Why is the socket not connecting on a real device?

Question

Java

running on emulator

Socket socket = new Socket("10.0.2.2", portNumber);

and everything works fine
. But on a real device, what I have not tried does not work, neither 127.0.0.1 nor 10.0.2.2
Error:

java.net.ConnectException: failed to connect to /127.0.0.1 (port 5000) from /:: (port 33717): connect failed: ECONNREFUSED (Connection refused)

Answer 1

Solved the problem by getting an IP using hostname -I (for linux)

Answer 2

127.0.0.1 is a request to itself (the phone calls itself)
10.0.2.2 is a request to the local network.
Show what the request for 10.0.2.2 says