be greatly appreciated here.</p>