Course information

Course information • Old exam • Result and walkthrough • Resit • 30 november, 8.15-10.00 • Report • Should be under way‏

Helt irrelevant för kursen • First Lego League • 5 studenter sökes som domare • Programmering av legorobotar • 10-15-åringar • 7 november 09.00-15.00 • Molkoms högstadium (Nyed) • 100:-/h • www.hjernekraft.org

TDD, Pair Programming, Stand-ups SRP, OCP, LSP, DIP, ISP W7 – Processes and Principles

TDD – Uncle Bob’s 3 laws

TDD - FIRST

TDD – Red-Green-Refactor

Pair Programming • Always code in pairs • Switch driver/co-driver • Switch pairs • Knowledge spread

Stand-up meetings • Short and time-boxed • What have I done • What will I do • Problems

SRP (Single Responsibility Principle)‏ • A class should only have one reason to change • Cohesion • How focused a class is

Example - RBS • Who should know the price of a room/catering item/piece of equipment? • Domain vs storage

OCP (Open-Closed Principle)‏ • Software entities (classes, modules, functions, etc.) should be open for extension, but closed for modification • Existing clients should not have to care about future improvements • Future improvements should be possible • Abstration is the key • Refactoring

OCP (cont'd)‏ • "Open For Extension" - It is possible to extend the behavior of the module as the requirements of the application change (i.e. change the behavior of the module). • "Closed For Modification" - Extending the behavior of the module does not result in the changing of the source code or binary code of the module itself.

OCP - example

OCP - Bertrand Meyer • “A module will be said to be open if is still available for extension • For example, it should be possible to add fields to the data structures it contains, or new elements to the set of functions it performs” • “A module will be said to be closed if is available for use by other modules • This assumes that the module has been given a well-defined, stable description (the interface...)”

LSP (Liskov Substitution Principle)‏ • “What is wanted is something like the following substitution property: If for each object o1 of type S there is an object o2 of type T such that for all programs P defined in terms of T, the behavior of P is unchanged when o1 is substituted for o2, then S is a subtype of T. [Liskov88]“ • Subtypes must be substitutable for their base types [Uncle Bob]

LSP - example public class Rectangle { protected int _width; protected int _height; public int Width { get { return _width; } } public int Height { get { return _height; } } public virtual void SetWidth(int width)‏ { _width = width; } public virtual void SetHeight(int height)‏ { _height = height; } } public class Square: Rectangle { public override void SetWidth(int width)‏ { _width = width; _height = width; } public override void SetHeight(int height)‏ { _height = height; _width = _height; } }

LSP – example (cont'd)‏ [TestFixture] public class RectangleTests { [Test] public void AreaOfRectangle()‏ { Rectangle r = new Square(); r.Width = 5; r.Height = 2; // Will Fail - r is a square and sets // width and height equal to each other. Assert.IsEqual(r.Width * r.Height,10); } }

DIP (Dependency-Inversion Principle)‏ • Making your applications loosely coupled by not depending on concrete classes when appropriate, but abstractions • High-level modules should not depend on low-level modules. Both should depend on abstractions. • Abstractions should not depend on details. Details should depend on abstractions.

DIP - Good, bad, ugly

DIP – good for reuse • Low-level modules are already being reused • Buttons and other graphical objects • Lists and other containers • High-level modules are harder to reuse • DIP helps reusing higher modules • Decoupling from details

ISP (Interface Segregation Principle)‏ • Clients should not be forced to depend on methods that they do not use • Related to cohesion

ISP - Example • ATM • Deposit • Withdraw • Transfer • 3 different uses of the system • 3 different interfaces • You don't want to see stuff with no relevance

ISP – Example 2 Name Personal number Income IRS Name Pnr Grades Kau Artist

Course information