Behavioral Patterns - Visitor Pattern Exercise

behavioral-patterns-visitor-pattern-exercise

The Visitor Pattern represents an operation to be performed on elements of an object structure. Visitor lets you define a new operation without changing the classes of the elements on which it operates. In this exercise, we will create a bookstore inventory structure that collects books, movies, and music. We will add shared behaviors across this hierarchical structure by using the Visitor Pattern.

Reading Materials

  1. https://en.wikipedia.org/wiki/Visitor_pattern (15 minutes reading)

Practice Materials

  1. Use the Visitor Pattern to create a bookstore inventory that meets the following requirements:
  • the bookstore inventory collects books, movies, and music.
  • all these three media types have their own members and one common member - title
  • add one behavior to the media so that the operation can print out all the titles.
  • add second behavior to the media so that the operation can print out details of all media and the total count of media while the media is traversed.

Components:

  1. Visitor Interface (The operation that is shared across visited elements) - MediaVisitor
  2. Element Interface (The hierarchical structure that accepts the operation from a visitor) - Media
  3. Concrete Elements (The elements in the hierarchical structure that will be visited) - Book, Movie, Music
  4. Concrete Visitors (Each visitor will define one type of operation) - TitlePrintingVisitor, DetailPrintingVisitor
  5. Iterator for traversal (The root structure that holds the references to all the sub-elements) - Inventory

Tips

  • Visitors can have their own internal state to keep track of the elements they visit.

Solution

Bookstore Inventory Example

Questions to discuss

  1. What are the common use cases to apply the Template Method Pattern?
  2. What are the two major disadvantages of the Visitor Pattern?
  • Break Encapsulation
  • Difficult to add more subclasses to the hierarchical structure

Comments

Post a Comment

Popular posts from this blog

Distributed Transaction Management with REST and Try Confirm/Cancel Pattern

distributed-transaction-management-with-rest-and-try-confirm-cancel-patternThis article introduces how to manage transactions effectively in distributed REST services with Try Confirm/Cancel (TCC) pattern. It also provides a repository that is a simplified Java implementation for anyone who is interested in learning the TCC pattern. This repository attempts to trim the most of the common boilerplate, but only preserve the minimal that could be most straightforward to observe this pattern. It could be adapted to use any backend stack.Try Confirm/Cancel (TCC) PatternTCC is a distributed transactions pattern that fits in the stateless REST services. It is originally proposed by Guy Pardon, the creator of Atomikos.Useful ReferencesConference Speech By Guy PardonTCC for REST API (API specification)Spring Cloud TCC Example By ChrisAbout This RepositoryThis repository is a simplified Java implementation for anyone who is interested in learning the TCC pattern. This repo attempts to trim the …
Read more

Spring JMS and JPA XA Transactions with WebLogic

spring-jms-and-jpa-xa-transactions-with-weblogicThis article shows the configuration of using XA transactions with the resources managed by WebLogic server.There are three parts of configurations for this XA transactions to work - JMS, JPA and JTA. Both JMS and JPA are acquired through the JNDI registry and the XA transaction manager implementation uses the one from the WebLogic server. This configuration relies on WebLogic server. The concept should be similar and applicable to other JEE application servers. With these configurations, we could easily use @Transactional annotation on the services for XA transactions.JmsConfiguration.java Excerpt@ConfigurationpublicclassJmsConfiguration{// properties...@Beanpublic ConnectionFactory connectionFactory(){returnlookupByJndiTemplate(jmsConnectionFactory, ConnectionFactory.class);}@Beanpublic JndiTemplate jndiTemplate(){ JndiTemplate jndiTemplate =newJndiTemplate(); jndiTemplate.setEnvironment(getJndiProperties());return jndi…
Read more

Creating a Library Project for Spring Boot

creating-a-library-project-for-spring-bootThis article introduces the key points when creating a library for spring boot project.It could be common that over the years you have created a number of services that could be reused by other spring projects. It then makes sense to make the reusable modules such as a library and install it in your local repository for later use.Here are the key points to consider when building a spring boot library.release versionbuild plugindependency injectionautoconfigurationsRelease VersionTo guarantee spring boot works the way you expect, it is recommended to keep update the release versions of the library so that it supports some versions of the spring boot minor version. A good practice is to monitor change spring boot changelog and see if there are any conflicting dependencies that are used in the library project. If there is, introduce a new version to resolve the conflict.Build PluginIf the projects reference this library doesn’t compile through ma…
Read more