Object-Oriented Programming in Swift

Question 1

What is another word for an object?

Answer 1

Class instances

Question 2

What are objects?

Answer 2

Self-contained modules of functionality that can be easily used and re-used as the building blocks of a software application.

Question 3

Instances consist of 1. _____ _____ called _____ and 2. _____ called ______. They can be accessed and called on the instance to perform tasks AND are collectively referred to as 3. _______ _______.

Answer 3

1. Data variables, properties
2. Functions, methods
3. Class members

Question 4

What does a class do? Specify

Answer 4

Defines what an instance will look like when it’s created. What methods will do and what properties will be.

Question 5

What does the “properties” section of a class do?

Answer 5

Defines the variables and constants to be contained in the class.

Question 6

What is the idea behind “data encapsulation”?

Answer 6

Data should be stored within classes and accessed only through methods defined in that class.

Question 7

Data encapsulated in a class is referred to as _______ and _____

Answer 7

Properties, Instance variables

Question 8

What’s the difference between a type method and an instance method?

Answer 8

1. A type method operates at the level of a class, such as creating a new instance of a class.
2. An instance method operates only on an instance of a class such as performing an arithmetic operation on two properties and returning the result.

Question 9

Where and how is an instance method declared?

Answer 9

Within the opening and closing braces of the class to which it belongs using the standard Swift function declaration syntax.

Question 10

How is a type method declared?

Answer 10

By preceding the declaration with the “class” keyword.

Question 11

syntax to create an instance of a class

Answer 11

var instanceName: ClassName = ClassName( )

Question 12

What does dot notation do?

Answer 12

Calls instance methods and accesses properties built into a class.

Question 13

Syntax to access an instance variable or call an instance method?

Answer 13

classInstanceName.propertyName
Or
classInstanceName.instanceMethod( )

Question 14

What are the two class property categories?

Answer 14

“Stored properties” and “computed properties”

Question 15

What is a “computed property”?

Answer 15

A property that’s derived based on some form of calculation or logic at the point at which the property is set or retrieved.

Question 16

How are “computed properties” implemented?

Answer 16

By creating “getter” and optional “setter” methods containing the code to perform the computation.

Question 17

1. What’s unique about a property being declared as “lazy”?

2. How is this advantageous?

Answer 17

1. It will only be initialized when it’s first accessed.

2. It allows resource intensive activities to be deferred until the property is needed.

Question 18

Lazy properties must be declared as ______.

Answer 18

variables (var)

Question 19

Why prefix references to properties and methods with the self property?

Answer 19

To indicate that the method or property belongs to the current class instance.

Question 20

Why is it no longer necessary to use self in most situations?

Answer 20

It’s now assumed to be the default for references to properties and methods.

Question 21

What are two situations where it is still necessary to use the “self” property?

Answer 21

1. When referencing a property or method from within a closure expression.
2. When a function parameter has the same name as a class property.

Question 22

Define protocol

Answer 22

A keyword that specifies the methods and properties a class or struct must contain in order to be in conformance.

Question 23

What do “Opaque return types” do?

Answer 23

Allow a function to return any type as long as it conforms to a specified protocol.

Question 24

How are “opaque” return types declared?

Answer 24

By preceding the protocol name with the “some” keyword.

Question 25

What is a concrete type?

Answer 25

A specific return type.

Question 26

How do you create class hierarchy?

Answer 26

By deriving classes

Question 27

What is “single inheritance”?

Answer 27

The concept that a subclass can only be derived from a single direct parent class.

Question 28

What are the two rules that must be obeyed when overriding a method of a class?

Answer 28

1. The overriding method in the subclass must take exactly the same number and type of parameters as the overridden method in the parent class
2. The new method must have the same return type as the parent method.

Question 29

To avoid potential initialization problems, the init method of the _______ must always be called after the initialization tasks for the _______ have been completed.

Answer 29

superclass, subclass

Question 30

1. What is an “extension” used for?

2. What sort of features can an extension be used to add?

Answer 30

1. To add new functionality to a class without needing to create a subclass.
2. To add features such as methods, initializers, computed properties, and subscripts to an existing class without the need to create and reference a subclass.

Question 31

What are 3 things that structures have in common with classes?

Answer 31

1. They can be extended
2. They’re able to adopt protocols
3. They contain initializers

Question 32

What happens when a structure instance is copied?

Answer 32

The copy has its own version of the data which is unconnected with the original structure instance.

Question 33

What happens when a class instance is copied?

Answer 33

The only thing duplicated or passed is a reference to the location in memory where that class instance resides.

Question 34

Unlike classes structures can not contain a _____ method

Answer 34

de-initializer (deinit)

Question 35

Why are structures generally recommended whenever possible?

Answer 35

They are more efficient and safer to use in multi-threaded code then classes.

Question 36

In what three situations should classes be used over structures?

Answer 36

1. Inheritance is needed
2. Only one instance of the encapsulated data is required
3. Extra steps need to be taken to free up resources when an instance is de-initialized.

Question 37

1. What are enumerations?

2. When are they of particular use?

Answer 37

1. A data type of pre-defined sets of state values.

2. When identifying state within a switch statement.

Question 38

What do “property wrappers” do?

Answer 38

They allow the capabilities of computed properties to be separated from individual classes/structures and reused throughout the app code base.

Question 39

1. How are property wrappers declared?
2. Where are they implemented?
3. What is the preferred choice for implementation?

Answer 39

1. Using the @propertyWrapper directive
2. In a class or struct
3. Structures

Question 40

What are arrays and dictionaries in Swift?

Answer 40

Objects that contain collections of other objects

Question 41

What’s an array?

Answer 41

A data type that holds multiple values in a single ordered collection.

Question 42

Syntax to create and initialize a populated collection of array literal values

Answer 42

var variableName: [type] = [value 1, value2, value3, …….. ]

Question 43

The following syntax could be used to create an empty array

Answer 43

var arrName = [type] ( )