How can we implement auto-complete JComboBox in Java?\\n

A JComboBox is a subclass of JComponent class and it is a combination of a text field and a drop-down list from which the user can choose a value. A JComboBox can generate an ActionListener, ChangeListener, and ItemListener interfaces when the user actions on a combo box.

We can implement auto-complete JComboBox when the user types an input value from a keyboard by using customization of a combo box (AutoCompleteComboBox) by extending the JComboBox class.

Example

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.plaf.basic.*;
public class AutoCompleteComboBoxTest extends JFrame {
   private JComboBox comboBox;
   public AutoCompleteComboBoxTest() {
      setTitle("AutoCompleteComboBox");
      String[] countries = new String[] {"india", "australia", "newzealand", "england", "germany",
"france", "ireland", "southafrica", "bangladesh", "holland", "america"};
      comboBox = new AutoCompleteComboBox(countries);
      add(comboBox, BorderLayout.NORTH);
      setSize(400, 300);
      setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      setLocationRelativeTo(null);
      setVisible(true);
   }
   public static void main(String []args) {
      new AutoCompleteComboBoxTest();
   }
}
 // Implementtion of AutoCompleteComboBox
class AutoCompleteComboBox extends JComboBox {
   public int caretPos = 0;
   public JTextField tfield = null;
   public AutoCompleteComboBox(final Object countries[]) {
      super(countries);
      setEditor(new BasicComboBoxEditor());
      setEditable(true);
   }
   public void setSelectedIndex(int index) {
      super.setSelectedIndex(index);
      tfield.setText(getItemAt(index).toString());
      tfield.setSelectionEnd(caretPos + tfield.getText().length());
      tfield.moveCaretPosition(caretPos);
   }
   public void setEditor(ComboBoxEditor editor) {
      super.setEditor(editor);
      if(editor.getEditorComponent() instanceof JTextField) {
         tfield = (JTextField) editor.getEditorComponent();
         tfield.addKeyListener(new KeyAdapter() {
            public void keyReleased(KeyEvent ke) {
               char key = ke.getKeyChar();
               if (!(Character.isLetterOrDigit(key) || Character.isSpaceChar(key) )) return;
               caretPos = tfield.getCaretPosition();
               String text="";
               try {
                  text = tfield.getText(0, caretPos);
               } catch (javax.swing.text.BadLocationException e) {
                  e.printStackTrace();
               }
               for (int i=0; i < getItemCount(); i++) {
                  String element = (String) getItemAt(i);
                  if (element.startsWith(text)) {
                     setSelectedIndex(i);
                     return;
                  }
               }
            }
         });
      }
   }
}

Output