create JTextField with keyboard event to show the popup window on key realeased,
Example:
jTextField2.addKeyListener(new java.awt.event.KeyAdapter() {
public void keyReleased(java.awt.event.KeyEvent evt) {
showPopup(evt);
}
});
void showPopup(java.awt.event.KeyEvent evt) {
JPopupMenu popup = new JPopupMenu();
popup.setLightWeightPopupEnabled(false);
popup.setBorder(BorderFactory.createLineBorder(Color.black));
popup.setLayout(new BorderLayout());
popup.setSize(this.getPreferredSize());
popup.setPreferredSize(this.getPreferredSize());
popup.pack();
popup.setOpaque(false);
// create panel that contains the search result
popup.add(BorderLayout.CENTER, <YOUR PANEL WITH THE RESULT>);
popup.setPreferredSize(new Dimension(jTextField2.getWidth(),250));
<SEARCH PANEL>.setPreferredSize(new Dimension(jTextField2.getWidth(),250));
popup.show(jTextField2, 0, jTextField2.getHeight());
}