SOLID

Question 1

What are the names of the 5 SOLID principles?

Answer 1

Single Responsibility
OPEN/CLOSED
Liskov Substitution
Interface Segregation
Dependency Inversion

Question 2

What is single responsibility?

Answer 2

A class should have one and only one reason to change, meaning that a class should have only one job. This means that a class should be extendable without modifying the class itself

Question 3

What is an issue with not following this principle?

Answer 3

Changes in one area can inadvertently affect other unrelated areas, a tightly coupled system that is hard to maintain.

Question 4

Example of Single Responsibility?

Answer 4

Report class has both a generateReport and sendReportByEmail methods. Now modifying the way reports are generated could unintentionally affect the email functionality
public class Report {
public void generateReport()
public void sendReportByEmail(String emailAddress)
}

Question 5

What is OPEN/CLOSED

Answer 5

Objects or entities should be open for extension but closed for modification

Question 6

What is an issue with not following this principle?

Answer 6

Modifying existing code can potentially cause new bugs in an otherwise happy application

Question 7

What is an exception to OPEN/CLOSED?

Answer 7

Fixing a bug in the existing code

Question 8

How does the Single Responsibility principle help us build better software?

Answer 8

Testing – A class with one responsibility will have far fewer test cases.

Lower coupling – Less functionality in a single class will have fewer dependencies.

Organization – Smaller, well-organized classes are easier to search than monolithic ones.

Question 9

What is the Liskov Substitution?

Answer 9

If class A is a subtype of class B, we should be able to replace B with A without disrupting the behavior of our program.

Example:
A Bird class with method of fly(). Introducing a sparrow and eagle subclass works fine but a penguin introduces a problem. To fix this we could introduce a more appropriate design such as separating flying and non-flying birds with an interface flyable so now a sparrow is a subclass of bird but implements flyable while a penguin does not.