Visitor pattern in LLD - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the main purpose of the Visitor pattern?

The Visitor pattern lets you add new operations to objects without changing their classes. It separates an algorithm from the objects it works on.

beginner

In the Visitor pattern, what roles do 'Element' and 'Visitor' play?

Elements are objects that accept visitors. Visitors define operations to perform on elements. Elements have an 'accept' method that takes a visitor.

intermediate

Why is the Visitor pattern useful when you want to add new operations frequently?

Because you can add new visitor classes with new operations without changing the element classes, avoiding code changes and recompilation of elements.

intermediate

What is a common drawback of the Visitor pattern?

It can be hard to add new element types because you must update all visitor classes to handle the new element.

advanced

How does the Visitor pattern relate to the Open/Closed Principle?

It helps keep element classes closed for modification but open for extension by adding new visitors for new operations.

What method must an element implement to work with a visitor?

A accept(visitor)

B visit(element)

C execute(visitor)

D handle(visitor)

Elements implement an accept(visitor) method to allow visitors to perform operations on them.

Which of these is a benefit of using the Visitor pattern?

A Simplify element class hierarchy

B Easily add new element types without changing visitors

C Add new operations without changing element classes

D Avoid double dispatch

Visitor pattern allows adding new operations by creating new visitors, without modifying element classes.

What is a typical downside of the Visitor pattern?

A Hard to add new operations

B Visitors cannot access element data

C Elements must know visitor internals

D Hard to add new element types

Adding new element types requires updating all visitor classes, which can be cumbersome.

Which principle does the Visitor pattern help to follow?

A Single Responsibility Principle

B Open/Closed Principle

C Liskov Substitution Principle

D Dependency Inversion Principle

Visitor pattern keeps element classes closed for modification but open for extension via new visitors.

In the Visitor pattern, what is double dispatch?

A Selecting a method based on both visitor and element types

B Calling two methods in sequence

C Calling visitor twice on the same element

D Using two visitors on one element

Double dispatch means the operation depends on both the visitor and element types, enabling correct method selection.

Explain how the Visitor pattern separates operations from object structures and why this is useful.

Think about how you can add new features without touching existing code.

Describe a scenario where using the Visitor pattern would be beneficial and one where it might cause problems.

Consider how often operations or element types change.