Scala

Q1. Scala bytecode can run on top of Java VM. What is the fundamental difference between Java object.clone() and Scala object.copy()?

One is a Java object, the other is a Scala object.
clone() will copy class structures but not the data, while copy() will also copy data into new objects.
There is no difference.
copy() allows you to change values during the copying process; clone() does not.

Q2. What value does this code return?

val m1 = Map("a"->1,"b"->2,"c"->3)
m1("a")

a
2
b
1

Q3. What is one way to avoid low-level parallelization details?

monads
literal functions
partially applied functions
parallel collections

Q4. What do you use in ScalaTest to see a detailed diagram of error messages when a test fails?

ArgumentExceptions
AssertionException
DiagrammedAssertions
JUnit

Q5. What data type would you use to store an immutable collection of objects that contain a fixed number of varying types?

Array
ImmutableCollection
List
Tuple

Q6. After defining a function in the interpreter, Scala returns the following. What does the `()` indicate?

myfnc: ()Unit

The function has no side effects.
The function takes no parameters.
The function returns no value.
Returning unit types to the function is a closures.

Q7. What type of number is 1234.e5?

hexadecimal
short
floating point
long

Q8. When you convert a map to a list using the `toList` method of the map, the result will be of which type?

List[(String, String)]
List[(Array, Array)]
List[(Collection, Collection)]
List

Q9. What type of object does this code create?

val x = (1234, "Active")

List
Map
Tuple
Array

Q10. Which is a subclass of all classes?

AnyVal
AnyRef
Method
Null

Reference: Null in Scala Standard library. The question is a bit incorrect - Null is a subtype of every type except those of value classes

Q11. For the for-yield construct, is the scope separate between for-body and yield-body?

Yes and no. It is different depending on the for construct and what it does.
Yes, because the for section does not expose its scope.
No, because for-yield shares the same scope, even though they are within separate curly braces.
Yes, because they are within different curly braces.

Example: yield-body has access to the e variable from the for-body

val a = Array(1, 2, 3, 4, 5)
for {
     e <- a if e > 2
} yield e

Q12. What is one way to implement pattern matching on methods?

using regex
using monads
using string matching
using case classes

Note: ambiguous question, it's not clear what kind of pattern matching is meant here.

Q13. What is the value of z after executing this code?

val y = List('a','b')
val z = y::List('c')

List(a,b,c)
List(List(a, b), c)
List(c,a,b)
List(c,List(a,b))

Q14. What term is used to specify a precondition?

assert
require
precondition
mustHave

Q15. Which Scala type may throw an exception or a successfully computed value, and is commonly used to trap and propagate errors?

scala.util.ExceptionHandling
scala.Catch.Throw
scala.exception.TryFinally
scala.util.Try

Reference: scala.util.Try

Q16. What is the data type of y after this code is executed?

val y = (math floor 3.1415 * 2)

short
double
int
bigInt

Q17. When using pattern matching, which character matches on any object?

%
_
^
-

Reference: Pattern Matching

Q18. You have created an array using val. Can you change the value of any element of the array—and why or why not?

Yes, the reference to the array is immutable, so the location that the array points to is immutable. The values in the array are mutable.
The 0th element is immutable and cannot be modified. All other elements can be modified.
Yes, val does not make arrays immutable.
No, val makes the array and values of the array immutable.

Explanation:

val a1 = Array(1, 2, 3)
a1{1} = 3 // OK
a1 = Array(1, 3, 3) // error: reassignment to val

Q19. What is the output of this function?

def main () {
     var a = 0
     for (a<-1 until 5){println(a)}

1,2,3,4,5
0,1,2,3,4
1,2,3,4
2,3,4,5

Q20. What do you call objects with immutable state?

singletons
stationary objects
functional objects
fixed objects

Note: singletons may have mutable state

Q21. You have written a Scala script. How would you access command-line arguments in the script?

use array named args
use tuple named args
use numbered variables with a _ prefix for example _ 1, _ 2, _ 3
use numbered variables with a $ prefix - for example $1, $2, $3

Q22. What does this code return? `val x = 3; if (x > 2) x = 4 else x = x*2`

4
an error
6
3

Q23. Which statement returns a success or a failure indicator when you execute this code?

val MyFuture = Future {runBackgroundFunction() }

myFuture.onComplete
myFuture(status)
myFuture.Finished
complete(myFuture)

Q24. To denote a parameter that may be repeated, what should you place after type?

%
&
_
-

Q25. What is called when a superclass has more than one subclass in Scala?

polyinheritance
multilevel inheritance
multimode inheritance
hierarchical inheritance

Q26. One way to improve code reliability is to use `__` , which will evaluate a condition and return an error if the condition is violated.

packages
polymorphisms
assertions
traits

Q27. Which statement about if-else-if-else statements is true?

If the first else-if does not succeed, then no other else-ifs are tested.
If an else-if does not succeed, then none of the remaining else-if statements or elses will be tested.
All else-if statements are tested in all cases.
If an else-if succeeds, then none of the remaining else-if statements or elses will tested.

Q28. What do you call the process of changing the definition of an inherited method?

recursive methods
currying methods
redefining methods
overriding methods

Q29. To denote a parameter that may be repeated, what should you place after the type?

_
*
%
&

Reference: Repeated Parameters in Scala

Q30. What is the code below equivalent to?

myClass.foreach(println _)

myClass.foreach(println ())
myClass.foreach(print NIL)
myClass.loop(println ())
myClass.foreach(x => println(x))

Q31. What is an advantage of an immutable object?

Immutable objects use less memory than their mutable counterparts.
Immutable objects do not require error handling.
Immutable objects can be used in classes, mutable objects cannot.
Immutable objects are threadsafe.

Q32. You want to create an iteration loop that tests the condition at the end of the loop body. Which iteration would you use?

do-while loop
while loop
for loop
do-until loop

Q33. What can you use to make querying a database more efficient, by avoiding the need to parse the SQL string every time a query is executed from Scala?

database driver
connection
prepared statement
SQL view

Reference: PreparedStatement from Java which is also used in Scala

Q34. Which is not a member of the collections hierarchy?

Set
Seq
Hash
Map

Q35. Which term makes the contents of packages available without prefixing?

use
include
import
assertion

Q36. If you wanted to find the remainder after division, what operator would you use?

%
DIV
//
/

Q37. What are defined inside a class definition?

method
fields and methods
fields, methods, and packages
fields

Q38. What defines methods and fields that can then be reused by mixing into classes?

singleton
assertion
trait
monad

Q39. When do you need to explicitly state the return type in a function definition?

when the function has no side effects
when the function returns a Unit type
when the function is recursive
when the function has side effects

Q40. Why would you make a field private?

so only methods in the same file can access the field
so only methods in the same package can access the field
so only methods in the same class could access the field
so only methods defined in a Java class can access the field

Q41. What's the difference between `.equals` and `==`?

They do the exact same thing
== won't work on objects
== cannot be applied to String
== is a wrapper of .equals() and checks for nulls

Source:

Q42. What is denotes the intersection between two sets?

||
&&
&
%