The document discusses the SOLID principles of object-oriented design: 1. Single Responsibility Principle (SRP) states that a class should have one and only one responsibility. Having multiple capabilities in a class makes the code difficult to maintain. 2. Open-Closed Principle (OCP) states that a class should be open for extension but closed for modification. New features can be added by inheriting from the class or extending its behavior without changing the original code. 3. Liskov Substitution Principle (LSP) states that subclasses should not break the behavior of the parent class and any program using the parent class should work the same way if the parent is substituted with the child

1. SOLID Principles

2. 1. Single Responsibility Principle
(SRP)
 According to the single responsibility
principle, each Java class must perform only
one function.
 Multiple capabilities in a single class mashup
the code, and any changes made to the code
may influence the entire class.
 It specifies the code and makes it simple to
maintain.

4. Example of code before
implementing SRP:

5. Example of code after implementing
SRP:

6. Think about this example

7. If you have the following code for
school management, How would
you refactor the class to adhere to
SRP?

8. Answer:

9. 2. Open-Closed Principle
 The Open-Closed Principle (OCP) states that a
class should be open for extension but closed for
modification. This means that the behavior of a class
can be extended without modifying its source code. In
other words, you can add new features to the class
without changing its existing behavior.
 Extending the class can be done in a variety of ways,
including,
• Inheriting from class.
• Overwriting the required behavior from the class.
• Extending certain behavior of the class.

11. Example of code before
implementing OCP:

12. Example of code after implementing
OCP:

13. Think about this example

14. If you have the following code for
payment processor, How can you
redesign the PaymentProcessor
class to follow the OCP?

16. Answer:

17. Answer:

18. 3. Liskov Substitution Principle
(LSP)
 The LSP states that if a program is using a base
class (Like Interface), it should be able to use
any of its derived classes (Inherited Classes)
without knowing it. In other words, a derived class
should be able to substitute for its base class
without changing the behavior of the program.
 When a class is a subtype of another class, it
means that it inherits the behavior and properties
of the base class.
 However, if the derived class has different
behavior or properties than the base class, it can
cause unexpected behavior in the program.

20. Example of code before
implementing LSP:

21. Example of code after implementing
LSP:

22. Another answer:

23. Think about this example

24. Consider a class hierarchy where a
Bird class has a method fly(). You
have subclasses such as Sparrow
and Ostrich inheriting from Bird.
Given that not all birds can fly (e.g.,
ostriches cannot fly), how does this
design violate the Liskov
Substitution Principle? Propose a
solution to rectify this issue.

26. Answer:

27. 4. Interface Segregation Principle
 The Interface Segregation Principle (ISP) is a
principle in object-oriented programming that
states that a client should not be forced to
depend on methods it does not use.
 the Interface Segregation Principle (ISP) is a
principle in object-oriented programming that
states that a client should not be forced to
depend on methods it does not use.

29. Example of code before
implementing ISP:

31. Example of code after implementing
ISP:

32. Think about this example

33. •A SmartDevice interface includes
methods for functionalities like
calling, browsing the internet, and
taking photos. Some devices, like
smart cameras, only need the photo-
taking capability. Explain how the
current design violates the Interface
Segregation Principle and suggest a
way to redesign the interface(s) to
resolve this violation.

34. Answer

35. Answer

36. For more details about SOLID principles
https://everyone-can-
code.github.io/solid/srp/https://everyone-
can-code.github.io/solid/srp/
Thank You.