Why does the command in Java not work when working with input?

Question

Java

The point is this. Here is the code:

try {
        
        connect = server.accept();
        output = new ObjectOutputStream(connect.getOutputStream());
        input = new ObjectInputStream(connect.getInputStream());
        output.writeObject("Сообщение получено! (" + input.readObject() + ")");
        System.out.println("Client write: " + (String)input.readObject());  //<----
        
      } catch (UnknownHostException e) {
        e.printStackTrace();
      } catch (IOException e) {
        e.printStackTrace();
      } catch (HeadlessException e) {
        e.printStackTrace();
      } catch (ClassNotFoundException e) {
        e.printStackTrace();
      }

Why is output.writeObject("Message received! (" + input.readObject() + ")"); but the subsequent command is not. (I showed it with an arrow)

Answer 1

It is necessary that the second Object be written to the input.
If you set two copies. applications with this code (i.e. read, then write, then expect to receive it), try output.flush() after output.writeObject
Also in this case (when the application is both a server and a client for itself), it matters:
1. initialization of ObjectOutputStream before ObjectInputStream
2. so that there is a writeObject before reading readObject, because During initialization, ObjectInputStream waits for people to write to it immediately, otherwise it blocks the stream.
In any case, there is blocking input / output, so you can’t do without a single thread.