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Scala Interview Question

  1. Scala is a scripting language & object functional programming designed to express solutions for general software applications.
  2. Scala refers to a Java-based Hybrid language that combines the features of object-oriented & functional-oriented programming language. It can compile the written code & integrate it with the Java Virtual Machine (VM).
  3. Scala means a general-purpose programming language that supports imperative, object-oriented, functional, & programming approaches. Everything in Scala is an object, whether it is a number or a function. Scala was designed in 2004 by Martin Odersky.
  1. Scala set represents a collection of pairwise variant elements of the same type. It does not have any duplicate elements. There are two types of Scala sets, mutable set, and immutable set. All the operations on a Scala set can be expressed in the following methods: All the operations on a Scala set can be expressed in the following methods:
    • Head: It returns the Scala set’s first element.
    • tail: It returns a Scala set containing all the elements except the first.
    • isEmpty: It returns true if the Scala set is empty, otherwise false.
  2. A Scala set is a collection of unique elements with no duplicates. It is classified into two types: mutable and immutable sets. However, Scala uses immutable sets by default. Below are a few methods for set operations:
    • head: It returns the first element or of the set.
    • tail: It returns the entire set except for the head or first element.
    • isEmpty: It checks whether the set is empty & then returns the Boolean.
  1. A Scala map is a collection of value or key pairs. Any value can be retrieved based on the Scala map’s key. In a map, there are no unique values, but the keys are always unique.
  2. A Map in Scala means a collection of value & key pairs that helps in retrieving the value based on a key. It is an effective collection of variables that include both keys and values. The values are not unique in a Scala map, unlike keys that are unique.
  3. Scala map is a collection of value-key pairs, wherein the key is used to retrieve a value. The keys are unique in a Scala map, but values aren’t unique. Scala has two types of maps; mutable & immutable. However, Scala supports immutable maps by default. To avail the mutable map, programmers need to import the class scala.collection.mutable.Map explicitly. When programmers want to use both immutable & mutable maps in the same program, then a mutable map can be accessed at & the immutable map can be simply accessed with the map’s name.
    1. Scala is a less error-prone functional style;
    2. It supports high productivity & maintainability;
    3. Scala is highly scalable;
    4. It provides higher testability;
    5. Scala also offers concurrent programming features.
  1. There are various advantages of Scala, as follows.
    1. Maintainable
    2. Scalable
    3. Concise code
    4. Productive
    5. Concurrent programming
    6. Native Tuples & Testable codes
    7. No Boilerplate codes
    8. Singleton objects are a clearer solution than the static
  2. Some major advantages of Scala are:
    1. Highly Scalable and Testable
    2. Highly Productive & Maintainable
    3. It enables Concurrent Programming
    4. It is both Functional and Object-Oriented
    5. Scala has no Boilerplate Codes
    6. Singleton objects are a cleaner solution than the Static
    7. Scala Arrays use the regular Generics
    8. Scala has Concise Codes & Native Tuples
    1. Scala has immutable “val” as the first-class language feature. Scala’s “val” is similar to the Java final variable. Contents may mutate, but the top reference is immutable.
    2. Scala lets ‘for-yield loops’, ‘if blocks,’ & ‘code’ in braces to return the value. It is most preferable & eliminates the need for a separate ternary operator.
    3. Scala has singleton objects which is a clear solution than C#/C++/Java’s classic static.
    4. Arrays use regular generics in Scala, while generics get bolted on as the afterthought and completely separate but have overlapping behaviors with arrays in the other languages.
    5. Persistent immutable collections are default & built into the standard library.
    6. Scala has a concise code & native tuple.
    7. Scala doesn’t have any boilerplate code.
    1. Scala is not only object-oriented, but it also has functional programming language features.
    2. Scala is readable, concise, error-free, easy to code & compile.
    3. Scala deploys concurrency; thus, it is easy to make synchronization.
    4. Third-party libraries in Scala can be easily added in the form of language constructs.
    5. It works in a multicore architecture environment.
  1.  A class defines a type in terms of composition & methods of other types. It is an object’s blueprint. In contrast, an object is a singleton, a class’s unique instance. An anonymous class is created for each object; it inherits from whatever classes you have declared object to implement.
  2. A class refers to a blueprint or a definition. In terms of compositions & methods of other types, a class defines a type. However, an object is a singleton & a unique instance of a class. Each object in the code has an anonymous class for it.
  1. ‘Recursion’ implies a function that calls itself. It is a technique often used in functional programming. For a tail-recursive, the call back to a function should be the last function to be performed.
  2. Recursion refers to a function in Scala that calls itself. When function A calls function B, that further calls function C, it is known as recursion. This technique is mostly used in functional programming.
  1. Trait in Scala is used to define the object types specified by a signature of the supported methods. It can be partially implemented, but traits may not have constructor parameters. A Scala trait consists of field definition & method that can be reused by mixing them into classes.
  2.  A Scala trait is a partially implemented interface that can hold non-abstract and abstract methods.
  3. A trait in Scala is a special type of class that allows the use of multiple inheritances. Though a trait can only extend one class, a class can have multiple traits. Unlike classes, Scala traits cannot be instantiated.
  4. A trait is similar to an interface with partial implementation. Scala trait is a collection of both non-abstract and abstract methods. You can create a trait containing all the abstract methods or a few abstract and non-abstract methods.
  1. There are no specific rules for when you can use traits in Scala, but there is a set of guidelines that you can consider:
    • Make it a concrete class if the behavior will not be reused. It is not a reusable behavior.
    • To inherit from a trait in a Java code, use an abstract class.
    • If efficiency is essential, use a class.
    • Make it a Scala trait if it might be reused in unrelated & multiple classes. In different parts of a class hierarchy, only Scala traits can be mixed into different parts.
    • You can utilize an abstract class if you want to distribute it in a compiled form & expect outside groups to write classes inheriting from it.
  2. Scala trait is mostly used when we need dependency injection. In Scala, there are no special packages or annotations to be imported. We need to initialize a class with the trait & done, dependency is injected.
  1. Case classes offer a recursive decomposition mechanism through pattern matching. The case classes are just like regular classes that export their constructor parameter. The constructor parameters of the case classes are directly accessible & are treated as public values.
  2. Case classes refer to the standard classes declared with a special modifier. Such classes provide a recursive decomposition mechanism through pattern matching. The case classes export their constructor parameters accessed directly & treated as public values. For a case class, companion objects & their associated methods get automatically generated. All the methods in a class and methods in a companion object are generated based on the parameter list. A major advantage of a case class is that it automatically generates the methods from a parameter list.
  3. Scala case classes are regular classes, immutable by default & decomposable via pattern matching. It uses equal methods to structurally compare instances. It does not use the new keyword to instantiate an object.
  1. Tuples in Scala combine a fixed number of items so that they can be passed around as a whole. It is immutable and can hold objects with different types, unlike a list or an array.
  2. Tuples in Scala combine a finite number of items together so a programmer can pass the tuple around as a whole. Unlike a list or an array or list, a tuple is immutable & can hold the objects with different data types.
  1. Function Currying refers to transforming the function that takes multiple arguments into a function that takes a single argument. Scala supports various similar techniques as language, such as Haskell and LISP. However, function currying is the most misunderstood & least used technique.
  2. We can transform a function that takes multiple arguments into the functions that take only a single argument through the function currying technique. It comes in handy working with a higher-order function.
  3. Currying is a simple technique that transforms a function that takes multiple arguments into a function that takes a single argument.
  1. Implicit parameter is a way to find a method’s parameters. It is similar to default parameters but has a different mechanism for finding a “default” value. The implicit parameter refers to a parameter to a constructor or method marked as implicit. It means that if a parameter value is not mentioned, then the compiler will search for the “implicit” value defined within the scope.
  2. We use implicit parameters when we need a function that could be invoked without passing all the parameters. We provide the default values for all the parameters or parameters we want to be used as implicit. When a function is invoked without passing an implicit parameter, the local value of that parameter is used. We need to utilize implicit keywords to make a function parameter, value, or variable implicit.
  3. An implicit parameter enables you to invoke a function without passing the parameters. For that, you need to provide a default value for all the parameters that you want to declare as implicit. To make a variable, value, or function parameter ‘implicit,’ you require an implicit keyword.
  1. A closure refers to a function whose return value depends on the variable’s value declared outside a function.
  2.  The closure is a function in Scala whose return value is dependent on either one or more variables’ value declared outside the function.
  1.  A Monad is that object which wraps another object. You can pass the Monad mini-program or function to perform data manipulation of the underlying object instead of directly manipulating an object. Monad chooses how to apply a program to an underlying object.
  2. Monad in Scala is an object that helps in wrapping another object according to the mini-program, a function to perform data manipulation on an underlying object. It manipulates an object indirectly and chooses the method to apply for a program on the underlying object.
  3. A Monad in Scala can pass functions to manipulate an underlying object’s data. It eliminates the need to manipulate an object directly. It is an object that wraps another.
  1.  An anonymous function in a source code is known as ‘function literals.’ During run time, function literals get instantiated into the objects called function values. Scala provides an easy syntax to define an anonymous function.
  2. Scala anonymous function in the source code is also called function literals. The function literals are instantiated into the objects (function values) during run time, which provides an easy Syntax for defining the anonymous functions.
  1. Higher-order functions in Scala are those functions that take other functions as parameters/arguments or returns functions as their result.
  2. Higher-order functions refers to the function that does one or more functions as arguments or returns a function as its outcome.
  3. A Higher-order function that function which does at one of the following:
    1. Takes one or mutiple functions as arguments, or;
    2. Returns function as its result
  1. You can define a variable either by using a val keyword or a var keyword in Scala. The difference between var & val is that the former is much like a Java declaration, but the latter is slightly different.  One cannot change a reference point to another reference once the variable is declared with a val keyword. In contrast, a variable defined using a var keyword is mutable & can be changed multiple times.
  2. Both value & var keywords are used for declaring variables. However, var denotes a variable whose value is mutable & can be updated later in the code. On the other hand, val is like the final or constant value that cannot be changed.
  3. In Scala, both val & var keywords are used to define variables. However, they share some significant differences as follows:
    1. Var stands for a variable & val stands for value.
    2. Variables can be changed, but values cannot be changed.
    3. Var is used to define a mutable variable.
    4. Val is used to defining an immutable variable.
    5. Var is a ‘variable,’ but val is the final variable.
  1. An ‘option’ in Scala is a generic type that can be ‘some’ generic value or none. ‘Queue’ often uses an option to represent primitives that may be null.
  2. Scala option is a container for one or zero elements of a given type. An option can be some or none object that represents a missing value.
  1. To append into a list in Scala, use the “:+” single value.
  2. To append data in the list, you must use “:+,” which appends a single value into the list.

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