Introduction to Scala

Question 1

What is Scala?

Answer 1

Scala is a general-purpose programming language providing support for functional programming and a strong static type system. Designed to be concise, many of Scala’s design decisions aimed to address criticisms of Java.

Question 2

What language does Scala compile in?

Answer 2

Scala source code is intended to be compiled to Java bytecode, so that the resulting executable code runs on a Java virtual machine.

Question 3

What does Scala stand for?

Answer 3

Scalable Language

Question 4

Which companies use Scala?

Answer 4

Netflix, Morgan Stanley, Airbnb, Deutsche Bank

Question 5

Why is Scala flexible?

Answer 5

Scala lets you add new types, collections and control constructs that fee llike they are built-in to the language.

Question 6

Why is Scala convenient?

Answer 6

The Scala standard library has a set of convenient predefined types, collections and control constructs.

Question 7

Who uses Scala?

Answer 7

Software Engineers, Data Engineers, Data Scientists, Machine Learning Engineers

Question 8

Which framework is written in Scala?

Answer 8

Apache Spark

Question 9

Whichi programming paradigms does Scala fuse?

Answer 9

Object-oriented and functional

Question 10

What makes Scala scalable?

Answer 10

The fusion of object-oriented and functional paradigms.

Question 11

Why is Scala an object-oriented programming language?

Answer 11

Every value is an object and every operation is a method call.

Question 12

Why is Scala a functional programming language?

Answer 12

Functions are first-class values: you can pass them as argument to functions, return them from functions, store them in variables…

Operations of a program should map input values to output values rather than change data in place. In other words, functions should not have side effects.

Question 13

Why use Scala?

Answer 13

Scala is scalable, concise, high-level, static, compatible with Java.

Question 14

Which command lets you start the Scala interpreter?

Answer 14

scala

Question 15

Which function lets you print values to standard output?

Answer 15

println(value)

Question 16

What are the two kinds of variables Scala offers?

Answer 16

val and var

Question 17

What distinguishes val variables?

Answer 17

val variables are immutable. They can’t be reassigned,

Question 18

How do you declare an immutable integer variable in Scala?

Answer 18

val variableName: Int = 10

Question 19

How do you declare an immutable string in Scala?

Answer 19

val variableName: String = “Alex”

Question 20

What distinguishes var variables?

Answer 20

var variables are mutable. They can be reassigned.

Question 21

How do you declare a mutable integer in Scala?

Answer 21

var variableName: Int = 1

Question 22

How do you declare a mutable string in Scala?

Answer 22

var variableName: String = “Alex”

Question 23

Why should you prefer vals over vars?

Answer 23

• Your data won’t be changed inadvertently (defensive programming).
• Your code is easier to reason about.
• You have to write fewer tests.

Question 24

What is the main drawback of immutability?

Answer 24

More memory is needed due to data copying.

Question 25

Which command lets you execute a Scala script?

Answer 25

scala script.scala

Question 26

How do you write comments in Scala?

Answer 26

// Comment

Question 27

How does an interpreted language work?

Answer 27

With an interpreated language, the program directly executes instructions written in a programming language, without requiring them previously to have been compiled into machine code.

Question 28

How does a compiled language work?

Answer 28

With a compiled language, a program translates source code from a high-level programming language to a lower level language (e.g., machine code) to create an executable program.

Question 29

How do Scala applications differ from Scala scripts?

Answer 29

• They need to be compiled explicitly and then run explicitly.
• They consist of many source files than can be compile individually.
• They are useful for larger programs.
• There’s no lag time since applications are precompiled.

Question 30

Which command lets you translate Scala code to Java bytecode?

Answer 30

scalac App.scala

Question 31

What are the advantage and inconvenient of a compiled language?

Answer 31

• Advantage: Increased performance once compiled.
• Disadvantage: It takes time to compile code.

Question 32

How do you define a function in Scala?

Answer 32

def bust(hand: Int): Boolean = {
 hand \> 21
}

The function’s body follows the = sign and is written within {}.

”: Boolean = “ is optional and can be removed.

Question 33

How do you create an immutable array in Scala?

Answer 33

val players = Array(“Alex”, “Chen”, “Marta”)

Question 34

How do you parameterize an array in Scala?

Answer 34

val players: Array[String] = new ArrayString

to create an array holding 3 strings.

The type parameter is part of the instance; the value parameter is not.

Question 35

How do you intialize elements of an array in Scala?

Answer 35

players(0) = “Alex”

Indexing is done using parentheses (), not square brackets like in Java and Python.

Question 36

What is the difference between arrays and lists in Scala?

Answer 36

Arrays are mutable (you can add or replace elements as long as they are the same type), lists are immutable.

Question 37

How do you create a list in Scala?

Answer 37

val players = List(“Alex”, “Chen”, “Marta”)

Question 38

How do you prepend an element to a list in Scala?

Answer 38

val newPlayers = “Sindhu” :: players

or define players as a var, and use:

var players = “Sindhu” :: players

Question 39

What are :: in Scala?

Answer 39

Cons.

Question 40

How do you specify an empty list in Scala?

Answer 40

Nil

Question 41

How do you prepend an element to a list?

Answer 41

element :: list

Question 42

How do you concatenate lists in Scala?

Answer 42

list1 ::: list2

Question 43

What are some advantages of static type systems?

Answer 43

• Increased performance at run time
• Properties of your program verified (absnece of common type-related bugs)
• Safe refactorings
• Explicit documentations with type annotation
  *

Question 44

What are some inconvenients of static type systems?

Answer 44

• Delay before execution (takes time to check types)
• Code is verbose (longer to write)
• Language is not flexible (one strict way of composing a type)

Question 45

How do you create an if statement in Scala?

Answer 45

if (hand > 21) {
println(“This hand busts!”)
}

Curly braces are a style guide recommendation.

Question 46

How do you create an if else statement in Scala?

Answer 46

if (handA > handB)
println(handA)
else
println(handB)

The bodies can be put on the same line if they are just one line of code. No curly braces are necessary.

Question 47

How do you define a while loop in Scala?

Answer 47

while (i < repetitions) {
body
}

Question 48

Why can Scala be imperative?

Answer 48

Scala can be imperative because:

• It can execute one command at a time
• It can iterate with loops
• It can mutate shared states (variables out of scope)

Question 49

Which Scala method lets you loop over a variable and apply a function to its elements?

Answer 49

variable.foreach(function)

Question 50

In computer science, what is a side effect?

Answer 50

A side effect happens when code modifies some variable outside of its local scope. Printing to the standard output stream is a side effect.

Question 51

In Scala, what are some signs of the imperative style?

Answer 51

• var
• side effect
• Unit

Question 52

In Scala, what are some signs of the functional style?

Answer 52

• val
• no side effects
• Non-Unit value types
  
  • Int
  • Boolean
  • Double

Question 53

What are some benefits of the functional style?

Answer 53

• Your data won’t be changed inadvertently
• Your code is easier to reason about
• You have to write fewer tests
• Functions are more reliable and reusable

Question 54

In Scala, should you prefer the functional or the imperative style?

Answer 54

You should use the functional style at first instinct, and then use the imperative style if the need arises.