我试图从我的安卓手机发送一个对象到我的电脑，但我一直收到这个错误，它无法识别这个对象的类。这很奇怪，因为当我尝试将对象从计算机发送到自身时，它使用相同的方式工作。这两个包都有 User 类，并且它实现了 Serializable。请告诉我为什么会这样。
计算机（服务器）：
private ServerSocket server;
private ObjectInputStream input;
private Socket connection;
private User message;
public void brains() throws IOException {
while (true) {
System.out.println("waiting for connection...");
try {
server = new ServerSocket(4567, 100);
connection = server.accept();
System.out.println("you are now conected");
} catch (IOException ioException) {
ioException.printStackTrace();
}
System.out.println("Setting up Streams..");
input = new ObjectInputStream(connection.getInputStream());
try {
message = (User) input.readObject();
} catch (ClassNotFoundException ex) {
System.out.println("I dont know wtf");
}
System.out.print("the user ");
message.printUserName();
System.out.print(", used your app at ");
message.printTime();
System.out.println("");
System.out.println("Shutting down!");
try {
input.close();
connection.close();
server.close();
} catch (IOException ioException) {
ioException.printStackTrace();
}
}
}
电话（客户）：
private User user;
private Socket connection;
private ObjectOutputStream output;
public void run() {
try{
connection = new Socket (InetAddress.getByName(ip), 4567);
output = new ObjectOutputStream(connection.getOutputStream()) ;
user = new User("bla bla", "14:09");
output.writeObject(user);
output.flush();
}catch(Exception e){
System.out.print(e);
}finally{
try{
output.close();
connection.close();
}
catch(Exception e){
System.out.print(e);
}
}
}
这是控制台日志：
waiting for connection...
you are now conected
Setting up Streams..
Dont recognize the class
the user Exception in thread "main" java.lang.NullPointerException
at whosUsing.whosUsing.brains(whosUsing.java:34)
at whosUsing.test.main(test.java:9)