Composition over inheritance in LLD - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is composition in system design?

Composition means building complex objects by combining simpler ones, like assembling Lego blocks to create a model. It focuses on 'has-a' relationships.

beginner

How does inheritance differ from composition?

Inheritance creates an 'is-a' relationship by extending a class, while composition builds objects by including other objects, promoting flexibility and reuse.

intermediate

Why is composition often preferred over inheritance?

Composition avoids tight coupling and rigid hierarchies, making systems easier to change and extend, like swapping parts in a machine instead of redesigning it.

beginner

Give an example of composition in a real-world system.

A car is composed of an engine, wheels, and seats. Each part can be changed independently without affecting the whole car's structure.

intermediate

What problem can inheritance cause that composition helps solve?

Inheritance can cause fragile base class problems and deep hierarchies that are hard to maintain. Composition allows changing behavior by replacing parts without breaking the system.

Which relationship best describes composition?

A 'is-a' relationship

B 'has-a' relationship

C Inheritance hierarchy

D Polymorphism only

Composition models 'has-a' relationships by combining objects.

What is a key benefit of using composition over inheritance?

A Forces tight coupling

B Creates deep class hierarchies

C Requires less code

D Easier to change parts independently

Composition allows swapping parts without affecting the whole system.

Which is a drawback of inheritance that composition avoids?

A Fragile base class problem

B Code reuse

C Encapsulation

D Modularity

Inheritance can cause fragile base classes that break when changed.

In system design, what does inheritance represent?

A 'is-a' relationship

B 'has-a' relationship

C Object composition

D Loose coupling

Inheritance models 'is-a' relationships by extending classes.

Which example best illustrates composition?

A A dog is an animal

B A manager extends employee

C A car has an engine and wheels

D A class inherits methods

A car composed of parts shows composition.

Explain composition over inheritance with a simple real-life example.

Think about how objects can be built from smaller parts.

Describe the main problems inheritance can cause and how composition helps avoid them.

Consider why changing a base class can break many subclasses.