Why can't I get KeyEvent.VK_TAB when I use Key Binding for a JPanel

Question

I will print related info if users focus on current window and press a key. However, it works for some keys like \'a\' but not for \'tab\'. Here is a simple demo:

Answer 1

• interesting issue with TAB, looks like as bug, because isn't possible to get, capture the KeyChar from TAB without using Shift_TAB before, event from TAB is somehow consumed elsewhere, no idea whats happened

• my view - there is an issue with Focus because key TAB is used by Native OS and as built_in KeyBindings in Swing,

• opposite issue with TAB and Shift_TAB in question Java Swing: how to stop unwanted shift-tab keystroke action

• maybe someone has explanation how to catch a TAB event

• TAB is used as KeyBindings (built_in in API) for many JComponents or navigations inside Container contains more than one JComponent

funny output from AWTEventListener (win8_64b/Java7_xxx)

     is typed //tab is pressed
     is typed
     is typed
     is typed
     is typed
     is typed
     is typed
     is typed
     is typed
 is typed //shift is pressed
 is typed
 is typed
 is typed
 is typed
 is typed
 is typed
 is typed
 is typed
 is typed
 is typed
 is typed
 is typed
 is typed
 is typed
 is typed
 is typed
 is typed
 is typed
 is typed
 is typed
 is typed
 is typed
 is typed
 is typed
 is typed
 is typed
 is typed
 is typed
     is typed // tab is pressed again
     is typed
     is typed
     is typed
 is typed //:-) nobody knows something from milky way
 is typed
     is typed
shift tab is typed //now is tab event unlocked for Container in Swing
shift tab is typed
shift tab is typed
ctrl tab is typed
ctrl tab is typed
ctrl tab is typed
tab is typed // now is possible, finally TAB is unlocked and firing an event
tab is typed
tab is typed

from code

import java.awt.AWTEvent;
import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.Toolkit;
import java.awt.event.AWTEventListener;
import java.awt.event.ActionEvent;
import java.awt.event.KeyEvent;

import javax.swing.AbstractAction;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.KeyStroke;

//https://stackoverflow.com/q/24800417/714968
public class KeyBindingTest {

    public static void main(String[] args) {
        KeyBindingTest test = new KeyBindingTest();
        test.createUI();
    }

    public void createUI() {
        JFrame frame = new JFrame("KeyBinding Test");
        MainPanel mainPanel = new MainPanel();
        frame.add(mainPanel, BorderLayout.CENTER);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
        Toolkit.getDefaultToolkit().addAWTEventListener(new AWTEventListener() {
            @Override
            public void eventDispatched(AWTEvent event) {
                if (event instanceof KeyEvent) {
                    KeyEvent ke = (KeyEvent) event;
                    System.out.println(ke.getKeyChar() + " is typed");
                }
            }
        }, AWTEvent.KEY_EVENT_MASK);
    }

    @SuppressWarnings("serial")
    class MainPanel extends JPanel {

        public MainPanel() {
            setPreferredSize(new Dimension(200, 200));
            //========================key binding============================
            //requestFocusInWindow();
            String aString = "aStr";

            getInputMap().put(KeyStroke.getKeyStroke(KeyEvent.VK_A, 0), aString);
            getActionMap().put(aString, new AbstractAction() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    // TODO Auto-generated method stub
                    System.out.println("a is typed");
                }
            });
            String tabString = "TAB";
            this.getInputMap(JComponent.WHEN_IN_FOCUSED_WINDOW).put(KeyStroke.getKeyStroke(tabString), tabString);
            //getInputMap().put(KeyStroke.getKeyStroke(KeyEvent.VK_TAB, 0), tabString);
            this.getActionMap().put(tabString, new AbstractAction() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    // TODO Auto-generated method stub
                    System.out.println("tab is typed");
                }
            });
            String tabShiftString = "shift TAB";
            this.getInputMap(JComponent.WHEN_IN_FOCUSED_WINDOW).put(KeyStroke.getKeyStroke(tabShiftString), tabShiftString);
            //getInputMap().put(KeyStroke.getKeyStroke(KeyEvent.VK_TAB, 0), tabString);
            this.getActionMap().put(tabShiftString, new AbstractAction() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    // TODO Auto-generated method stub
                    System.out.println("shift tab is typed");
                }
            });
            String ctrlShiftString = "ctrl TAB";
            this.getInputMap(JComponent.WHEN_IN_FOCUSED_WINDOW).put(KeyStroke.getKeyStroke(ctrlShiftString), ctrlShiftString);
            //getInputMap().put(KeyStroke.getKeyStroke(KeyEvent.VK_TAB, 0), tabString);
            this.getActionMap().put(ctrlShiftString, new AbstractAction() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    // TODO Auto-generated method stub
                    System.out.println("ctrl tab is typed");
                }
            });
        }
    }
}