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SOFT2201 Week 3 Tutorial UML and Implementation
UML
The Unified Modelling Language is a visual language that allows software designers to visualise data and functionality of their system and how they interact with each other. There are 5 different UML diagram types. In this tutorial we will be focusing on the class diagram.
Question 1: Heirarchy and Properties
You have been provided an example UML class model. This is a simple class heirarchy, outlining shared properties and functionality between the base class and sub-types.
Figure 1: Dog Class, illustrates the java code as a UML diagram As a class, discuss and answer the following:
• What is the parent class of Wolf?
• What properties are shared between DomesticDog and Wolf? • What methods are shared between DomesticDog and Wolf? • Outline the access level associated with each field
• Does either sub-type of Canine override one of its methods?
1
SOFT2201 UML and Implementation
Question 2: Associations
Analyse the UML diagram and identify and answer the following:
• Outline all the associations within the UML Diagram
• How many Aeroplanes can a Hanger contain? Annotate the multiplicity of the association
• How many Tickets can a Customer hold? Annotate the multiplicity of the association
• Identify any association relationships where an object cannot exist without at least one other type (Composition)
• Identify any aggregate relationship within the diagram
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GRASP Guidelines
GRASP is a mental toolset, a guideline to follow when designing software. Identifying pattern viola- tions can provide an understanding of flaws within the software architecture.
As a quick recap of the GRASP patterns.
• Information Expert, Assign a responsibility to the information expert – the class that has the information necessary to fulfill the responsibility.
• Creator, Responsibility of object creation.
• Controller, can represent two components of a system. 1. Represents the overall system, a root object which represents a major subsystem. 2. Represents a use case scenario within which the system operation occurs (a use-case or session controller).
• Low Coupling, how connected an object type is connecto to another type. Consider the assign- ment of responsibilities and any unncessary binding to other types.
• High Cohesion, Where responsibility of the element share common characteristics (properties, methods, associations, ..).
• Polymorphism, When related alternatives or behaviour vary by type, assign responsibility for the behaviour using polymorphic operations to the type for which the behaviour varies.
• Pure Fabrication, Assign a highly cohesive set of responsibilities to an artifical or convenience bahviour class (or type) that does not represent a problem concept-something made up, in order to support high cohesion, low coupling, and reuse.
• Indirection, Assign the responsibility to an intermediate object to mediate between other com- ponents or services, so that they are not directly coupled
• ProtectedVariations,Identifypointsofpredictedvariationorinstanbility;assignresponsibilties to create a stable interface around them.
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SOFT2201 UML and Implementation
Question 3: SOLID vs GRASP
Discuss with your class and tutor about SOLID and GRASP. Identify overlapping concepts between
the principles and discuss how each principle applies to software design.
Question 4: Critiquing a model
Given the following class diagram, discuss with your class about issues with the current application model.
Common issues that arise from improper modelling:
• Weak base classes
• Improper parent or interface type associated
• Repetitive logic and data
• Class dependent on other classes
• Classes performing more functionality than it should be • Misassigned responsibility to an object
Consider what GRASP or SOLID principles have been violated by the heirarchy.
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Question 5: Extract Pokemon
You have been given a file that stores pokemon data called pokedex.json. Use the simple-json library as a way to read the pokedex.json file and output the contents to the stdout.
You can add the dependency to your project by adding the following to the dependecies section in your gradle.build file.
implementation ’com.googlecode.json-simple:json-simple:1.1.1’
The element within pokedex.json file is in the following layout:
{
“kanto_no” : “type_1” : “type_2” : “pokemon” : name
,
,
,
index
SOFT2201 UML and Implementation
first_type
second_type
}
Importthefollowingtypesintoyourprojectandattempttoparsethepokedex.json file.
import org.json.simple.JSONArray;
import org.json.simple.JSONObject;
import org.json.simple.parser.JSONParser;
JSON-Simple provides some examples in its wiki, you can access this here.
Read the contents of the file into a String object and utilise the .parse method to interpret the
data into a JSONArray. You may need to apply a cast on the return result.
Question 6: Modelling
As a group, you will need to construct a UML class diagram, assigning responsibilty to elements identified. After you have finished mapping the UML class diagram, discuss and rationalise your decisions with your tutor.
You are designing an point of sale system for a bike shop, the bike shop sells variety of bicycles such as mountain, commuter, road, single speed and electronic bikes. A customer is able to purchase a bike, services (such as repairs and maintenance) or other products such as a tubes, locks, grips, helmets and lights.
To ensure the system can be audited and for orders to be managed, purchases are grouped by an order, one or more items that are purchases are incorporated in an order. Each order belongs to a customer. Each order has a total amount to be paid, payment method (BankTransfer, Cash, Credit) order number and payment date.
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Question 7: From design to code
Once you have modelled the application, implement your model and try and make a workable point of sale system using the existing interfaces within the app.
You will need to use the registerProduct method within the App class to make a Product selectable from UI.
Once you have implemented the interfaces correctly for the types within your model, ensure that the following features work:
• Items are accessible from the drop down menu
• When purchasing a type from the drop down, it will add an entry within the table • It will allow the user to specify quantity of a product
• It will output a csv containing the items purchased
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