I see that you are trying to connect the socket by using the following syntax:
input_socket = Socket(host, port);
This is causing the issue. For creating a Java object inside MATLAB you need to use the function 'javaObject'.
See the following documentation link for more information:
For example, for creating a socket you can use the following command:
client = javaObject('java.net.Socket', 'localhost', 4000);
For sending data from the client to server:
outToServer = client.getOutputStream();
out = javaObject('java.io.DataOutputStream', outToServer)
out.writeUTF('Hello from client');
For reading the data from the server:
inFromServer = client.getInputStream();
in = javaObject('java.io.DataInputStream', inFromServer)
I hope this helps!