title: For what component should I add KeyListener?
body: <p>I have a GUI.</p>
  
  <p>This GUI class extends JFrame.</p>
  
  <p>In top of the screen there is a JLabel with some text.</p>
  
  <p>In the center of the screen there is a JPanel, and n x n JButtons were added to this JPanel.</p>
  
  <p>I need a KeyListener to react if I press a key.</p>
  
  <p>For what component (JFrame, JLabel, JPanel, JButtons) should I add the KeyListener to work my program normally?  </p>