<--- KLASA PANELU --->

import java.awt.Dimension;
import java.awt.event.KeyListener;
import java.awt.event.KeyEvent;
import javax.swing.JPanel;
import java.awt.Color;

public class KeyPanel extends JPanel implements KeyListener{

    public KeyPanel(){
    addKeyListener(this);
    setPreferredSize(new Dimension(300, 100));
    }

    @Override
    public void keyPressed(KeyEvent e){
    setBackground(Color.YELLOW);
    }

    @Override
    public void keyReleased(KeyEvent e){

    }

    @Override
    public void keyTyped(KeyEvent e){

    }
}

<--- KLASA RAMKI --->

import javax.swing.JFrame;
import javax.swing.JPanel;

public class KeyFrame extends JFrame{
    public KeyFrame(){
    super("Program okienkowy - zdarzenia Klawiatura");
    JPanel panel = new KeyPanel();
    add(panel);
    setVisible(true);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    pack();
    }
}

<--- KLASA TWORZĄCA RAMKĘ --->

import java.awt.EventQueue;

public class Test{
    public static void main(String[] args){
    EventQueue.invokeLater(new Runnable(){
            @Override
        public void run(){
            new KeyFrame();
            }
        });
    }
}