COURS 1 : SOLID

Question 1

What are the Patterns, Principles

and Best practices of solid?

Answer 1

• To deliver faster
• To manage change
• To manage complexity

Question 2

What are the principles of Solid?

Answer 2

• A class needs to have a single responsibility
• GRASP PRINCIPLE :  High cohesion The methods of a class use a lot of the other members of the same class.
• GRASP PRINCPLE :Low coupling :The methods of a class do not use many members from other classes.
 High cohesion + Low coupling → Less responsibilities, less reasons to
change.
• So, maintain the cohesion and the coupling of the class!

Question 3

What do we mean when we say “Open-chest surgery isn’t needed when putting on a coat.”?

Answer 3

• The software entities need to be open to extensions, but close to modifications.
• Always think: “what will happen if the entity changes?”

Question 4

Define the Liskov principle.

Answer 4

• The functions that use references to base classes must be able to use objects of the derived classes without knowing.
• The preconditions cannot be enforced in the derived type. The derived methods cannot expect more than the base methods.
• The postconditions cannot be more relaxed in the derived type. The derived methods cannot provide less than the base methods.

Question 5

What is the interface segregation principle?

Answer 5

Multiple interfaces specific to clients are worth more than a single interface.

Question 6

What is the dependency inverion principle?

Answer 6

• Depend on abstractions. Do not depend on concrete classes.
• The Holy Grail of software architecture!
• If we want to change the database, how many classes will we have to
change?
• If we depend on software libraries, our systems is locked within a
specific language (DIP violated).
• If we depend on REST APIs, our system remains independent of languages (DIP guaranteed).