Java实现ftp功能(源程序)

import sun.net.ftp.*;
import sun.net.*;
import java.awt.*;
import java.awt.event.*;
import java.applet.*;
import java.io.*;
public class FtpApplet extends Applet
{
FtpClient aftp;
DataOutputStream outputs ;
TelnetInputStream ins;
TelnetOutputStream outs;
TextArea lsArea;
Label    LblPrompt;
Button   BtnConn;
Button   BtnClose;
TextField  TxtUID;
TextField  TxtPWD;
TextField  TxtHost;
int ch;
public String a="没有连接主机";
        String hostname="";
public void init () {
setBackground(Color.white);
setLayout(new GridBagLayout());
GridBagConstraints GBC = new GridBagConstraints();
LblPrompt = new Label("没有连接主机";
LblPrompt.setAlignment(Label.LEFT);
BtnConn = new Button("连接";
BtnClose = new Button("断开";
BtnClose.enable(false);
TxtUID = new TextField("",15);
TxtPWD = new TextField("",15);
TxtPWD.setEchoCharacter(’*’);
TxtHost = new TextField("",20);
Label LblUID = new Label("User ID:";
Label LblPWD = new Label("PWD:";
Label LblHost = new Label("Host:";
lsArea = new TextArea(30,80);
lsArea.setEditable(false);
GBC.gridwidth= GridBagConstraints.REMAINDER;
GBC.fill     = GridBagConstraints.HORIZONTAL;
((GridBagLayout)getLayout()).setConstraints(LblPrompt,GBC);
add(LblPrompt);
GBC.gridwidth=1;
((GridBagLayout)getLayout()).setConstraints(LblHost,GBC);
add(LblHost);
GBC.gridwidth=GridBagConstraints.REMAINDER;
((GridBagLayout)getLayout()).setConstraints(TxtHost,GBC);
add(TxtHost);
GBC.gridwidth=1;
((GridBagLayout)getLayout()).setConstraints(LblUID,GBC);
add(LblUID);
GBC.gridwidth=1;
((GridBagLayout)getLayout()).setConstraints(TxtUID,GBC);
add(TxtUID);
GBC.gridwidth=1;
((GridBagLayout)getLayout()).setConstraints(LblPWD,GBC);
add(Lb