Applying software design principles in practice

How to apply design principles in practice?

Ganesh Samarthyam!Consultant, ZineMind LLC!ganesh.samarthyam@zinemind.com

“Applying design principles is the key to creating high-quality software!”

Architectural principles: !Axis, symmetry, rhythm, datum, hierarchy, transformation

Technology changes fast => FOMO

Often frustrating to develop quality software!

There must be a better way!“Here is Edward Bear,

coming downstairs now, bump, bump, bump,

on the back of his head, behind Christopher Robin.

It is, as far as ... !

It is, as far as he knows, the only way of coming downstairs,

but sometimes he feels that there really is another way,

if only he could stop bumping for a moment and think of it!”

!- A.A. Milne

Think, think, think!

Focus on software design is the key!

Real scenario #1Initial design

Real scenario #1

❖ How will you refactor such that:!

❖ A specific DES, AES, TDES, … can be “plugged” at runtime?!

❖ Reuse these algorithms in new contexts? !

❖ Easily add support for new algorithms in Encryption? !

Next change: smelly design

Time to refactor!Three strikes and you

refactor

Martin Fowler

Potential solution #1?Broken

hierarchy!

Yuck! !Your solution smells

Potential solution #2?Algorithms not

reusable!

Hmm, can be better. !Better luck next time…

Potential solution #3?

Wow!!What a nice solution :)

Can you identify the pattern?

You’re right: Its Strategy pattern!

Real scenario #2

Initial design

Real scenario #2

How to add support for new content types and/or algorithms?

Yuck! !This design smells

How about this solution?

Wow!!What a nice solution :)

Can you identify the pattern structure?

You’re right: Its Bridge pattern!

Wait, what principle did we apply?

Open Closed Principle (OCP)

Bertrand Meyer

Software entities should be open for extension, but closed for modification

Variation Encapsulation Principle (VEP)

Erich Gamma, Richard Helm, Ralph Johnson and John Vlissides

Encapsulate the concept that varies

Fundamental principle: Encapsulation

The principle of encapsulation advocates separation of concerns and!information hiding through techniques such as hiding implementation!

details of abstractions and hiding variations

Enabling techniques for encapsulation

Other fundamental principles?

Principles*

Abstrac/on*

Encapsula/on*

Modulariza/on*

Hierarchy*

Applying principles in practice

EncapsulationViolating!

encapsulationAdherence to !encapsulation

Applying !encapsulation

Applying principles in practice

PrincipleViolating!principles

Adherence to !principles

Refactoring

Bad design !(with smells)

Good design (with patterns)

Design determines qualities

Understandability Changeability Extensibility

Reusability Testability Reliability

DESIGNimpacts

impactsimpacts

“Applying design principles is the key to creating high-quality software!”

Architectural principles: !Axis, symmetry, rhythm, datum, hierarchy, transformation

Presentation sourceForewords by

Grady Booch and Dr. Stephane Ducasse

What are your takeaways?

Image/video credits❖ http://en.wikipedia.org/wiki/Fear_of_missing_out!❖ http://lesliejanemoran.blogspot.in/2010_05_01_archive.html!❖ http://javra.eu/wp-content/uploads/2013/07/angry_laptop2.jpg!❖ https://www.youtube.com/watch?v=5R8XHrfJkeg!❖ http://womenworld.org/image/052013/31/113745161.jpg!❖ http://www.fantom-xp.com/wallpapers/33/I'm_not_sure.jpg!❖ https://www.flickr.com/photos/31457017@N00/453784086 !❖ https://www.gradtouch.com/uploads/images/question3.jpg!❖ http://gurujohn.files.wordpress.com/2008/06/bookcover0001.jpg !❖ http://upload.wikimedia.org/wikipedia/commons/d/d5/Martin_Fowler_-_Swipe_Conference_2012.jpg!❖ http://www.codeproject.com/KB/architecture/csdespat_2/dpcs_br.gif !❖ http://upload.wikimedia.org/wikipedia/commons/thumb/2/28/Bertrand_Meyer_IMG_2481.jpg/440px-

Bertrand_Meyer_IMG_2481.jpg !❖ http://takeji-soft.up.n.seesaa.net/takeji-soft/image/GOF-OOPLSA-94-Color-75.jpg?d=a0 !❖ https://developer.apple.com/library/ios/documentation/cocoa/Conceptual/OOP_ObjC/Art/watchcalls_35.gif!❖ http://www.pluspack.com/files/billeder/Newsletter/25/takeaway_bag.png !❖ http://cdn1.tnwcdn.com/wp-content/blogs.dir/1/files/2013/03/design.jpg