Kotlin

Unlike Java or C#, Kotlin doesn’t have static members or member functions. Kotlin recommends to simply use package-level functions instead.

What if I say there is a class called Nothing in Koltin.

And What does it do? Nothing.

The time I read about the class Nothing for the first time, it sounds interesting to me. This class has no instance and it is used to represent a value which never exists. This class is also used to represent a return type from a method that will never return.

Any expression in Kotlin may be marked with a label. This can be used to as an identifier. A label can be defined in Kotlin using label name followed by @ sign in front of any expression.

I started developing Android apps in Java where encapsulation of object-oriented programming was achieved through declaring variables as private fields with their getter and setter as public methods. The moment I converted my Java code to Kotlin, it replaced each variable along with its getter and setter with just a single line of code. Although I was amazed at how can a single line of code replace the complete variable with the same functionality, but later on understanding it, I started liking writing the code in Kotlin. Let’s understand how it works in Kotlin.

While converting all my java code to kotlin, one of the strange syntax change I observed was the for loop in both the languages. Later I realized in Kotlin, there are few concepts which are completely different from java or any other another language for loops.

when operator is a replacement of switch operator in other languages.

when operator matches its argument with all the branches until it matches with anyone, else it executes the else block.

‘in’ operator in Koltin is used to check the existence of particular variable or property in a Range or Collection whereas a ‘!in’ operator is just a not of ‘in’ operator and returns true if the condition is false. It can also be used to iterate over a range or collection.

Type check is a way of checking the type(DataType) or Class of a particular instance or variable while runtime to separate the flow for different objects. In few languages, it’s also denoted as Run Time Type Identification (RTTI).

In Kotlin, the type system distinguishes between references that can hold null (nullable references) and those that can not (non-null references). For example, a normal property can’t hold a null value and will show a compile error.

There can be two ways to declare and initialize a var property

var variable : CustomClass = CustomClass() 
 or
var variable : CustomClass? = null

The first property is initialized while declaration itself and doesn’t require a null check (?.) while using it.

What is a higher-order function?

In Kotlin, a function can be passed as a parameter or can be returned from a function, the function which does the same is known as a higher-order function. In other words, a higher-order function is a function that takes functions as parameters or returns a function.

What is Backing Field ?

Backing field is an autogenerated field for any property which can only be used inside the accessors(getter or setter) and will be present only if it uses the default implementation of at least one of the accessors, or if a custom accessor references it through the field identifier. This backing field is used to avoid the recursive call of an accessor which ultimately prevents the StackOverflowError.