CS2002 - Week 8 - Software Architecture & Design Patterns

Why use design patterns?

• Reusability: Pre-tested solutions

• Communication: Shared vocabulary

• Maintainability: Organised code

• Scalability: Adaptable structure

How does the Singleton pattern ensure a single instance?

Using a private constructor, static instance variable, and public getInstance() method

Name two creational patterns and their purposes

• Factory: Creates objects without specifying classes

• Builder: Constructs complex objects step-by-step

What are the 3 MVC components?

1. Model: Manages data

2. View: Displays data

3. Controller: Handles input

MVC flow for a bank transfer

User -> Controller (initiateTransfer)

Controller -> Model (validateTransfer, updateBalance)

Controller -> View (displayUpdateBalance)

MVC maintainability

Changes to one component (e.g View) don't affect others (Model/Controller)

Adapter pattern

Incompatible interfaces -> compatible

Decorator pattern

Adds responsibilities dynamically

Observer pattern

Objects (observers) get notified of change

Why is MVC easier to test?

Components are isolated

How to make Singleton thread-safe?

Use synchronised in getInstance() or static initialisation

Name an MVC variant

MVVM (Model-View-View-Model) for data-binding (e.g. Angular)

When should you use design patterns?

When they solve a specific problem - not as a default. Overuse adds complexity

Name two structural patterns

• Adapter: Incompatible interfaces -> compatible

• Decorator: Adds responsibilities dynamically

What does the Model do in MVC?

Stores data, Enforces business rules, Notifies View of updates

What is the View’s role in MVC?

Displays data from Model, No business logic, Updates when Model changes

What does the Controller handle?

Processes user input, Updates Model, Refreshes View