The project done for the first-year course computer communications.
Instructions for using ChatServer.java and ChatClient.java:
Sending a public message: When the app asks you for a name of a recipient write EVERYONE.
Sending a private message:
When the app asks you for a name of a recipient, write the name of a person,
you want to send a message to.
If the name is not valid, you will get a message:
User "username" does not exist. Try again with different username.
If you have already sent a message, you have to confirm that you want to send another one with typing YES.