乒乓球问题，指方法的来回调用.
public class Boy extends Actor{
@Override public void send(String message,Actor to){
pln(this.name+" To "+to.name+":\""+message+"\"");
to.receive(message,this);
}
@Override public void receive(String message,Actor from){
char c = (char)(Math.random()*4+'a');
if(c!='b'){
String msg = message+" "+c;
send(msg,from);
}
}
}
对象a. send(String message,Actor to)代码中b..receive(message,this)，而b.receive()代码中自己又send()。原文地址：http://blog.csdn.net/yqj2065/article/details/39591119
