eclipse调试 true typeFont.open()行:不可用,该怎么解决

import java.awt.Color;import java.awt.EventQueue;import java.awt.event.ActionEvent;import java.awt.event.ActionListener;import javax.swing.JButton;import javax.swing.JFrame;import javax.swing.JPanel;public class BuggyButtonTest {    public static void main(String[] args) {        EventQueue.invokeLater(new Runnable() {            public void run() {                BuggyButtonTestFrame frame = new BuggyButtonTestFrame();                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);                frame.setVisible(true);            }        });    }}class BuggyButtonTestFrame extends JFrame {    public BuggyButtonTestFrame() {        setSize(DEFAULT_WIDTH, DEFAULT_HEIGHT);        setTitle("BuggyButtonTest");        setLocation(200, 300);                // add panel        BuggyButtonPanel panel = new BuggyButtonPanel();        add(panel);    }        private int DEFAULT_WIDTH = 200;    private int DEFAULT_HEIGHT = 300;    }class BuggyButtonPanel extends JPanel {    public BuggyButtonPanel() {        ActionListener listener = new ButtonListener();                JButton yellowButton = new JButton("yellow");        add(yellowButton);        yellowButton.addActionListener(listener);                JButton redButton = new JButton("red");        add(redButton);        redButton.addActionListener(listener);                JButton blueButton = new JButton("blue");        add(blueButton);        blueButton.addActionListener(listener);    }        private class ButtonListener implements ActionListener {        public void actionPerformed(ActionEvent event) {            String arg = event.getActionCommand();            if (arg.equals("yellow")) {                setBackground(Color.yellow);            } else if (arg.equals("red")) {                setBackground(Color.red);            } else if (arg.equals("blue")) {                setBackground(Color.blue);            }        }    }}