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


public class KeyListenerTest extends JFrame {
    JPanel contentPane = new JPanel();


    public void reNew(String addText){

        contentPane.add(new JLabel(addText));
    }


    KeyListenerTest() {
        super("Cat Dog Mouse Game");
        contentPane.setLayout(new GridLayout());

        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setContentPane(contentPane);

        contentPane.addKeyListener(new MyKeyListener());
        contentPane.requestFocus();
        setSize(0, 0);
        setVisible(true);
        contentPane.requestFocus();
    }

    class MyKeyListener extends KeyAdapter {
        public void keyPressed(KeyEvent e) {

            int keyCode = e.getKeyCode();
            switch (keyCode) {
                case KeyEvent.VK_UP:
                case KeyEvent.VK_W:
                    CatDogMouse.KEYINPUT = 'N';
                    //System.out.print("N");
                    break;
                case KeyEvent.VK_DOWN:
                case KeyEvent.VK_S:
                    CatDogMouse.KEYINPUT = 'S';
                    //System.out.print("S");
                    break;
                case KeyEvent.VK_LEFT:
                case KeyEvent.VK_A:
                    CatDogMouse.KEYINPUT = 'W';
                    //System.out.print("W");
                    break;
                case KeyEvent.VK_RIGHT:
                case KeyEvent.VK_D:
                    CatDogMouse.KEYINPUT = 'E';
                    //System.out.print("E");
                    break;
                //System.out.print("E");


            }
        }
    }
}

이 클래스를 다른 메인이 있는 클래스에서 불러오는데요

어쩔때는 키보드 입력이 들어오는데 어쩔때는 안들어오는데 왜 그런거죠?