A DESCRIPTION OF THE PROBLEM :
The alt_graph key is reported incorrectly. Results differ between java versions and input schemes, but are always incorrect.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Use the Keycode Listener example from here.
https://docs.oracle.com/javase/tutorial/uiswing/events/keylistener.html
https://docs.oracle.com/javase/tutorialJWS/samples/uiswing/KeyEventDemoProject\KeyEventDemo.jar

Press the alt_gr key. Combine it with other keys like arrow up.
Compare java 8 with with java 11 or 13. Switch the keyboard layout between us/german

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Alt graph key is reported as alt_graph_key and or mask.
ACTUAL -
Depending on the combination of java version and keyboard layout the alt_gr key will be reported as either:

Alt ( no graph) (java 8)
Alt+ Alt_graph (us)
Alt+Alt_graph + ctrl (german)

---------- BEGIN SOURCE ----------
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package events;

/*
* KeyEventDemo
*/

import java.awt.BorderLayout;
import java.awt.Container;
import java.awt.Dimension;
import java.awt.event.*;
import javax.swing.*;

public class KeyEventDemo extends JFrame
        implements KeyListener,
        ActionListener
{
    JTextArea displayArea;
    JTextField typingArea;
    static final String newline = System.getProperty("line.separator");
    
    public static void main(String[] args) {
        /* Use an appropriate Look and Feel */
        try {
            //UIManager.setLookAndFeel("com.sun.java.swing.plaf.windows.WindowsLookAndFeel");
            //UIManager.setLookAndFeel("com.sun.java.swing.plaf.gtk.GTKLookAndFeel");
            UIManager.setLookAndFeel("javax.swing.plaf.metal.MetalLookAndFeel");
        } catch (UnsupportedLookAndFeelException ex) {
            ex.printStackTrace();
        } catch (IllegalAccessException ex) {
            ex.printStackTrace();
        } catch (InstantiationException ex) {
            ex.printStackTrace();
        } catch (ClassNotFoundException ex) {
            ex.printStackTrace();
        }
        /* Turn off metal's use of bold fonts */
        UIManager.put("swing.boldMetal", Boolean.FALSE);
        
        //Schedule a job for event dispatch thread:
        //creating and showing this application's GUI.
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI();
            }
        });
    }
    
    /**
     * Create the GUI and show it. For thread safety,
     * this method should be invoked from the
     * event-dispatching thread.
     */
    private static void createAndShowGUI() {
        //Create and set up the window.
        KeyEventDemo frame = new KeyEventDemo("KeyEventDemo");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        
        //Set up the content pane.
        frame.addComponentsToPane();
        
        
        //Display the window.
        frame.pack();
        frame.setVisible(true);
    }
    
    private void addComponentsToPane() {
        
        JButton button = new JButton("Clear");
        button.addActionListener(this);
        
        typingArea = new JTextField(20);
        typingArea.addKeyListener(this);
        
        //Uncomment this if you wish to turn off focus
        //traversal. The focus subsystem consumes
        //focus traversal keys, such as Tab and Shift Tab.
        //If you uncomment the following line of code, this
        //disables focus traversal and the Tab events will
        //become available to the key event listener.
        //typingArea.setFocusTraversalKeysEnabled(false);
        
        displayArea = new JTextArea();
        displayArea.setEditable(false);
        JScrollPane scrollPane = new JScrollPane(displayArea);
        scrollPane.setPreferredSize(new Dimension(375, 125));
        
        getContentPane().add(typingArea, BorderLayout.PAGE_START);
        getContentPane().add(scrollPane, BorderLayout.CENTER);
        getContentPane().add(button, BorderLayout.PAGE_END);
    }
    
    public KeyEventDemo(String name) {
        super(name);
    }
    
    
    /** Handle the key typed event from the text field. */
    public void keyTyped(KeyEvent e) {
        displayInfo(e, "KEY TYPED: ");
    }
    
    /** Handle the key pressed event from the text field. */
    public void keyPressed(KeyEvent e) {
        displayInfo(e, "KEY PRESSED: ");
    }
    
    /** Handle the key released event from the text field. */
    public void keyReleased(KeyEvent e) {
        displayInfo(e, "KEY RELEASED: ");
    }
    
    /** Handle the button click. */
    public void actionPerformed(ActionEvent e) {
        //Clear the text components.
        displayArea.setText("");
        typingArea.setText("");
        
        //Return the focus to the typing area.
        typingArea.requestFocusInWindow();
    }
    
    /*
     * We have to jump through some hoops to avoid
     * trying to print non-printing characters
     * such as Shift. (Not only do they not print,
     * but if you put them in a String, the characters
     * afterward won't show up in the text area.)
     */
    private void displayInfo(KeyEvent e, String keyStatus){
        
        //You should only rely on the key char if the event
        //is a key typed event.
        int id = e.getID();
        String keyString;
        if (id == KeyEvent.KEY_TYPED) {
            char c = e.getKeyChar();
            keyString = "key character = '" + c + "'";
        } else {
            int keyCode = e.getKeyCode();
            keyString = "key code = " + keyCode
                    + " ("
                    + KeyEvent.getKeyText(keyCode)
                    + ")";
        }
        
        int modifiersEx = e.getModifiersEx();
        String modString = "extended modifiers = " + modifiersEx;
        String tmpString = KeyEvent.getModifiersExText(modifiersEx);
        if (tmpString.length() > 0) {
            modString += " (" + tmpString + ")";
        } else {
            modString += " (no extended modifiers)";
        }
        
        String actionString = "action key? ";
        if (e.isActionKey()) {
            actionString += "YES";
        } else {
            actionString += "NO";
        }
        
        String locationString = "key location: ";
        int location = e.getKeyLocation();
        if (location == KeyEvent.KEY_LOCATION_STANDARD) {
            locationString += "standard";
        } else if (location == KeyEvent.KEY_LOCATION_LEFT) {
            locationString += "left";
        } else if (location == KeyEvent.KEY_LOCATION_RIGHT) {
            locationString += "right";
        } else if (location == KeyEvent.KEY_LOCATION_NUMPAD) {
            locationString += "numpad";
        } else { // (location == KeyEvent.KEY_LOCATION_UNKNOWN)
            locationString += "unknown";
        }
        
        displayArea.append(keyStatus + newline
                + " " + keyString + newline
                + " " + modString + newline
                + " " + actionString + newline
                + " " + locationString + newline);
        displayArea.setCaretPosition(displayArea.getDocument().getLength());
    }
}

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Use InputEvent.CTRL_DOWN_MASK|InputEvent.ALT_DOWN_MASK |InputEvent.ALT_GRAPH_DOWN_MASK
AND also InputEvent.ALT_DOWN_MASK |InputEvent.ALT_GRAPH_DOWN_MASK instead of InputEvent.ALT_GRAPH_DOWN_MASK .. at least for Java 11-13

FREQUENCY : always