java rmi

刚学习了rmi，照着书上抄了一遍，可是报出异常，实在不知道怎么解决
Java code:

public interface HelloService extends Remote {
public String echo(String msg) throws RemoteException;

public Date getTime() throws RemoteException;
}


Java code:

public class HelloServiceImpl extends UnicastRemoteObject implements
HelloService {
private String name;

public HelloServiceImpl(String name) throws RemoteException {
this.name = name;
}

public String echo(String msg) throws RemoteException {
System.out.println(name + ":use the echo() method");
return "echo:" + msg + "from" + name;
}

public Date getTime() throws RemoteException {
System.out.println(name + ":use the getTime() method");
return new Date();
}
}


Java code:

public class SimpleServer1 {

public static void main(String[] args) {

try {
HelloService service1 = new HelloServiceImpl("service1");
HelloService service2 = new HelloServiceImpl("service2");