import java.awt.BorderLayout;
import javax.swing.DefaultComboBoxModel;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JTextField;
public class Main {
public static void main(String[] args) {
JFrame frame = new JFrame();
String[] list = { "Hello 1", "Hello 2", "Hello 3", "Hello 4" };
DefaultComboBoxModel<String> model = new DefaultComboBoxModel<>(list);
JComboBox<String> comboBox = new JComboBox<>(model);
frame.add(comboBox, BorderLayout.NORTH);
final JTextField textField = new JTextField(30);
frame.add(textField, BorderLayout.SOUTH);
frame.add(new JLabel("Type something, then press enter", JLabel.CENTER));
textField.addActionListener(ae -> {
String text = textField.getText();
model.addElement(text);
comboBox.setSelectedItem(text);
textField.setText("");
});
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.pack();
frame.setVisible(true);
}
}