This document discusses common design patterns and SOLID principles. It provides code examples and analysis of the Single Responsibility Principle, Open Closed Principle, Liskov Substitution Principle, Interface Segregation Principle, and Dependency Inversion Principle. It also summarizes the Factory Method, Strategy, Abstract Factory, and Bridge design patterns and analyzes how they relate to the SOLID principles.

1. Common Design Patterns
Session on Java - 4

2. Agenda
● SOLID principles with code examples.
● A look at a few Design Patterns with code examples + analysis from the
SOLID principles perspective.
SOLID principles are the meta-level principles. DPs are more concrete.

3. S - Single Responsibility Principle

4. S - Single Responsibility Principle (contd)
Formally-
A class or module should have one, and only one, reason to be changed.

5. S - Single Responsibility Principle (contd)
Code example.

6. What is the trade-off here?
What is a responsibility?
How do we decide upon “the single responsibility” of an entity?
S - Single Responsibility Principle (contd)

7. O - Open Closed Principle

8. O - Open Closed Principle (contd)
Formally-
Software entities (classes, modules, functions, etc) should be open for extension,
but closed for modification.

9. O - Open Closed Principle (contd)
Code example.

10. O - Open Closed Principle (contd)
Can we follow OCP 100%?
If not, any examples?

11. Liskov Substitution Principle

12. Liskov Substitution Principle (contd)
Formally-
Objects should be replaceable with instances of their subtypes without altering the
correctness of that program.

13. Liskov Substitution Principle (contd)
Code example.

14. Liskov Substitution Principle (contd)
What is a pre condition and what is a post condition?
What should be the restrictions on these?
Opinions about inheritance?

15. Interface Segregation Principle

16. Formally-
Clients should not be forced to depend on methods that they do not use.
Interface Segregation Principle (contd)

17. Code example.
Interface Segregation Principle (contd)

18. Interface Segregation Principle (contd)
Are the SRP and the ISP same?
Any examples where they could differ?
Is violation of one more dangerous than the other?

19. D - Dependency Inversion

20. Code example.
D - Dependency Inversion (contd)

21. Formally-
1. High level modules should not depend upon low level modules. Both
should depend upon abstractions.
2. Abstractions should not depend upon details. Details should depend upon
abstractions.
D - Dependency Inversion (contd)

22. D - Dependency Inversion (contd)
What is a DIC?
How does it work?

23. Design Patterns

24. Factory Method

25. Factory Method (contd)
Code example.

26. Does the Factory Method violate the Open Closed Principle?
Which SOLID principles are demonstrated by this pattern?
Factory Method (contd)

27. Strategy Pattern

28. Strategy Pattern (contd)
Code example.

29. Strategy Pattern (contd)
Which SOLID principles are demonstrated by this pattern?

30. Abstract Factory

31. Code example.
Abstract Factory (contd)

32. Which other design patterns do you see in this pattern?
Which SOLID principles are demonstrated by this pattern?
Abstract Factory (contd)

33. Bridge Pattern

34. Bridge Pattern (contd)
Code example.

35. Bridge Pattern (contd)
Which SOLID principles are demonstrated by this pattern?