SOLID Principles

Question 1

SOLID - S

Answer 1

Single Responsibility Principle

Question 2

Main idea of Single Responsibility Principle

Answer 2

A class should have just one reason to change.

Question 3

SOLID - O

Answer 3

Open / Closed Principle

Question 4

Main idea of Open / Closed Principle

Answer 4

Classes should be open for extension but closed for modification.

Question 5

SOLID - L

Answer 5

Liskov Substitution Principle

Question 6

Main idea of Liskov Substitution Principle

Answer 6

When extending a class, remember that you should be
able to pass objects of the subclass in place of objects of
the parent class without breaking the client code.

Question 7

What means Liskov Substistution Principle

Answer 7

This means that the subclass should remain compatible with
the behavior of the superclass. When overriding a method,
extend the base behavior rather than replacing it with some-
thing else entirely.

Question 8

What Liskov Substitution Principle states about method parameters

Answer 8

Parameter types in a method of a subclass should match or be
more abstract than parameter types in the method of the super-
class

Question 9

What Liskov Substitution Princliple states about method return types

Answer 9

The return type in a method of a subclass should match or be
a subtype of the return type in the method of the superclass

Question 10

What Liskov Substitution Principle states about throwning exceptions

Answer 10

A method in a subclass shouldn’t throw types of exceptions
which the base method isn’t expected to throw

Question 11

What Liskov Substitution Principle states about pre-conditions

Answer 11

A subclass shouldn’t strengthen pre-conditions

Question 12

What Liskov Substitution Principle states about post-conditions

Answer 12

A subclass shouldn’t weaken post-conditions

Question 13

What Liskov Substitution Principle states about invariants

Answer 13

Invariants of a superclass must be preserved

Question 14

What Liskov Substitution Principle states about private fields

Answer 14

A subclass shouldn’t change values of private fields of the
superclass

Question 15

SOLID - I

Answer 15

Interface Segregation Principle

Question 16

Main idea of Inteface Segregation Principle

Answer 16

Clients shouldn’t be forced to depend on methods they do not use (interface should be as narrow as possible)

Question 17

SOLID - D

Answer 17

Dependency Inversion Principle

Question 18

Main idea of Dependency Inversion Principle

Answer 18

High-level classes shouldn’t depend on low-level class-es. Both should depend on abstractions. Abstractions
shouldn’t depend on details. Details should depend on abstractions.

Question 19

What is low-level class?

Answer 19

Implement basic operations such as working with a disk, transferring data over a network, connecting to a
database

Question 20

What is high-level class?

Answer 20

Contain complex business logic that directs low-level classes to do something

Question 21

What is an object invariants

Answer 21

Invariants are conditions in which an object makes sense. They can be defined explicitly in the form of interface contracts or a set of assertions within methods, they could also be implied by certain unit tests and expectations of the client code.
For example, invariants of a cat are having four legs, a tail, ability to meow.