Class Diagram of WhatsApp (Explanation)

Overview:

A class diagram in UML (Unified Modeling Language) helps model the static structure of a system by showing its classes, attributes, operations (methods), and the relationships among objects. For WhatsApp, this diagram focuses on users, messaging, media handling, group management, and calling features.

Key Classes and Their Responsibilities:

1. User

Attributes:

• userId: String
• name: String
• phoneNumber: String
• status: String
• lastSeen: DateTime

Methods:

• sendMessage(msg: Message): void
• makeCall(receiver: User, type: CallType): void
• updateStatus(status: String): void

2. Message

Attributes:

• messageId: String
• sender: User
• receiver: User
• content: String
• timestamp: DateTime
• messageType: Enum (TEXT, IMAGE, VIDEO, DOCUMENT)

Methods:

• encrypt(): void
• decrypt(): void

3. Chat

Attributes:

• chatId: String
• participants: List<User>
• messages: List<Message>

Methods:

• addMessage(msg: Message): void
• deleteMessage(msgId: String): void

4. GroupChat (inherits from Chat)

Attributes:

• groupName: String
• admin: User

Methods:

• addUser(user: User): void
• removeUser(user: User): void
• assignNewAdmin(newAdmin: User): void

5. Call

Attributes:

• callId: String
• caller: User
• receiver: User
• startTime: DateTime
• endTime: DateTime
• callType: Enum (VOICE, VIDEO)

Methods:

• startCall(): void
• endCall(): void

6. Media

Attributes:

• mediaId: String
• fileType: Enum (IMAGE, VIDEO, AUDIO, DOCUMENT)
• filePath: String
• uploadedBy: User

Methods:

• upload(): void
• download(): void

Relationships:

• User ↔ Chat: Many-to-many (a user can have multiple chats, and each chat can involve multiple users)
• Chat → Message: One-to-many (each chat has a list of messages)
• Message ↔ User: Each message has one sender and one receiver (or many in group)
• GroupChat ⊂ Chat: Inheritance (GroupChat is a specialized form of Chat)
• User ↔ Call: A user can initiate or receive many calls
• Message → Media: A message can be associated with a media file (optional)

Teaching Tips:

• Emphasize the separation of concerns: messaging logic in Message, media management in Media, and user behavior in User.
• Highlight the use of inheritance between Chat and GroupChat.
• Point out associations and multiplicity (e.g., one user ↔ many chats).
• Discuss how methods are tied to real-world features (like makeCall() or encrypt()).