Software Engineering and Architecture (Many) Mandatory Reflections - PowerPoint PPT Presentation

Software Engineering and Architecture (Many) Mandatory Reflections And SE Hints ☺

Correction to the book! I would have made it differently today…

Include central methods • Present book: I do not show the central method in the strategy  calculateTime() I should have. Do it in your hand-ins! AU CS Henrik Bærbak Christensen 3

Inner and Outer Encapsulation

How do I? • Switch from channel TV2 to DR on my Samsung TV set? • A) Push the Button ‘3’ on the TV’s remote control interface? • B) Call Samsung to tell them to send a man to re-solder the wire inside the TV set? • Some of you accidentally use method B CS@AU Henrik Bærbak Christensen 5

Example • What happens when I want a WorldWar II HotCiv? – I have to call you guys to resolder the wires inside! AU CS Henrik Bærbak Christensen 6

Frameworks • What is the process in the mandatory exercises? – To use TDD and compositional design to transform an AlphaCiv application into a HotCiv framework • Frameworks are – Reusable software designs and implementations – Must be reconfigurable from the outside • Just like a TV set • Example – Android Google’s smartphone OS – You do not call Google to make them rewrite their constructor in order to introduce the App for your HCI course, do you!?! CS@AU Henrik Bærbak Christensen 7

Open/Closed • Open for Extension (I can adapt the framework) • Closed for Modification (But I cannot rewrite the code) • Change by addition, not by modification • So – public GameImpl(String whichVariant) { • If (whichVariant.equals (”Alpha”)) { – ageStrategy = new AlphaAgeStrategy() • Is not suitable for implementing frameworks… – I have to open the TV to solder the wires inside  – You have to call Google to make your HCI project app  CS@AU Henrik Bærbak Christensen 8

So… • Keep GameImpl, UnitImpl, CityImpl , … closed for modification! – They form the framework that is reused as-is • Allow adapting HotCiv to a WWII scenario by addition – I can code a WorldLayoutStrategy that produce a Europe map – Etc. – And provide my strategies in the constructor of your GameImpl – And it will do the right thing… CS@AU Henrik Bærbak Christensen 9

Uncle Bob??? • What about Uncle Bob? – Though shall not have more than two parameters as arguments • Disobey him for now… – GameImpl(AgeStrategy ageStrategy , …………………..) • We will refactor HotCiv soon enough to fix it… – Abstract Factory… AU CS Henrik Bærbak Christensen 10

Apropos Defining Worlds

Many like my ‘StubGame’ • … but be careful • If you interpret the datastructure in the GameImpl constructor you have a tile type switch inside the GameImpl – Then how to you make a Dune Game • Tile types ala ‘desert’ and ‘oasis’ ? AU CS Henrik Bærbak Christensen 12

Data driven configuration • However, the idea to keep configuration in datastructures is a good one… – Much better than tedious code ala ‘setTile(0,0, plain) – Easy to write a load from disk version AU CS Henrik Bærbak Christensen 13

You Can Do More Outside Inner and Outer have different Rules! AU CS Henrik Bærbak Christensen 14

Parametric Variant • Example: – GammaCiv requirement: Settlers make cities, archers fortify Coded by switching within HotCiv Framework GameImpl Code: GameImpl, CityImpl, UnitImpl, … AU CS Henrik Bærbak Christensen 15

Parametric Variant • Example: – GammaCiv: Settlers make cities, archers fortify Liability: HotCiv has hard bindings to specific HotCiv Framework unit types. Only Change by Modification! Code: GameImpl, CityImpl, UnitImpl, … AU CS Henrik Bærbak Christensen 16

All is Shit Variant • Example: – GammaCiv: Settlers make cities, archers fortify GammaCiv Delegates HotCiv Framework Code: GameImpl, CityImpl, UnitActionStrategy UnitImpl, … AU CS Henrik Bærbak Christensen 17

All is Shit Variant • Example: – GammaCiv: Settlers make cities, archers fortify REALLY BAD: If you have unit-type switching code in GameImpl, you GammaCiv Delegates still have a parametric solution with all its liabilities!!! HotCiv Framework Plus all the extra interfaces of the Code: compositional approach. GameImpl, CityImpl, UnitActionStrategy DO THE SAME THING UnitImpl, … THE SAME WAY!!! AU CS Henrik Bærbak Christensen 18

Compositional Variant • Example: – GammaCiv: Settlers make cities, archers fortify GammaCiv Delegates HotCiv Framework Code: Gamma GameImpl, CityImpl, UnitActionStrategy UnitImpl, … AU CS Henrik Bærbak Christensen 19

Compositional Variant • Example: – GammaCiv: Settlers make cities, archers fortify GammaCiv Delegates HotCiv Framework What would Henrik say? Is this Code: Gamma GameImpl, CityImpl, Parametric design??? UnitActionStrategy UnitImpl, … AU CS Henrik Bærbak Christensen 20

Compositional Variant • Example: – GammaCiv: Settlers make cities, archers fortify GammaCiv Delegates This is a much better design! (My own solution) Why? HotCiv Framework Because a) No hard binding in GameImpl b) Code: GammaCiv requirements are expressed Gamma GameImpl, CityImpl, explicitly in a single piece of code that bears the UnitActionStrategy UnitImpl, … correct name! AU CS Henrik Bærbak Christensen 21

Inner and Outer • Keep inner code (framework code) clean of variability switching code; have it in the outer code (delegates)! GammaCiv Delegates HotCiv Framework Code: UnitActionStrategy GameImpl, CityImpl, UnitImpl, … AU CS Henrik Bærbak Christensen 22

Inner and Outer • Keep inner code (framework code) clean of variability switching code; have it in the outer code (delegates)! HCI Course OurSuperHCIApp Android Framework AU CS Henrik Bærbak Christensen 23

Inner Outer Collaboration Delegates have to tell something

But what then… • GammaCivUnitStrategy has to – create a City??? – destroy a unit??? • Collaborate via well defined, descriptively named, protocol… • Do not reach into actual datastructures! – Breaks encapsulation… AU CS Henrik Bærbak Christensen 25

Lowering Bindings • True, the downside of using GameImp directly… – As in ‘g.removeUnitAt()’ • … is tight coupling from strategies onto implementation of Game  AU CS Henrik Bærbak Christensen 26

But we can… • Decouple through Interfaces, of course – Interface segregation principle or role interfaces • That is – <<interface>> Game As you know it – <<interface>> ModifiableGame extends Game • void createCityAt(…); • void removeUnitAt(…); • Then GameImpl implements ModifiableGame – And Strategy methods refer to instance of ModifiableGame • Exercise: – Why do we achieve lower bindings using this technique? AU CS Henrik Bærbak Christensen 27

The TradeOff • The benefit – Decoupling / lower coupling between Game and Strategies • The liability – More interfaces to overview • The balance is… – Do we need it? • Yes: Do it • No: KISS – keep it simple, stupid – And refactor when need arises AU CS Henrik Bærbak Christensen 28

Generalization or Specialization? Generalization is not a bad thing…

When Need Arise… • Agile development tells us – You ain’t gonna need it – Simplicity • That is: ”Do not generalize (= complicate) design if there is not use of it” • But do it when need arise… – Triangulation: Add tests that force generalization into existence. • Example: – Archers need to fortify in GammaCiv – Question: Is this a general feature or highly GammaCiv specific? AU CS Henrik Bærbak Christensen 30

Generalize • Fortify = unit is not moveable + defense strength change • Making units non-moveable sounds general to me… – Add accessor to interface ‘ isMoveable ()’ – Add mutator to implementing class ‘ setMoveable(boolean m)’ • Extra clause in the bail out fast of ‘ moveUnit(f,t )’ – boolean isMoveable = getUnit(f).isMoveable(); – if (! isMoveable) return false; AU CS Henrik Bærbak Christensen 31

But what about Legion/Settler • They then have this ‘isMoveable’ attribute also… • But they just never use it – And so? AU CS Henrik Bærbak Christensen 32

Multi Role’d Abstractions Big Ball of Mud Strategy Blob Strategy Multi-dimensional Variance

Consider… • One Strategy to Rule Them All! What is the problem? AU CS Henrik Bærbak Christensen 34

The Problem • ZetaCiv – I want to WinnerStrategy to be a combination of those of BetaCiv and EpsilonCiv – ZetaCivVariantStrategy extends BetaCivVariant and EpsilonCiv • Actually, it is the main discussion in the State Chapter in FRS and the State Pattern lecture ☺ , Stay tuned… AU CS Henrik Bærbak Christensen 35

Storing State Who knows how old the game is?

State in Strategies? • Game age state can be stored in – Game: • Keep track of how many rounds have been played – AgeStrategy: • Ok, some suggested keeping state (age) only here… • Strategy pattern is about algorithms – Algorithms compute stuff, they do (generally) not know stuff… • I may change the algorithm Cohesion again! Keep the state – Change the strategy at runtime in the object where is belongs AU CS Henrik Bærbak Christensen 37