link－list java版

最近在学习数据结构的java表示方法（本来C描述的就学不好，但觉得到时做毕业论文可能有用，所以就再学）
这是一个link－list的例子，半图形界面，但还没有调试成功。
Main.java是运行主类，ListTest.java是图形界面，List.java是链表主代码

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

public class Main
{
  public static void main(String [] args)
  {
    ListTest listTest = new ListTest();
    listTest.init ();
    listTest.setSize (400,400);
    listTest.setVisible (true); 
  } 
}

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

public class ListTest extends JFrame
{
  PRivate JButton addAtF,addAtB,delFrF,delFrB,print;
  private JTextField input;
  private JLabel display;
  private JPanel p1,p2,p3,p4;
  private Container container;
  private List myList;
  Listener listener;
 
  public void init()
  {
   Listener listener = new Listener();
   List myList = new List();
   JTextField input = new JTextField(35);
   JLabel display = new JLabel("Result:   ");
   JButton addAtF = new JButton("addAtF");
   JButton addAtB = new JButton("addAtB");
   JButton delFrF = new JButton("delFrF");
   JButton delFrB = new JButton("delFrB");
   JButton print = new JButton("print");
   JPanel p1 = new JPanel();
   JPanel p2 = new JPanel();
   JPanel p3 = new JPanel();
   JPanel p4 = new JPanel();
  
 
   container = getContentPane();
   p1.add (input);
   p2.add (display);
   p3.add (addAtF);
   p3.add (addAtB);
   p3.add (delFrF);
   p3.add (delFrB);
   p3.add (print);
   p4.add (p1);
   p4.add (p2);
   p4.add (p3);
   container.add (p4);
  
   addAtF.addActionListener(listener);
   addAtB.addActionListener(listener);
   delFrF.addActionListener(listener);
   delFrB.addActionListener(listener);
   print.addActionListener(listener);
  
  
  }
 
  class Listener implements ActionListener
  {
   public void actionPerformed( ActionEvent e)
   {
      double ran = 100 * Math.random();
      int ranInt = (int)ran;
      Integer objInt = new Integer(ranInt);