运行 Server 类（使用 java server 命令）时出现异常，如下所示（我已经启动 rmiregistry，使用 start rmiregistry 命令）。可能是什么问题呢？
C:\Users\william\Desktop\HelloWorld\Server>java Server
java.rmi.ServerException: RemoteException occurred in server thread; nested exce
ption is:
java.rmi.UnmarshalException: error unmarshalling arguments; nested excep
tion is:
java.lang.ClassNotFoundException: Hello
at sun.rmi.server.UnicastServerRef.oldDispatch(UnicastServerRef.java:419
)
at sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:267)
at sun.rmi.transport.Transport$1.run(Transport.java:177)
at sun.rmi.transport.Transport$1.run(Transport.java:174)
at java.security.AccessController.doPrivileged(Native Method)
at sun.rmi.transport.Transport.serviceCall(Transport.java:173)
at sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:5
53)
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(TCPTranspor
t.java:808)
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport
.java:667)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.
java:1110)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor
.java:603)
at java.lang.Thread.run(Thread.java:722)
at sun.rmi.transport.StreamRemoteCall.exceptionReceivedFromServer(Unknow
n Source)
at sun.rmi.transport.StreamRemoteCall.executeCall(Unknown Source)
at sun.rmi.server.UnicastRef.invoke(Unknown Source)
at sun.rmi.registry.RegistryImpl_Stub.bind(Unknown Source)
at Server.main(Server.java:61)
Caused by: java.rmi.UnmarshalException: error unmarshalling arguments; nested ex
ception is:
java.lang.ClassNotFoundException: Hello
at sun.rmi.registry.RegistryImpl_Skel.dispatch(Unknown Source)
at sun.rmi.server.UnicastServerRef.oldDispatch(UnicastServerRef.java:409
)
at sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:267)
at sun.rmi.transport.Transport$1.run(Transport.java:177)
at sun.rmi.transport.Transport$1.run(Transport.java:174)
at java.security.AccessController.doPrivileged(Native Method)
at sun.rmi.transport.Transport.serviceCall(Transport.java:173)
at sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:5
53)
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(TCPTranspor
t.java:808)
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport
.java:667)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.
java:1110)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor
.java:603)
at java.lang.Thread.run(Thread.java:722)
Caused by: java.lang.ClassNotFoundException: Hello
at java.net.URLClassLoader$1.run(URLClassLoader.java:366)
at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
at java.lang.ClassLoader.loadClass(ClassLoader.java:423)
at java.lang.ClassLoader.loadClass(ClassLoader.java:356)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:264)
at sun.rmi.server.LoaderHandler.loadProxyInterfaces(LoaderHandler.java:7
30)
at sun.rmi.server.LoaderHandler.loadProxyClass(LoaderHandler.java:674)
at sun.rmi.server.LoaderHandler.loadProxyClass(LoaderHandler.java:611)
at java.rmi.server.RMIClassLoader$2.loadProxyClass(RMIClassLoader.java:6
46)
at java.rmi.server.RMIClassLoader.loadProxyClass(RMIClassLoader.java:311
)
at sun.rmi.server.MarshalInputStream.resolveProxyClass(MarshalInputStrea
m.java:257)
at java.io.ObjectInputStream.readProxyDesc(ObjectInputStream.java:1549)
at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1511)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1
750)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1347)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:369)
... 13 more