同一个包中的一个文件怎么不能引用另一个文件中的jLabel 啊，求助各位大哥帮帮忙，小弟的毕业设计好困难啊


这是定义jlabel的文件：
package booksale;import javax.swing.*;
import java.awt.*;
import java.util.*;
/**
 * <p>Title: 图书销售管理系统</p>
 * <p>Description: </p>
 * <p>Copyright: Copyright (c) 2006</p>
 * <p>Company: </p>
 * @author 王康
 * @version 1.0
 */public class Operate_Frame extends JFrame {
    JPanel jPanel1 = new JPanel();
  JLabel jLabel1 = new JLabel();
  JMenuBar jMenuBar1 = new JMenuBar();
  JMenu jMenu1 = new JMenu();
  JMenu jMenu2 = new JMenu();
  JMenu jMenu3 = new JMenu();
  JMenu jMenu4 = new JMenu();
  JMenu jMenu5 = new JMenu();
  BorderLayout borderLayout1 = new BorderLayout();
  FlowLayout flowLayout1 = new FlowLayout();
  JPanel jPanel2 = new JPanel();
  GridLayout gridLayout1 = new GridLayout(7,1);
  JButton rcls = new JButton();
  JButton jsq = new JButton();
  JButton tscx = new JButton();
  JButton xsth = new JButton();
  JButton rcpf = new JButton();
  JPanel jPanel3 = new JPanel();
  JLabel jLabel3 = new JLabel();
  BorderLayout borderLayout2 = new BorderLayout();
    JPanel jPanel4 = new JPanel();
  GridLayout gridLayout2 = new GridLayout(2,1);
  JLabel jLabel2 = new JLabel();
   JLabel jLabel4 = new JLabel();
   JLabel jLabel5 = new JLabel();  public Operate_Frame() {
    try {
      jbInit();
      DisTime();
    }
    catch(Exception e) {
      e.printStackTrace();
    }
  }
  private void jbInit() throws Exception {
    this.getContentPane().setBackground(new Color(217, 217, 223 ));
    this.setFont(new java.awt.Font("Serif", 1, 15));
    this.setJMenuBar(jMenuBar1);
    this.setTitle("图书销售管理系统");
    this.getContentPane().setLayout(borderLayout1);
       jPanel1.setLayout(flowLayout1);
    jLabel1.setHorizontalAlignment(SwingConstants.LEFT);
    jLabel1.setIcon(image2);
    jMenu1.setFont(new java.awt.Font("Serif", 1, 15));
    jMenu1.setToolTipText("");
    jMenu1.setText("日常业务    ");
   // jMenu1.setArmed(true);
        jMenuBar1.setOpaque(true);
    jMenuBar1.setRequestFocusEnabled(true);
    jMenuBar1.setToolTipText("");
    jMenuBar1.setMargin(new Insets(0, 0, 1, 1));
    jPanel1.setBackground(new Color(217, 217, 223));
    jPanel2.setLayout(gridLayout1);
    rcls.setBackground(new Color(217, 217, 223));
    rcls.setActionCommand("rcls");
    rcls.setHorizontalTextPosition(SwingConstants.CENTER);
    rcls.setIcon(image7);
    rcls.setText("日常零售");
    rcls.setVerticalAlignment(SwingConstants.CENTER);
    rcls.setVerticalTextPosition(SwingConstants.BOTTOM);
    jsq.setBackground(new Color(217, 217, 223));
    jsq.setActionCommand("jsq");
    jsq.setHorizontalTextPosition(SwingConstants.CENTER);
    jsq.setIcon(image9);
    jsq.setText("计算器");
    jsq.setVerticalTextPosition(SwingConstants.BOTTOM);
    tscx.setBackground(new Color(217, 217, 223));
    tscx.setActionCommand("tscx");
    tscx.setHorizontalTextPosition(SwingConstants.CENTER);
    tscx.setIcon(image11);
    tscx.setText("图书查询");
    tscx.setVerticalTextPosition(SwingConstants.BOTTOM);
    xsth.setBackground(new Color(217, 217, 223));
    xsth.setActionCommand("xsth");
    xsth.setHorizontalTextPosition(SwingConstants.CENTER);
    xsth.setIcon(image10);
    xsth.setText("销售退货");
    xsth.setVerticalTextPosition(SwingConstants.BOTTOM);
    rcpf.setBackground(new Color(217, 217, 223));
    rcpf.setVerifyInputWhenFocusTarget(true);
    rcpf.setActionCommand("rcpf");
    rcpf.setHorizontalAlignment(SwingConstants.CENTER);
    rcpf.setHorizontalTextPosition(SwingConstants.CENTER);
    rcpf.setIcon(image8);
    rcpf.setText("日常批发");
    rcpf.setVerticalAlignment(SwingConstants.CENTER);
    rcpf.setVerticalTextPosition(SwingConstants.BOTTOM);
    jPanel3.setBackground(new Color(217, 217, 223));
    jPanel3.setLayout(borderLayout2);
    jLabel3.setHorizontalAlignment(SwingConstants.CENTER);
    jLabel3.setHorizontalTextPosition(SwingConstants.CENTER);
    jLabel3.setIcon(image12);
    jPanel2.setBackground(new Color(217, 217, 223));
          jPanel4.setLayout(gridLayout2);
    jLabel2.setFont(new java.awt.Font("Serif", 0, 18));
    jLabel2.setText("                当前时间:              ");
    jPanel4.setBackground(new Color(217, 217, 223));
    gridLayout2.setRows(3);
    jLabel5.setText("jLabel5");
    this.getContentPane().add(jPanel1, BorderLayout.NORTH);
    jPanel1.add(jLabel1, null);
    jPanel1.add(jPanel4, null);
    jPanel4.add(jLabel2, null);
    jPanel4.add(jLabel5, null);
    jPanel4.add(jLabel4, null);
    this.getContentPane().add(jPanel2, BorderLayout.WEST);
    jPanel2.add(rcls, null);
    jPanel2.add(rcpf, null);
    jPanel2.add(xsth, null);
    jPanel2.add(tscx, null);
    jPanel2.add(jsq, null);
    this.getContentPane().add(jPanel3, BorderLayout.CENTER);
    jPanel3.add(jLabel3, BorderLayout.EAST);
         Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
    this.setSize(screenSize);
    this.show();
  }
*********************************************************************
这是引用jlabel4 和jLabel5的文件package booksale;
import java.util.*;
import java.awt.*;
import javax.swing.*;
import booksale.Operate_Frame;/**
 * <p>Title: 图书销售管理系统</p>
 * <p>Description: </p>
 * <p>Copyright: Copyright (c) 2006</p>
 * <p>Company: </p>
 * @author 王康
 * @version 1.0
 */ class DisTime extends Thread{
     
     Calendar cal = Calendar.getInstance();
     String nian = Integer.toString(cal.get(Calendar.YEAR));
     String yue = Integer.toString(cal.get(Calendar.MONTH));
     String ri = Integer.toString(cal.get(Calendar.MONDAY));
     String shi = Integer.toString(cal.get(Calendar.HOUR_OF_DAY));
     String fen = Integer.toString(cal.get(Calendar.MINUTE));
     String miao = Integer.toString(cal.get(Calendar.SECOND));
          public  void run(){
       while(true){
         jLabel4.setText("             " + nian + "年" + yue + "月" + ri + "日");
         jLabel5.setText("             " + shi + ":"+ fen + ":"+ miao);
         try{
           Thread.sleep(1000);
         }
         catch (InterruptedException e) {
                          }       }
     }}