💬 MessagingApp — Java Console Chat Application

A Java-based console messaging application built from scratch using core OOP principles. Supports both real-time 2-way communication over sockets and simple local messaging.

📌 Overview

This app simulates a messaging system where users can manage contacts, send/receive messages, and communicate in real time between two machines using a Server-Client architecture over sockets.

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Project Structure

The project contains 6 classes:

Files	Description
Contacts.java	Contact entity — stores name and phone number
Msg.java	Message entity — ID, sender, receiver, content, timestamp, delivery status, seen status. Implements Comparator<Msg> for timestamp-based sorting
MessagingApp.java	Core logic — parent class containing all 8 operations and shared state
Server.java	Server-side socket handler — extends MessagingApp, implements Runnable. Listens on port 6666
Client.java	Client-side socket handler — connects to server and handles send/receive
MessageDriver.java	Entry point — launches the app and displays the main menu

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⚙️ Features (8 Functions)

1. Add Contact

• Saves a contact's name and phone number into the contact list
• A while loop lets the user add as many contacts as needed

2. Delete Contact

• Deletes a contact by matching name and phone number
• Sets the contact to null and decrements the contact count

3. Display Contacts

• Displays all saved contacts using a nested loop (contacts stored in a 2D array)

4. Send Message

• Shows saved contacts before sending
• User types the recipient name — if it matches a saved contact, the message is sent
• Each message is automatically assigned:
  • A unique ID
  • A status (sent / not sent)
  • A seen flag (seen / unseen / can't be seen)
• Status logic based on msg_count conditions

5. Display Messages

• Messages are sorted by timestamp in descending order (latest first — just like real messaging apps)

if (messages[j].getTimestamp().compareTo(messages[j + 1].getTimestamp()) < 0) {
    // swap
}

• Sorting uses a comparison algorithm with the compareTo() method

6. Delete Message

• User provides a message ID
• That specific message is deleted from the list

7. Filter Messages

• View messages filtered by category using a switch-case menu:
  • Seen messages
  • Unseen messages
  • Sent messages
  • Unsent messages
  • Press e to exit

8. Search by Contact

• User searches for a specific contact
• Once matched, can view or delete that contact's messages filtered by: Seen / Unseen / Sent / Unsent

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🔌 2-Way Real-Time Communication (Socket-Based)

Option 4 in the menu enables live PC-to-PC chat using IP address + port.

How it works:

• One machine runs as the Server, the other as the Client
• The user can choose which role they want to take
• Both sides can send and receive messages simultaneously
• The chat ends when both sides type "exit"
• All messages (from both server and client) are stored

Key code used:

// Server side
try (ServerSocket ss = new ServerSocket(6666)) {
    Socket s = ss.accept();
    DataInputStream d = new DataInputStream(s.getInputStream());
    DataOutputStream dout = new DataOutputStream(s.getOutputStream());
    dout.writeUTF(msg);
    str = (String) d.readUTF();
     // bidirectional message handling
}

// Thread using Runnable interface
Thread s_thread = new Thread(new Runnable() {
    @Override
    public void run() {
        send_msg(sc, dout);
    }
});

Multithreading:

• The Runnable interface is implemented to handle sending and receiving at the same time
• One thread handles sending, another handles receiving — no blocking

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Simple Messages (Option 2 in Communication)

In addition to live socket chat, users can also send simple stored messages (non-real-time). These are also saved and can be displayed/filtered like other messages.

Screenshots

Main Menu

Display and Delete Contacts

Real - Communication using Sockets

As Server

As Client

Simple Messages

Displaly and Deleting Messages

Filter Messages

Seearch For Specific Contact

OOP Concepts Applied

Concept	Where Used
Classes & Objects	Contacts, Msg, Server, Client, MessagingApp
Encapsulation	Private fields in Msg and Contacts with getters/setters
Inheritance	Server extends MessagingApp to share state and methods
Interface Implementation	Server implements Runnable; Msg implements Comparator<Msg>
Composition	Msg holds a Contacts object as the receiver
Multithreading	Concurrent send/receive using Thread + Runnable
Sorting	Custom timestamp sort using compareTo() on LocalDateTime

🚀 How to Run

1. Compile all .java files
2. Run MessageDriver to start the app

# Compile
javac *.java

# Run
java MessageDriver

3. For 2-way communication:
   • Run the app on two machines on the same network
   • One selects Server, the other selects Client
   • Enter the Server's IP address on the Client side
   • Start chatting!
   • Type exit on either side to end the session

Port used: 6666

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👩‍💻 Author

Javairia Lateef
linkdin :https://www.linkedin.com/in/javairialateef

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