Methods call using RMI in JAVA

Question

I’m starting to work with remote procedures in JAVA and I’m having trouble calling methods in sequence. In the code below, when I invoke the sayHello() method through the stub, the code works perfectly. However, when I call the sub() method, an error sequence is displayed. Someone could instruct me how to call other methods?

Client.java:

public class Client {

    private Client() {
    }
    public static void main(String[] args) {
        String host = (args.length < 1) ? null : args[0];

        try {
            Registry registry = LocateRegistry.getRegistry(host);
            Hello stub = (Hello) registry.lookup("Hello");

            /*
             * String response = stub.sayHello();     
             * System.out.println("response: " + response);
             */

            float result = stub.sub(10, 8);
            System.out.println(result);

        } catch (Exception e) {
            System.err.println("Client exception: " + e.toString());
         e.printStackTrace();
     }
}

Java server.:

    public class Server implements Hello {

    public Server() {
    }

    public String sayHello() {
        return "Hello, world!";
    }

    public float sum(float a, float b) {
        return a + b;
    }

    public float div(float a, float b) {
        if (b != 0) {
            a = a / b;
        } else {
            System.out.println("DIVISAO POR ZERO!");
            a = 0;
        }
        return a;
    }

    public float mult(float a, float b) {
        return a * b;
    }

    public float sub(float a, float b) {
        return a - b;
    }

    public static void main(String args[]) {

        try {
            Server obj = new Server();
            Hello stub = (Hello) UnicastRemoteObject.exportObject(obj, 0);

            // Bind the remote object's stub in the registry
            Registry registry = LocateRegistry.getRegistry();
            registry.bind("Hello", stub);

            System.err.println("Server ready");
        } catch (Exception e) {
            System.err.println("Server exception: " + e.toString());
            e.printStackTrace();
        }
    }
}

Hello.java:

public interface Hello extends Remote {
    float sum(float a, float b) throws RemoteException;

    float div(float a, float b) throws RemoteException;

    float mult(float a, float b) throws RemoteException;

    float sub(float a, float b) throws RemoteException;

    String sayHello() throws RemoteException;
}

Terrifying error message:

Client exception: java.rmi.ServerException: RemoteException occurred in server thread; nested exception is: 
    java.rmi.UnmarshalException: unrecognized method hash: method not supported by remote object
java.rmi.ServerException: RemoteException occurred in server thread; nested exception is: 
    java.rmi.UnmarshalException: unrecognized method hash: method not supported by remote object
    at java.rmi/sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:391)
    at java.rmi/sun.rmi.transport.Transport$1.run(Transport.java:200)
    at java.rmi/sun.rmi.transport.Transport$1.run(Transport.java:197)
    at java.base/java.security.AccessController.doPrivileged(Native Method)
    at java.rmi/sun.rmi.transport.Transport.serviceCall(Transport.java:196)
    at java.rmi/sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:562)
    at java.rmi/sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(TCPTransport.java:796)
    at java.rmi/sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.lambda$run$0(TCPTransport.java:677)
    at java.base/java.security.AccessController.doPrivileged(Native Method)
    at java.rmi/sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport.java:676)
    at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1135)
    at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
    at java.base/java.lang.Thread.run(Thread.java:844)
    at java.rmi/sun.rmi.transport.StreamRemoteCall.exceptionReceivedFromServer(StreamRemoteCall.java:283)
    at java.rmi/sun.rmi.transport.StreamRemoteCall.executeCall(StreamRemoteCall.java:260)
    at java.rmi/sun.rmi.server.UnicastRef.invoke(UnicastRef.java:161)
    at java.rmi/java.rmi.server.RemoteObjectInvocationHandler.invokeRemoteMethod(RemoteObjectInvocationHandler.java:209)
    at java.rmi/java.rmi.server.RemoteObjectInvocationHandler.invoke(RemoteObjectInvocationHandler.java:161)
    at com.sun.proxy.$Proxy0.sub(Unknown Source)
    at Client.main(Client.java:28)
Caused by: java.rmi.UnmarshalException: unrecognized method hash: method not supported by remote object
    at java.rmi/sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:324)
    at java.rmi/sun.rmi.transport.Transport$1.run(Transport.java:200)
    at java.rmi/sun.rmi.transport.Transport$1.run(Transport.java:197)
    at java.base/java.security.AccessController.doPrivileged(Native Method)
    at java.rmi/sun.rmi.transport.Transport.serviceCall(Transport.java:196)
    at java.rmi/sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:562)
    at java.rmi/sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(TCPTransport.java:796)
    at java.rmi/sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.lambda$run$0(TCPTransport.java:677)
    at java.base/java.security.AccessController.doPrivileged(Native Method)
    at java.rmi/sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport.java:676)
    at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1135)
    at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
    at java.base/java.lang.Thread.run(Thread.java:844)