javaapplet找不到符号

package twoappletscom;
//Web页内两个Apple通信，在同一网页中建立两个Applet的通信。
import java.awt.*;
import java.awt.event.*;
import java.applet.*;
public class SendApplet extends Applet{
TextField tfSend = new TextField("你好，能收到信息了吗？",20);//定义文本框
Button btnSend =new Button("发送到Receive");//定义发送按钮
public void init(){
setLayout(new FlowLayout());
add(tfSend);
add(btnSend);
}
public boolean ActionListener(Event ev,Object obj){//处理按钮事件
if (ev.target instanceof Button){ //发生按钮事件
String msgSend=tfSend.getText();//从文本框取出文本
ReceiveApplet receiveApplet=(receiveApplet)getAppletContext().getApplet("ReceiveApplet") ;//建立ReceiveApplet的实例
if(receiveApplet !=null){
receiveApplet.AppendText(msgSend);
return true; }