我用Java代码编写的一个客户端界面Client.java，我在编写个登录界面Login.java后，

我在Login里面创建了Client对象，想让登陆成功后，就打开客户端来着，结果打开时打开了，但是却发现原先客户端的界面发生了改变，这是为什么呢

mport java.awt.HeadlessException;import java.awt.event.ActionEvent;import java.awt.event.ActionListener;import javax.swing.ImageIcon;import javax.swing.JButton;import javax.swing.JFrame;import javax.swing.JLabel;import javax.swing.JOptionPane;import javax.swing.JPanel;import javax.swing.JPasswordField;import javax.swing.JTextField;@SuppressWarnings("serial")public class MainFrame extends JFrame {JLabel lbl1 = new JLabel("用户名:");JLabel lbl2 = new JLabel("密 码:");JTextField txt = new JTextField("admin",20);JPasswordField pwd = new JPasswordField(20);JButton btn = new JButton("登录");JPanel pnl = new JPanel();private int error = 0;public MainFrame(String title) throws HeadlessException {super(title);init();}private void init() {this.setResizable(false);pwd.setEchoChar('*');pnl.add(lbl1);pnl.add(txt);pnl.add(lbl2);pnl.add(pwd);pnl.add(btn);this.getContentPane().add(pnl);btn.addActionListener(new ActionListener() {@Overridepublic void actionPerformed(ActionEvent e) {if ("admin".equals(new String(pwd.getPassword()))){pnl.removeAll();JLabel lbl3 = new JLabel();ImageIcon icon = new ImageIcon(this.getClass().getResource("pic.jpg"));lbl3.setIcon(icon);pnl.add(lbl3);}else{if(error < 3){JOptionPane.showMessageDialog(null,"密码输入错误，请再试一次");error++;}else{JOptionPane.showMessageDialog(null,"对不起，您不是合法用户");txt.setEnabled(false);pwd.setEnabled(false);btn.setEnabled(false);}}}});}public static void main(String[] args) {MainFrame frm = new MainFrame("测试");frm.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);frm.setBounds(100, 100, 300, 120);frm.setVisible(true);}}