Class diagrams in LLD - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a class diagram in system design?

A class diagram is a visual representation that shows classes, their attributes, methods, and relationships in a system. It helps understand the structure of the system.

beginner

Name three types of relationships shown in class diagrams.

The three main relationships are: Association (a link between classes), Inheritance (one class inherits from another), and Aggregation/Composition (whole-part relationships).

intermediate

What is the difference between aggregation and composition in class diagrams?

Aggregation means a class has a part that can exist independently. Composition means the part cannot exist without the whole; it is a stronger relationship.

beginner

Why are class diagrams useful in software design?

They help visualize system structure, clarify how classes interact, guide coding, and improve communication among team members.

beginner

What does a class box typically contain in a class diagram?

A class box usually has three sections: the class name at the top, attributes (properties) in the middle, and methods (functions) at the bottom.

Which section of a class box lists the functions it can perform?

A Attributes section

B Methods section

C Class name section

D Relationships section

The methods section lists the functions or operations a class can perform.

What type of relationship shows one class inheriting from another?

A Association

B Aggregation

C Inheritance

D Composition

Inheritance means one class derives properties and behavior from another class.

In a class diagram, what does aggregation represent?

A A part that cannot exist without the whole

B A simple link between classes

C A class inheriting from another

D A part that can exist independently

Aggregation means the part can exist independently of the whole.

Which of these is NOT typically shown in a class diagram?

A User interface layout

B Class attributes

C Class methods

D Class relationships

User interface layout is not shown in class diagrams; they focus on class structure.

Why use class diagrams in software design?

A To visualize system structure and relationships

B To design database queries

C To write code faster

D To create user manuals

Class diagrams help visualize the system's structure and how classes relate.

Explain the main components of a class diagram and their purpose.

Think about the three sections of a class box and how classes connect.

Describe the differences between association, aggregation, and composition in class diagrams.

Consider how parts relate to wholes and if they can exist separately.