Scala interview questions

Scala is a general-purpose high-level programming language that combines object-oriented and functional programming in one concise. Scala was designed by Martin Odersky and supports Inferred, static, strong, structural typing discipline.

• Mutable
• Immutable

By default, immutable map is supported by scala. To use the mutable map, the programmer needs to import the “scala.collection.mutable”. It is an explicit class. “mutable.map” is the syntax for using the mutable and immutable class in the same program. To access the immutable class, we just have to use the name of the map and it can be accessed.

• As the name suggests, it is a scalable programming language. It is highly scalable. Its high maintainability, productivity, and testability features make it more usable which turns out to be an advantage and hence it is preferred more.
• Scala consists of singleton and companion objects. These objects in scala, unlike the JVM languages provide a clearer solution to every problem.
• The need of ternary operator gets eliminated in scala as “if blocks”, “for-yield loops”, and “code” in braces return a value.

Instead of having static methods or variables, scala has singleton or companion objects. These objects are then compiled to classes which have static methods. Some advantages of these companion objects are listed below:

• These are beneficial as they can be used for encapsulating things. They also act as a bridge and hence functional and object-oriented programs can be written easily.
• These companion objects also help in keeping the scala programming code more concise because the static keyword need not be added to each and every attribute.
• A clear separation between the static and non-static methods is maintained with the help of these companion objects.

• Nil- it is used to initialize an empty list since it is an object which extends list.
• Null- null in scala is used to provide compatibility with the java null keyword or to provide a type for the null keyword. It also represents the absence of type information for complex types.
• None- the “none” pattern in scala is used to remove null values from the scala code.
• Nothing- it is used for providing the return type for the operations that can affect the normal flow of program.

• Apply method- this method is used to assemble an object from its components. For eg.- if an employee object needs to be created, then the two components namely- first name and last name should be used and should be composed using the apply method.
• Unapply method- when we want to decompose the objects from its components, then we make use of this unapply method. Reverse process is followed while making use of the unapply method. So, the employee object can be decomposed into two components namely- first name and last name.

• An array is a sequential mutable data structure. Whereas, a list is an immutable recursive data structure.
• In scala, an array is an invariant. Whereas, a list is a covariant data structure.
• The size of an array is fixed and cannot be changed easily. Whereas, the size of a list may increase or decrease based on the operations performed by it.

Implicit parameters in Scala are used when we want to invoke a function without passing all the parameters. The default values of all the parameters or the parameters which we want to use are set as implicit. When implicit parameters are not used the local value of that parameter is used. An implicit keyword needs to be used if you want to make value, function parameter, or a variable as an implicit parameter. Once the value becomes implicit, we need not pass all the parameters to invoke a particular function.

Predef in Scala is used for providing type aliases for the commonly know scala types such as collection types Map, Set, and the List constructors.

Unit is a type in Scala that is used as a return statement for a function when no value is to be returned. It is a subtype of scala.AnyVal.

Akka in Scala is a toolkit and runtime for building highly concurrent, distributed, and fault-tolerant applications on the JVM and is written in Scala, with language bindings provided for both Scala and Java. Akka’s approach to handling concurrency is based on the Actor Model. In an actor-based system, everything is an actor, in much the same way that everything is an object in object-oriented design. A key difference, though – particularly relevant to our discussion – is that the Actor Model was specifically designed and architected to serve as a concurrent model whereas the object-oriented model is not or in other words, in a Scala actor system, actors interact and share information, without any presupposition of sequentiality. The mechanism by which actors share information, and task one another, is message passing.