import java.awt.Container;
import java.awt.Dimension;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.util.Vector;
import javax.swing.BoxLayout;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.text.JTextComponent;

public class TestFrame extends JFrame {

    JComboBox jComboBox1 = new JComboBox();
    Vector<String> all_CB_Items = new Vector<String>();

    public TestFrame() {
        super("Тестовое окно");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        Container content = getContentPane();
        content.setLayout(new BoxLayout(content, BoxLayout.Y_AXIS));
        jComboBox1.setEditable(true);
        jComboBox1.setAlignmentX(LEFT_ALIGNMENT);
        content.add(jComboBox1);

        populateCB();
        final JTextComponent jtc = (JTextComponent) jComboBox1.getEditor().getEditorComponent();
        KeyListener kl = new KeyListener() {
            @Override
            public void keyTyped(KeyEvent e) {
                populateCB();
            }

            @Override
            public void keyPressed(KeyEvent e) {
            }

            @Override
            public void keyReleased(KeyEvent e) {
                final String text = jtc.getText();
                for (int i = 0; i < all_CB_Items.size(); i++) {
                    if (!all_CB_Items.get(i).contains(text)) {
                        jComboBox1.removeItem(all_CB_Items.get(i));
                    }
                }
                jComboBox1.showPopup();
            }
        };
        jtc.addKeyListener(kl);

        setPreferredSize(new Dimension(240, 130));
        pack();
        setLocationRelativeTo(null);
        setVisible(true);
    }

    private void populateCB() {
        jComboBox1.removeAllItems();
        jComboBox1.addItem("");
        jComboBox1.addItem("1");
        jComboBox1.addItem("12");
        jComboBox1.addItem("123");
        jComboBox1.addItem("1234");
        jComboBox1.addItem("12345");
        all_CB_Items.removeAllElements();
        all_CB_Items.add("");
        all_CB_Items.add("1");
        all_CB_Items.add("12");
        all_CB_Items.add("123");
        all_CB_Items.add("1234");
        all_CB_Items.add("12345");
    }

    public static void main(String[] args) {
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                JFrame.setDefaultLookAndFeelDecorated(true);
                new TestFrame();
            }
        });
    }
}