COMP2511

Tutorial 10

Today

If you did assignment-iii, please make sure you submit it following the instructions in the spec

No autogenerated UMLs
No ChatGPT blogs
Make the video accessible to the public
- We will not be chasing this up since marking will happen during week 11/12

By Alvin

Suppose:

I created a ResumeTemplate and gave it to everyone in the class
You can edit the content within each section of the template to match your personal information
But you cannot edit the structure of the template itself

Think of templates from MS word

UML Diagram

generateResume is the template method that can be split into smaller "steps"
Steps can be overridden by subclasses and they are the hook methods
Methods that have default implementation and cannot be overridden are final methods
- Why is generateResume final?

Behavioural design pattern that lets you

Define the skeleton (i.e. steps) of an algorithm in a super class
Override specific steps of the algorithm in subclasses without modifying the overall structure of the algorithm

Why use it?

Subclasses do not need to duplicate the entire algorithm each time
By only allowing subclasses to modify hook methods, they cannot accidentally break the algorithm

What is it?

Code Demo

Model how characters in a game can move around and attack other characters

A King can
- Move one square in any direction (including diagonally)
- Always deal 8 points of damage when attacking
A Queen can
- Move to any square in the same column, row or diagonal as her current position
- Deal 12 points of damage with a 1 in 3 chance or 6 points of damage otherwise
A Dragon can
- Move up, down, left or right
- Inflict 20 points of damage with a 1 in 6 change

Suppose:

I have different types of characters in a Game
If I want to allow users to save the game, I need to be able store information about the game onto disk
Convert information from the game into JSON files
But how can I convert instances of some class into a JSON file?

Add an interface JSONExport and implement it for every class that can be exported

What if now I can't edit the source code of these classes directly?

The game could be a legacy system, so the original authors don't want anyone to change the code anymore
The game could be developed by a different team in the company and they also they want other people messing with their code

Visitable: classes that need the new feature
- Must have an accept method that takes a visitor
Visitor: classes that will add a new feature to the visitable
- Must have a visit method for each type of visitable

UML Diagram

Code Demo

What is it?

Benefits

Behavioural design pattern that allow functionalities to be added to classes without needing to "open" them

When to use?

Obey the Open-close principle
Obey the Single responsibility principle because every new functionality is a new "visitor"

New operations need to be added to all elements of an existing object structure

Thank you all for a great term and good luck for your exams 🎉