SOLID Principles Design Patterns and Principles Part 3

Question 1

is a mnemonic for five design principles intended to make
software designs more understandable, flexible and maintainable.

Answer 1

SOLID

Question 2

introduced them in the book Agile Software Development, Principles, Patterns, and Practices

Answer 2

Robert Martin

Question 3

● A class should have just one reason to change.
● The main goal of this principle is reducing complexity

Answer 3

Single Responsibility Principle

Question 4

● Classes should be open for extension but closed for
modification.
● The main idea of this principle is to keep existing code
from breaking when implementing new features.

Answer 4

Open/Closed Principle

Question 5

A class is __ if you can extend it, produce a subclass
and do whatever you want with it add new methods
or fields, override base behavior, etc.

Answer 5

open

Question 6

A class is __ (or complete ) if it’s 100% ready to be
used by other classes its interface is clearly defined
and won’t be changed in the future.

Answer 6

closed

Question 7

● 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.
● This means that the subclass should remain compatible with the
behavior of the superclass.

Answer 7

Liskov Substitution Principle

Question 8

Liskov
Substitution Principle is named by ___ , who defined it in 1987 in
her work Data abstraction and hierarchy

Answer 8

Barbara Liskov

Question 9

The substitution principle has a set of formal
requirements for subclasses , and specifically for
their methods, which are as follows:

Answer 9

1. Parameter types in a method of a
   subclass should match or be more abstract
   than parameter types in the method of the
   superclass.
2. 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.
3. A method in a subclass
   shouldn’t throw types of
   exceptions which the base method isn’t expected to
   throw.
4. A subclass shouldn’t strengthen pre
   conditions.
5. A subclass shouldn’t weaken post
   conditions.
6. Invariants of a superclass must be preserved.
7. A subclass shouldn’t change values of private fields of
   the superclass

Question 10

● Clients shouldn’t be forced to depend on
methods they do not use.
● Try to make your interfaces narrow enough
that client classes don’t have to implement
behaviors they don’t need.
● Clients should implement only those methods
that they really need. Otherwise, a change to
a “fat” interface would break even clients
that don’t use the changed methods.

Answer 10

Interface Segregation Principle

Question 11

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

Answer 11

Dependency Inversion Principle

Question 12

Usually when designing software, you can make a distinction
between two levels of classes.

Answer 12

Low level classes
High level classes

Question 13

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

Answer 13

Low level classes

Question 14

contain complex business logic
that directs low level classes to do something.

Answer 14

High level classes

Question 15

The dependency inversion principle suggests changing the direction of this
dependency by:

Answer 15

■ Describe interfaces for low level operations that high level classes rely on,
preferably in business terms.
■ Make high level classes dependent on those interfaces, instead of on
concrete low level classes.
■ Once low level classes implement these interfaces, they become
dependent on the business logic level