When to use which behavioral pattern in LLD - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the main purpose of the Observer pattern?

The Observer pattern is used to notify multiple objects about changes in another object, promoting loose coupling between the subject and its observers.

beginner

When should you use the Strategy pattern?

Use the Strategy pattern when you want to define a family of algorithms, encapsulate each one, and make them interchangeable without changing the clients that use them.

intermediate

What problem does the Command pattern solve?

The Command pattern encapsulates a request as an object, allowing parameterization of clients with queues, requests, and operations, and supports undoable operations.

intermediate

In which scenario is the State pattern most useful?

The State pattern is useful when an object must change its behavior based on its internal state, making the state transitions explicit and easier to manage.

beginner

How does the Iterator pattern help in system design?

The Iterator pattern provides a way to access elements of a collection sequentially without exposing its underlying representation.

Which behavioral pattern is best for implementing undo functionality?

A Observer

B Command

C Strategy

D State

The Command pattern encapsulates requests and supports undo operations by storing commands.

If you want to change an object's behavior when its internal state changes, which pattern should you use?

A Strategy

B Observer

C Iterator

D State

The State pattern allows an object to alter its behavior when its internal state changes.

Which pattern allows multiple objects to be notified automatically when one object changes?

A Observer

B State

C Command

D Strategy

The Observer pattern defines a one-to-many dependency to notify observers of changes.

When should you use the Strategy pattern?

A To encapsulate interchangeable algorithms

B To traverse a collection

C To manage object state transitions

D To notify multiple objects about changes

Strategy pattern encapsulates interchangeable algorithms for flexible use.

Which pattern helps to access elements of a collection without exposing its structure?

A State

B Command

C Iterator

D Observer

Iterator pattern provides sequential access to collection elements without exposing internal structure.

Explain when and why you would use the Observer pattern in a system design.

Think about situations where many parts of a system need to react to changes in one part.

Describe the differences between the Strategy and State patterns and when to choose each.

Focus on who controls the behavior changes and what changes.