Java by API/javax.swing/DefaultComboBoxModel

new DefaultComboBoxModel(Object obj)

import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.DefaultComboBoxModel;
import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
public class MainClass {
  public static void main(final String args[]) {
    final String labels[] = { "A", "B", "C", "D", "E" };
    final DefaultComboBoxModel model = new DefaultComboBoxModel(labels);
    JFrame frame = new JFrame("Shared Data");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    JComboBox comboBox1 = new JComboBox(model);
    comboBox1.setMaximumRowCount(5);
    comboBox1.setEditable(true);
    frame.add(comboBox1, BorderLayout.NORTH);
    
    JList jlist = new JList(model);
    JScrollPane scrollPane = new JScrollPane(jlist);
    frame.add(scrollPane, BorderLayout.CENTER);
    JButton button = new JButton("Add");
    frame.add(button, BorderLayout.SOUTH);
    ActionListener actionListener = new ActionListener() {
      public void actionPerformed(ActionEvent actionEvent) {
        model.addElement("a");
      }
    };
    button.addActionListener(actionListener);

    frame.setSize(300, 200);
    frame.setVisible(true);
  }
}