KeyListener doesn't work in Java

Question

I don't know why KeyListener doesn't work. The program should close if the user press "Shift".

public class Main extends JFrame implements KeyListener{

    public static void main(String[] args){
        new Main();
    }

    public Main(){
        JFrame guiFrame = new JFrame();

        //make sure the program exits when the frame closes
        guiFrame.setDefaultCloseOperation(JFrame.DO_NOTHING_ON_CLOSE);
        guiFrame.setLayout(new FlowLayout());
        guiFrame.setTitle("");
        guiFrame.setExtendedState(JFrame.MAXIMIZED_BOTH); 
        guiFrame.setUndecorated(true);
        guiFrame.setAlwaysOnTop(true);
        guiFrame.getContentPane().setBackground(Color.black);


        JLabel jb1 = new JLabel("WER DAS LIEST IST BLÖD",JLabel.CENTER);
        jb1.setFont(new Font("Serif", Font.BOLD, 140));
        jb1.setForeground(Color.WHITE);
        jb1.setLocation((guiFrame.getWidth()-jb1.getWidth())/2,50);


        guiFrame.add(jb1);
        //This will center the JFrame in the middle of the screen
        guiFrame.setLocationRelativeTo(null);
        guiFrame.setVisible(true);
    }

    @Override
    public void keyPressed(KeyEvent e) {

    }

    @Override
    public void keyReleased(KeyEvent e) {
        if(e.getKeyCode() == KeyEvent.VK_SPACE){
            System.exit(0);
        }

    }

    @Override
    public void keyTyped(KeyEvent e) {
        // TODO Auto-generated method stub

    }
}

Answer 1

Just implementing the KeyListener interface is not enough - you need to add it to some component (in your case the JFrame ).

Try something like

guiFrame.addKeyListener(this);

See here for the API: http://docs.oracle.com/javase/8/docs/api/java/awt/Component.html#addKeyListener-java.awt.event.KeyListener-

And here for a the official tutorial: https://docs.oracle.com/javase/tutorial/uiswing/events/keylistener.html