Design patterns interview
Q17. What is Session Façade pattern?
Ans. This pattern hides the complexity of business components and centralizes the workflow. It provides course-grained interfaces to the clients which reduces the remote method overhead. This pattern fits well with declarative transactions and security management.
Q18. What is Value Object Assembler pattern?
Ans. This pattern allows for composing a Value Object from different sources which could be EJBs, DAOs or Java objects.
Q19. What is Value List Handler pattern?
Ans. This pattern provides a sound solution for query execution and results processing.
Q20. What is Service Locator pattern?
Ans. It provides a solution for looking-up, creating and locating services and encapsulating their complexity. It provides a single point of control and it also improves performance.
Q21. What is Data Access Object pattern?
Ans. It provides a flexible and transparent access to the data, abstracts the data sources and hides the complexity of Data persistence layer. This pattern provides for loose coupling between business and data persistence layer.
Q22. What is EJB Command pattern?
Ans. Session Façade and EJB Command patterns are competitor patterns. It wraps business logic in command beans, decouples the client and business logic tier, and reduces the number of remote method invocations.
Q23. What is Version Number pattern?
Ans. This pattern is used for transaction and persistence and provides a solution for maintaining consistency and protects against concurrency. Every time a data is fetched from the database, it comes out with a version number which is saved in the database. Once any update is requested on the same row of the database, this version is checked. If the version is same, the update is allowed else not.
Q24. What all patterns are used to improve performance and scalability of the application?
Ans. VO, Session Façade, Business Delegate and Service Locator.
Q25. What design patterns could be used to manage security?
Ans. Single Access Point, Check point and Role patterns.