Swing事件的一些小问题? 400 报错

package Ztest2;

import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;

import javax.swing.JButton;
import javax.swing.JFrame;

public class Demo2 extends JFrame implements KeyListener, ActionListener {

    private String direction;
    private JButton jb = new JButton("按钮1");

    public Demo2(String direction) {
        this.direction = direction;
        this.setLayout(new BorderLayout());
        this.setSize(400, 200);
        jb.addActionListener(this);
        this.add(jb, BorderLayout.NORTH);
        this.setVisible(true);
        this.addKeyListener(this);
        this.setDefaultCloseOperation(EXIT_ON_CLOSE);
        this.requestFocusInWindow();
    }

    @Override
    public void keyTyped(KeyEvent e) {
    }

    @Override
    public void keyPressed(KeyEvent e) {
        int k = e.getKeyCode();
        System.out.println(k);
        if (k == KeyEvent.VK_RIGHT) {
            System.out.println(direction);
        } else if (k == KeyEvent.VK_LEFT) {
            System.out.println(direction);
        } else if (k == KeyEvent.VK_DOWN) {
            System.out.println(direction);
        } else if (k == KeyEvent.VK_UP) {
            System.out.println(direction);
        }
    }

    @Override
    public void keyReleased(KeyEvent e) {
    }

    public static void main(String[] args) {
        Demo2 d2 = new Demo2("wocao");
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        Object o1 = e.getSource();
        System.out.println(o1);
        if (o1 == jb) {
            Thread t = new Thread() {

                public void run() {
                    while (true) {
                        System.out.println("haha");
                        try {
                            Thread.sleep(1000);
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                }
            };
            t.start();
        }
        this.requestFocusInWindow();
    }
}