# 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. - [x] copy() allows you to change values during the copying process; clone() does not. # What value does this code return? ```scala val m1 = Map("a"->1,"b"->2,"c"->3) m1("a") ``` - [ ] a - [ ] 2 - [ ] b - [x] 1 # What is one way to avoid low-level parallelization details? - [ ] monads - [ ] literal functions - [ ] partially applied functions - [x] parallel collections # What do you use in ScalaTest to see a detailed diagram of error messages when a test fails? - [ ] ArgumentExceptions - [ ] AssertionException - [x] DiagrammedAssertions - [ ] JUnit # What data type would you use to store an immutable collection of objects that contain a fixed number of varying types? - [ ] Array - [ ] ImmutableCollection - [ ] List - [x] Tuple # 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. - [x] The function returns no value. - [ ] Returning unit types to the function is a closures. # What type of number is 1234.e5? - [ ] hexadecimal - [ ] short - [x] floating point - [ ] long # 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)]` - [x] `List` # What type of object does this code create? ``` val x = (1234, "Active") ``` - [ ] List - [ ] Map - [x] Tuple - [ ] Array # Which is a subclass of all classes? - [ ] AnyVal - [ ] AnyRef - [ ] Method - [x] Null [Null in Scala Standard library](https://www.scala-lang.org/api/current/scala/Null.html). The question is a bit incorrect - Null is a subtype of every type _except those of value classes_ # 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. - [x] 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 ```scala val a = Array(1, 2, 3, 4, 5) for { e <- a if e > 2 } yield e ``` # 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](https://docs.scala-lang.org/tour/pattern-matching.html) is meant here. # What is the value of z after executing this code? ``` val y = List('a','b') val z = y::List('c') ``` - [ ] List(a,b,c) - [x] List(List(a, b), c) - [ ] List(c,a,b) - [ ] List(c,List(a,b)) # What term is used to specify a precondition? - [x] assert - [ ] require - [ ] precondition - [ ] mustHave # 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` - [x] `scala.util.Try` [scala.util.Try](https://www.scala-lang.org/api/current/scala/util/Try.html) # What is the data type of y after this code is executed? ``` val y = (math floor 3.1415 * 2) ``` - [ ] short - [x] double - [ ] int - [ ] bigInt # When using pattern matching, which character matches on any object? - [ ] `%` - [x] `_` - [ ] `^` - [ ] `-` [Pattern Matching](https://docs.scala-lang.org/tour/pattern-matching.html) # You have created an array using val. Can you change the value of any element of the array—and why or why not? - [x] 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**: ```scala val a1 = Array(1, 2, 3) a1{1} = 3 // OK a1 = Array(1, 3, 3) // error: reassignment to val ``` # What is the output of this function? ```scala def main () { var a = 0 for (a<-1 until 5){println(a)} ``` - [ ] 1,2,3,4,5 - [ ] 0,1,2,3,4 - [x] 1,2,3,4 - [ ] 2,3,4,5 # What do you call objects with immutable state? - [ ] singletons - [ ] stationary objects - [x] functional objects - [ ] fixed objects **Note:** singletons may have mutable state # You have written a Scala script. How would you access command-line arguments in the script? - [x] 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 # What does this code return? `val x = 3; if (x > 2) x = 4 else x = x*2` - [ ] 4 - [x] an error - [ ] 6 - [ ] 3 # Which statement returns a success or a failure indicator when you execute this code? `val MyFuture = Future {runBackgroundFunction() }` - [x] myFuture.onComplete - [ ] myFuture(status) - [ ] myFuture.Finished - [ ] complete(myFuture) # To denote a parameter that may be repeated, what should you place after type? - [ ] `%` - [ ] `&` - [ ] `_` - [x] `-` # What is called when a superclass has more than one subclass in Scala? - [ ] polyinheritance - [ ] multilevel inheritance - [ ] multimode inheritance - [x] hierarchical inheritance # 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 - [x] assertions - [ ] traits # 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. - [x] If an else-if succeeds, then none of the remaining else-if statements or elses will tested. # What do you call the process of changing the definition of an inherited method? - [ ] recursive methods - [ ] currying methods - [ ] redefining methods - [x] overriding methods # To denote a parameter that may be repeated, what should you place after the type? - [ ] `_` - [x] `*` - [ ] `%` - [ ] `&` [Repeated Parameters in Scala](https://www.baeldung.com/scala/repeated-parameters) # What is the code below equivalent to? ```scala myClass.foreach(println _) ``` - [ ] `myClass.foreach(println ())` - [ ] `myClass.foreach(print NIL)` - [ ] `myClass.loop(println ())` - [x] `myClass.foreach(x => println(x))` # 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. - [x] Immutable objects are threadsafe. # You want to create an iteration loop that tests the condition at the end of the loop body. Which iteration would you use? - [x] do-while loop - [ ] while loop - [ ] for loop - [ ] do-until loop # 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 - [x] prepared statement - [ ] SQL view [PreparedStatement from Java](https://docs.oracle.com/javase/8/docs/api/java/sql/PreparedStatement.html) which is also used in Scala # Which is _not_ a member of the collections hierarchy? - [ ] Set - [ ] Seq - [x] Hash - [ ] Map # Which term makes the contents of packages available without prefixing? - [ ] use - [ ] include - [x] import - [ ] assertion # If you wanted to find the remainder after division, what operator would you use? - [x] % - [ ] DIV - [ ] // - [ ] / # What are defined inside a class definition? - [ ] method - [x] fields and methods - [ ] fields, methods, and packages - [ ] fields # What defines methods and fields that can then be reused by mixing into classes? - [ ] singleton - [ ] assertion - [x] trait - [ ] monad # 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 - [x] when the function is recursive - [ ] when the function has side effects # 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 - [x] so only methods in the same class could access the field - [ ] so only methods defined in a Java class can access the field # What's the difference between `.equals` and `==`? - [ ] They do the exact same thing - [ ] `==` won't work on objects - [ ] `==` cannot be applied to `String` - [x] `==` is a wrapper of `.equals()` and checks for nulls [Source:](https://www.programmersought.com/article/3717957705/) # What is denotes the intersection between two sets? - [ ] || - [ ] && - [x] & - [ ] % [Source:](https://docs.scala-lang.org/overviews/collections/sets.html) # What do you call a function defined in a block? - [ ] private function - [ ] block function - [ ] local function - [ ] method # What do you call a Scala method that is parametrized by type as well as by value? - [ ] multimode method - [ ] polymorphic method - [ ] closure - [ ] collection method # What type of exception is thrown when a precondition is violated? - [x] IllegalArgumentException - [ ] NumberFormatException - [ ] NullPointerExcepetion - [ ] MalformedParameterException # In scala what is precondition? - [ ] a constraint on where a method may be called from - [ ] a constraint on values passed to a methode constructor - [x] a class of predifined error messages - [ ] a class of Boolean operators # What would you change in this code to make it execute in parallel? ``` val myNums = (1 to 500).toList list.map(_ + 1) ``` - [x] Change **list.map** to **list.par.map.** - [ ] Change **toList** to **toListPar** - [ ] Change **val** to **val.par** - [ ] Change **toList** to **toParallelList** # What is a free variable? - [x] a variable defined outside a function - [ ] a variable referenced in a function that is not assigned a value by that function - [ ] a variable that has a global scope - [ ] a variable defined in a class and available to all methods in that class # What's the best way to execute code in the background in a separate thread? - [ ] AltThread - [ ] AltFuture - [ ] AltProcess - [x] Future # What value does this code return? ```scala x= List(1,2,4); x(1)? ``` - [ ] (1,2,4) - [ ] 1 - [ ] Nil - [x] 2