L7: Making Software Reusable

Question 1

What is a “type”?

Answer 1

• Primitive types are variables that store actual values
• Reference types store references to an object T

Question 2

Abstract classes versus interfaces

Answer 2

Neither can be instantiated as object, both can specify behaviour and data

An interface is a collection of behaviour offered by an object of that type:
- Methods are defined but empty, all of them must be implemented in the class
- A class can implement multiple interfaces, since interfaces are not inheritance

An abstract class is abstracted behaviour of a collection of classes:
- Methods can be abstract (no implementation) or concrete (with implementation)
- Are (should be) part of an inheritance structure

Question 3

Enumeration (enums)

Answer 3

• Set of fixed values/constants
• Can be used in switches, loops, …
• Can also involve methods

Question 4

Record

Answer 4

Designed to store fixed values
Automatically have:
- Private field for each component
- Public getter
- Public constructor
- Implemented toString() method

Question 5

SOLID

Answer 5

• Single responsibility: each unit (class) should have only one responsibility
• Open/closed: units should be open for extensions, but closed for modifications
• Liskov substitution: methods that use references to classes must be able to use objects of derived classes (i.e. subclasses) without knowing it
• Interface segregation: no code should be required to rely on methods it is not using
• Dependency inversion: higher-level units should not depend on lower-level units, and both should depend on abstractions

Question 6

KISS: Keep It Simple, Silly!

Answer 6

It does not help to have a complicated solution nobody understands

Simpler solutions are less error-prone