Prompt:

A software application offers an online service (say, transforming images from one format into another) which can take a few seconds or minutes to complete. Currently, no message is prompted while the user is waiting for the service response. It is more desirable to extend this service by displaying a progress bar to inform the user of the progress. However, directly modifying the existing code is a bad idea because it may affect other clients of the existing online service.

Question 1 For the application above, pick the best-fit design pattern below that allows you to extend the system to meet the new needs.

Singleton

Object Pool

Filter

Read-Only Interface

Motivation

Composite

Builder

Prototype

Abstract Factory

Factory Method

Proxy

Immutable Objects

Object Comparision

Marker Interface

Java Cloneable Interface

Question 2. Based on the design pattern you chose above, draw UML class diagram that shows all the relationships, multiplicities, and important operations.