Display dropdown for JComboBox use a Keystroke If the Selected Item Is Not Unique in Java

//w w  w.  j  av a  2  s . c o m

import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;

import javax.swing.JComboBox;

public class Main {
  public static void main(String[] argv) throws Exception {
    String[] items = { "A", "A", "B", "B", "C" };
    JComboBox cb = new JComboBox(items);

    // Create and register the key listener
    cb.addKeyListener(new MyKeyListener());

  }
}

class MyKeyListener extends KeyAdapter {
  public void keyPressed(KeyEvent evt) {
    JComboBox cb = (JComboBox) evt.getSource();

    int curIx = cb.getSelectedIndex();

    char ch = evt.getKeyChar();

    JComboBox.KeySelectionManager ksm = cb.getKeySelectionManager();
    if (ksm != null) {
      // Determine if another item has the same prefix
      int ix = ksm.selectionForKey(ch, cb.getModel());
      boolean noMatch = ix < 0;
      boolean uniqueItem = ix == curIx;

      // Display menu if no matching items or the if the selection is not unique
      if (noMatch || !uniqueItem) {
        cb.showPopup();
      }
    }
  }
}