Visitor Pattern

Visitor Pattern

Problem: How do I add extra functionalities to subclasses without violating open/closed principle.

Visitor Pattern

Problem: How do I add extra functionalities to subclasses without violating open/closed principle.

Visitor Pattern

Behavioural Pattern

• Adds extra functionality to class without modifying the original (abides by open closed principle)
• One class/interface (visitor) defines a computation/operation and another (visitable) is responsible for providing data access

Exam Tips

Exam Tips

• Practice good exam techniques.
• Get familiar with writing Java & Generics
• Learn the patterns and the differences (YouTube has some really good resources if you don't understand certain ones).
• Know code smells and methods of refactoring

Code Demo

Computer.java

Code Demo

In this scenario we have Computers, Keyboards and Mouses which all are of type ComputerComponent. We want to be able to 'visit' different types of Computer components by logging the following messages:

In particular though, anyone which is visiting a Computer must be validated prior to being able to visit.

Extend/modify the starter code to use the Visitor Pattern to allow different computer components to be visited.