UML class diagrams basics in LLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Identify the correct UML class diagram element

Which UML class diagram element represents a blueprint for objects, including attributes and methods?

A Class

B Object

C Package

D Interface

💡 Hint

Think about what defines the structure and behavior of objects in UML.

A Class is a blueprint that defines attributes and methods for objects. An Object is an instance of a class. A Package groups classes. An Interface defines a contract without implementation.

❓ Architecture

intermediate

Determine the correct relationship type in UML class diagrams

In a UML class diagram, which relationship type shows that one class owns or contains another class as a part?

A Dependency

B Aggregation

C Inheritance

D Association

💡 Hint

Consider the difference between whole-part relationships and simple links.

Aggregation represents a whole-part relationship where the part can exist independently. Association is a general link. Inheritance shows a parent-child class relationship. Dependency is a weaker usage link.

❓ scaling

advanced

Estimate the number of classes needed for a library management system UML diagram

You are designing a UML class diagram for a library system with books, members, loans, and staff. Which is the most reasonable number of classes to represent these entities and their relationships?

A 4 classes: Book, Member, Loan, Staff

B 20 classes including all possible details and external systems

C 2 classes: Book and Member

D 10 classes including Book, Member, Loan, Staff, Catalog, Reservation, Fine, Librarian, Publisher, Author

💡 Hint

Think about capturing main entities and their interactions without overcomplicating.

Option D balances detail and simplicity by including main entities and related concepts. Option D is too simple, missing key parts. Option D misses important entities. Option D is too complex for a basic UML diagram.

❓ tradeoff

advanced

Choose the best UML relationship for representing a strict inheritance hierarchy

Which UML relationship should you use to show that one class is a specialized version of another, inheriting its attributes and methods?

A Association

B Aggregation

C Inheritance (Generalization)

D Dependency

💡 Hint

Think about the 'is-a' relationship in object-oriented design.

Inheritance (Generalization) represents an 'is-a' relationship where a subclass inherits from a superclass. Other relationships do not express this hierarchy.

❓ component

expert

Trace the request flow in a UML class diagram for a user login process

Given a UML class diagram with classes: UserInterface, AuthController, UserService, and Database, which sequence correctly represents the flow of a login request?

A 1,2,3,4,5,6

B 1,3,2,4,5,6

C 2,1,3,4,5,6

D 1,2,4,3,5,6

💡 Hint

Follow the logical order of method calls from UI to database and back.

The correct flow starts with the UI sending data to the controller, which calls the service, which queries the database, then responses flow back in reverse order.