Features Required:

User Authentication: Users should be able to create accounts, log in, and authenticate themselves to join video conferences.
Video Conferencing: Users should be able to initiate or join video conferences, enabling real-time video and audio communication with other participants.
Screen Sharing: Users should be able to share their screens during video conferences to display presentations, documents, or other content.
Audio Conferencing: Users should be able to communicate via audio-only calls when video is not required or available.
Chat and Messaging: Users should be able to send text messages, emojis, and other forms of communication during video conferences.
Meeting Scheduling: Users should be able to schedule and manage meetings, including setting start times, durations, and participant invitations.
Recording: The application should support recording video conferences for later playback or sharing.
Access Controls: Users should have the ability to control access to their video conferences, such as requiring passwords or waiting rooms for participants.

Design Patterns Involved or Used:

Observer Pattern: The Observer pattern can be used to notify participants about changes or updates during video conferences, such as new chat messages or screen sharing activities.
State Pattern: The State pattern can be used to manage the different states of a video conference, such as initializing, in progress, paused, or ended, and to handle state transitions.
Builder Pattern: The Builder pattern can be used to create and configure complex objects, such as meetings or conference sessions, with different options and parameters.
Proxy Pattern: The Proxy pattern can be used to manage access controls and permissions for joining video conferences, providing a level of indirection between clients and the actual video conferencing sessions.

Code: Classes Implementation Based on Patterns Mentioned Above

// User class
class User {
    private String username;
    private String password;
    // Other attributes and methods

    public User(String username, String password) {
        this.username = username;
        this.password = password;
    }

    // Getters and setters
}

// Meeting class
class Meeting {
    private String title;
    private Date startTime;
    private int duration;
    private List<User> participants;
    // Other attributes and methods

    public Meeting(String title, Date startTime, int duration) {
        this.title = title;
        this.startTime = startTime;
        this.duration = duration;
        this.participants = new ArrayList<>();
    }

    public void addParticipant(User participant) {
        participants.add(participant);
    }

    public void removeParticipant(User participant) {
        participants.remove(participant);
    }

    // Getters and setters
}

// VideoConference class
class VideoConference {
    private Meeting meeting;
    private List<User> participants;
    private VideoState state;
    // Other attributes and methods

    public VideoConference(Meeting meeting) {
        this.meeting = meeting;
        this.participants = new ArrayList<>();
        this.state = new InitializedState();
    }

    public void join(User participant) {
        state.join(this, participant);
    }

    public void leave(User participant) {
        state.leave(this, participant);
    }

    public void changeState(VideoState newState) {
        this.state = newState;
    }

    // Other operations related to video conferencing, such as start, pause, end, screen sharing, etc.
}

// VideoState interface
interface VideoState {
    void join(VideoConference videoConference, User participant);
    void leave(VideoConference videoConference, User participant);
}

// InitializedState class
class InitializedState implements VideoState {
    @Override
    public void join(VideoConference videoConference, User participant) {
        videoConference.addParticipant(participant);
        System.out.println(participant.getUsername() + " joined the video conference.");
    }

    @Override
    public void leave(VideoConference videoConference, User participant) {
        System.out.println(participant.getUsername() + " cannot leave before joining the conference.");
    }
}

// InProgressState class
class InProgressState implements VideoState {
    @Override
    public void join(VideoConference videoConference, User participant) {
        videoConference.addParticipant(participant);
        System.out.println(participant.getUsername() + " joined the video conference.");
    }

    @Override
    public void leave(VideoConference videoConference, User participant) {
        videoConference.removeParticipant(participant);
        System.out.println(participant.getUsername() + " left the video conference.");
    }
}

// Main Class
public class VideoConferencingApp {
    public static void main(String[] args) {
        // Create users
        User user1 = new User("user1", "password1");
        User user2 = new User("user2", "password2");

        // Create a meeting
        Meeting meeting = new Meeting("Team Meeting", new Date(), 60);
        meeting.addParticipant(user1);

        // Create a video conference
        VideoConference videoConference = new VideoConference(meeting);

        // Join the video conference
        videoConference.join(user1);
        videoConference.join(user2);

        // Leave the video conference
        videoConference.leave(user1);
        videoConference.leave(user2);
    }
}

In this code example, the User class represents a user of the video conferencing application, the Meeting class represents a scheduled meeting, and the VideoConference class represents a video conferencing session. The VideoState interface and its implementations (InitializedState and InProgressState) represent the different states of a video conference.

The code demonstrates the usage of classes based on the mentioned patterns, such as the Observer pattern for notifying participants about joining or leaving a conference, the State pattern for managing the different states of a video conference, the Builder pattern for creating meetings with different options, and the Proxy pattern for managing access controls.

Please note that this is a simplified example, and a complete implementation of a video conferencing application like Zoom involves more complex components, such as audio and video streaming, chat messaging, screen sharing, and networking protocols.

Design (LLD) a video conferencing application like Zoom - Machine Coding