MyPanel.java

import java.util.*;
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;

public class MyPanel extends JPanel implements KeyListener {
    private char c = 'e';

    public MyPanel() {
        this.setPreferredSize(new Dimension(500, 500));
        addKeyListener(this);
    }

    public void addNotify() {
        super.addNotify();
        requestFocus();
    }

    public void paintComponent(Graphics g) {
        g.clearRect(0, 0, getWidth(), getHeight());
        g.drawString("the key that pressed is " + c, 250, 250);
    }

    public void keyPressed(KeyEvent e) { }
    public void keyReleased(KeyEvent e) { }
    public void keyTyped(KeyEvent e) {
        c = e.getKeyChar();
        repaint();
    }

    public static void main(String[] s) {
        JFrame f = new JFrame();
        f.getContentPane().add(new MyPanel());
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.pack();
        f.setVisible(true);
    }
}