Java Applet JTextField不打印输入的文本

Question

我正在按照stanford.edu下学习java的编程方法课程，我尝试了一个程序，根据JTextField中使用的字体更改标签的字体，它响应输入键事件但它是不在JTextField中打印任何内容，而且我面临的一个问题是，当我展开窗口时，一切都是空白的，只显示窗口。我该怎样解决这个问题？

import acm.program.*;
import acm.graphics.*;
import acm.gui.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.JApplet;
public class EnterText extends GraphicsProgram {
    public void init(){
        //System.out.println("hello");
        fontfield=new JTextField(MAX_FONT_NAME);
         fontfield.setText("Enter your question here.");
        this.fontfield.addActionListener(this);
         fontfield.selectAll();
        add(fontfield,SOUTH);


        add(new JLabel("FONT"),SOUTH);

        lasty=0;

        lastlabel=new GLabel(str);

        addGLabel(lastlabel);
        addActionListeners();
        addMouseListeners();
    }
    public void actionPerformed(ActionEvent e){
        //System.out.println("hello");
        if(e.getSource()==fontfield){
        //  println("hello" + fontfield.getText());
            GLabel label=new GLabel("Hello");
            label.setFont(lastlabel.getFont());
            label.setFont(fontfield.getText());

            addGLabel(label);
            lastlabel=label;
        }
    }

    private void addGLabel(GLabel label){
        //System.out.println("hello");
        lasty +=label.getHeight();
        lasty +=lastlabel.getDescent()-label.getDescent();
        add(label,LEFT_MARGIN,lasty);
    }


private static final int MAX_FONT_NAME=150;
private static final int LEFT_MARGIN=30;
private static final  String str="Hello Java";
private JTextField fontfield;
private GLabel lastlabel;
private double lasty;

}