Chapter 5 - Design Principles

Question 1

abstractions

Answer 1

a simplified representation of a given entity

Functions, classes, interfaces, and packages are classic abstractions provided by programming languages

Question 2

What is the primary objective of software design?

Answer 2

to decompose a problem into smaller parts

Question 3

design principles

Answer 3

guidelines for ensuring that a design meets the aforementioned properties

Question 4

design properties

Answer 4

conceptual integrity, information hiding, cohesion, and coupling

Question 5

Conceptual integrity

Answer 5

facilitates system usage and comprehension. When we follow this property, a user familiar with one part of a system feels comfortable using another part, as the features and user interface remain consistent.

Question 6

Information hiding

Answer 6

offers the following advantages to a software project: Parallel development, Changeability, Comprehensibility

Question 7

interface

Answer 7

class’s public members

Question 8

Cohesion

Answer 8

each class should fulfill a single function or service. Specifically, all methods and attributes of a class should contribute to the implementation of the same service

Question 9

Separation of concerns

Answer 9

recommends that a class should implement only one concern. In this context, concern refers to any functionality, requirement, or responsibility of the class.

Question 10

Coupling

Answer 10

the strength of the connection between two modules

Question 11

acceptable coupling

Answer 11

between class A and class B when:

1. Class A only uses public methods from class B.
2. The interface provided by B is stable, both syntactically and semantically. This means that the signatures of B’s public methods do not change frequently, and neither does the behavior of these methods. As a result, changes in B will rarely impact A.

Question 12

poor coupling

Answer 12

between class A and B when changes in B can easily impact A.

1. When classes A and B share global variables or data structures, for instance, when B changes the value of a global variable used by A.
2. When class A directly accesses a file or database used by class B.
3. When B’s interface is not stable. For example, when the public methods of B are frequently renamed.

Question 13

Structural Coupling

Answer 13

between A and B occurs when a class A has an explicit reference in its code to a class B.

For example, the coupling between ParkingLot and Hashtable is structural

Question 14

Evolutionary (or Logical) Coupling

Answer 14

between A and B occurs when changes in class B usually propagate to class A.

Thus, in Example 2, where class A depends on an integer stored in a file maintained by B, there is an evolutionary coupling between A and B. For instance, changes in the file format would have an impact on A.

Question 15

SOLID Principles

Answer 15

Single Responsibility Principle
Open Closed Principle
Liskov Substitution Principle
Interface Segregation Principle
Dependency Inversion Principle

Question 16

Single Responsibility Principle

Answer 16

This principle is an application of the idea of cohesion. It proposes that every class should have a single responsibility.

Question 17

presentation

Answer 17

a system should have presentation classes, which implement the interface with users

Question 18

business logic

Answer 18

classes perform computations directly related to the solution domain

Question 19

Interface Segregation Principle

Answer 19

The principle states that interfaces should be small, cohesive, and, more importantly, specific to each type of client. Its aim is to prevent clients from depending on interfaces with many methods they won’t use.

Question 20

Dependency Inversion Principle

Answer 20

This principle advocates that client classes should primarily depend on abstractions rather than on concrete implementations, as abstractions (i.e., interfaces) tend to be more stable than concrete implementations (i.e., classes).

Question 21

Prefer Composition Over Inheritance

Answer 21

the principle does not prohibit the use of inheritance. It merely suggests that when faced with two design solutions—one based on inheritance and the other on composition—the latter is generally preferable

Question 22

Class inheritance

Answer 22

(example: class A extends B) involves code reuse

Question 23

Interface inheritance

Answer 23

(example: interface I extends J) does not involve code reuse

Question 24

composition

Answer 24

exists when a class A contains an attribute whose type is another class B.

Question 25

Demeter Principle

Answer 25

asserts that a method’s implementation should only invoke methods:

From its own class (case 1)
From objects received as parameters (case 2)
From objects created by the method itself (case 3)
From attributes of the method’s class (case 4)

Question 26

Open-Closed Principle

Answer 26

core concept is that developers should not only implement a class, but also prepare it for future extensions and customizations. To achieve this, they can use parameters, inheritance, higher-order (or lambda) functions, and design patterns

Question 27

Liskov Substitution Principle

Answer 27

establishes rules for redefining methods in subclasses