SOLID principles and design patterns

Question 1

What are the 4 main features of OOP?

Answer 1

• Abstraction
• Encapsulation
• Inheritance
• Polymorphism

Question 2

What are design patters?

Answer 2

Not solutions but more principles, ideas or descriptions of how some code should function to implement the ‘pattern’.

Question 3

What are the three common types of design patterns?

Answer 3

1. Creational patterns
2. Structural patterns
3. Behavioural patterns

Question 4

What are creational patterns?

Answer 4

Concerned with creating objects as needed for the problem/situation faced.

Question 5

What are structural patterns?

Answer 5

Concerned with describing the relationships among objects.

Question 6

What are behavioural patterns?

Answer 6

Concerned with communication among objects.

Question 7

What are the SOLID principles?

Answer 7

• Single-responsibility principle
• Open-closed principle
• Liskov substitution principle
• Interface segregation principle
• Dependency inversion principle

Question 8

What is a short definition for Single-responsibility principle?

Answer 8

A class should only have a single responsibility.

Question 9

What is a short definition for open-closed princple?

Answer 9

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

Question 10

What is a short definition for Liskov substitution principle?

Answer 10

Objects should be replaceable with instances of their subtypes without altering the correctness of that program.

Question 11

What is a short definition for interface segregation principle?

Answer 11

Many client-specific interfaces are better than one general-purpose interface.

Question 12

What is a short definition for dependency inversion principle?

Answer 12

Depend on abstractions and interfaces, not concrete objects

Question 13

What is the explanation for Single-Responsibility Principle?

Answer 13

Concerns should be separated. Every class should be focused solely on one activity only, and the only reason to change it should be because that activity changes (excluding bug fixes)

Question 14

Consider this example: You have a single class that is responsible for requesting data from a remote system and generating reports. When might you rewrite the code according to the Single-Responsibility Principle.

Answer 14

• if the remote system changes
• if the report format changes

Question 15

Provide an explanation for the Open-Closed principle:

Answer 15

Software entities (class, modules, functions) should be open for extension but closed for modification.
Closed in the sense that it has a fixed API others can depend on.
Open in the sense that a component can be extended.

Question 16

Provide an explanation for the Liskov Substitution Principle (LSP)

Answer 16

In a subtype relationship, a derived class should be substitutable with any of its base class.

Question 17

Provide an explanation for Interface Segregation Principle:

Answer 17

Develop many specific interfaces (virtual classes in C++) for each specific concern rather than grouping them into homogenous blocks.

Question 18

What does the interface segregation principle promote?

Answer 18

• Modularity
• Reduced coupling
• Extensibility

Question 19

Provide an explanation for the dependency inversion principle:

Answer 19

High level classes do not depend upon low level classes. They depend upon abstractions. Abstractions do not depend upon details; details depend upon abstractions.

Question 20

What is the builder design pattern?

Answer 20

A design for constructing complex objects step by step.

Question 21

What does the builder design pattern help?

Answer 21

Helps separate construction of an object from its representation.

Question 22

What does the builder pattern do?

Answer 22

Designing our code in a certain way to encourage the use of classes. Rather than expose the construction of our complex classes we abstract it.

Question 23

What is the Singleton pattern?

Answer 23

The idea that there can only be one instance of class.

Question 24

What SOLID rule does the Singleton pattern violate?

Answer 24

The single Responsibility Principle. Singleton instances do something and control their own lifecycle.