Kotlin Tutorial for Beginners

Introduction to Kotin

Kotlin is a general-purpose programming language. It is a statically typed language with type inference and a cross-platform language.

(Type inference: The automatic detection of the data type of a value or an expression in a programming language.)

What is Kotlin?

Kotlin is a ‘Pragmatic’ language for JVM. It becomes one of the most popular languages. It combines object-oriented and functional programming features into it.

Reasons for Kotlin development

Kotlinwas developed for multi-platform and modern applications. Kotlin runs on JVM, i.e. Java Virtual Machine and compiles into JVM bytecode.

Kotlin developed at JetBrains.JetBrains and Google sponsored the Kotlin, through the Kotlin Foundation.

‘.kt’ and ‘.kts’ are the file extensions in Kotlin.

History of Kotlin

The developers at JetBrains were getting difficulty while developing the IDE. Most languages do not have features as per their necessity. Scala is an exception with a deficiency of slow compilation time. They decided to develop a new language having features like ‘Scala’ and faster compilation time like ‘Java.’ Andrey Breslavis one of the main lead from the development team.

In 2010, they started working on a new project. The name for the new project came from the ‘Kotlin Island,’ which is Russian Island.

In July 2011, JetBrains announced publically first-time ‘project Kotlin’ as a new language for JVM.

In February 2012, JetBrains open-sourced the Kotlin under Apache 2 license.

Google officially declared Kotlin support to Android for mobile development in 2017.

The latest stable release/ version of Kotlin 1.3.21 released on 6 February 2019.

Facts to remember about ‘Design Pattern of Kotlin’

Andrey Breslav said that Kotlin designed to be an ‘industrial strength’ object-oriented language.

In most cases, a newline is sufficient to understand the compiler that the statement has ended. In Kotlin, semicolon (statement terminator) is optional.

The data type of Kotlin variable comes after the variable name at the time of variable declaration. [Variable_name data-type]

The data type of parameters also comes after the parameter name.

Mutable variable in Kotlin declared with the keyword ‘val,’ whereas the Immutable variable declared with ‘var’ keyword.

All Class members are ‘Public’ by default.

All Classes are ‘Final’ by default. Hence, to achieve the inheritance property, the Base class should be declared open using ‘open’ keyword.

Features of Kotlin

  1. Open-Source
  2. Interoperable with Java and Android
  3. Concise and Expressive
  4. Easy to Learn
  5. Tool friendly
  6. Safe
  7. Versatile
  8. Functional Programming
  9. Data Classes
  10. Collection Filtering
  11. Extension Functions
  12. Lazy-Loading

Let us understand the Kotlin features in detail:


Kotlin distributed under the Apache License 2.0. The Compiler, i.e. Kotlin + Compiler, enhancements to basic java libraries and build tools, IntelliJ Idea plugin all are open source.

Interoperable with Java and Android

Koli language is 100% interoperable with java and android. Therefore, all the java code or Android code works smoothly with Kotlin. Besides, it allows Kotlin projects to compile in a JavaScript module.

Concise and Expressive

The meaning of concise is ‘giving a lot of information clearly in a few words.’ Kotlin reduces the number of lines of codes as compared to java. Result to this, Kotlin becomes expressive, i.e. easy to write code.

Easy to Learn

Kotlin influenced by Java, Scala, C#, Groovy, Gosu, and JavaScript. If you are familiar with any one of the languages mentioned here, then Kotlin became one of the easiest languages to learn. If you are not familiar with (Java, Scala, C#, Groovy, Gosu, and JavaScript)then also, Kotlin is easy to learn because it is concise and expressive.


Kotlin is a tool-friendly language. Kotlin runs on any Java IDE.


Kotlin removes the danger of null references from the code. Kotlin interoperates with the loosely typed environment such as JavaScript ecosystem. It is a statically typed language. Type checking is done at compile time hence minor bugs caught at an early stage.


Kotlin builds Android applications, server-side applications and front-end code for browsers. Kotlin can adapt to different environments. Hence, it is versatile in nature.

Functional Programming

Kotlin is functional programming. Kotlin achieves functional programming through lazy evaluations, lambda expressions, operator overloading, and many useful methods to work with Collections.

Data classes

The necessity of class is always a hot subject for programming language designer. In Java, to know the real use of class needs to skip some lines whereas in Kotlin, the same code can be written in simple and minimum lines of code. Therefore, ‘data classes’ is one of the best features in the Kotlin.

Collection Filtering

It is necessary for developers when they are working with API; they have to deal with Collections. It becomes easy to tell the result list with the help of Katlin’s collections filter.

Extensions Functions

Extensions of Kotlin are handy because they allow the developer to add functions in a class without modifying the source code. The developer can add methods/ functions to class as per user basis just like Scala’s implicit methods.

Lazy Loading

When Kotlinis used for Android applications, the lazy loading feature increases the startup time that’s why android applications content displays faster. It is very beneficial for an android developer who wants to reduce their applications startup time. With the help of lazy loading, Kotlin developer can load the resources only in main memory.

Tools support for Kotlin

Following tools support for Kotlin:

  1. IntelliJ IDEA
  2. Eclipse
  3. Android Studio
  4. Emacs

IntelliJ IDEA has plug-in support for Kotlin.

JetBrains provides Plugin support to Eclipse for Kotlin.

Android Studio has the official support of Kotlin since Android Studio 3.

Emacs support Kotlin, as Kotlin mode is present in the melpa package repository.

Applications of Kotlin

  • Server-side applications
  • Creating web applications
  • Mobile applications

Possible future projects in Kotlin

  • Cross-platform game development
  • Cross-platform mobile development
  • Data Analysis and Machine Learning
  • Server-side and microservices

Disadvantages of Kotlin

Disadvantages of Kotlin are:

  1. Namespace Declaration

Kotlin supports member functions, local functions as well as top-level functions. The top-level functions present inside the file and outside the class, interface and object. The name top-level comes, as it is not present in any data structure. Hence, they are at the top of the hierarchy of classes and object. These top-level functions help define helper or in utility functions.

There is the possibility of having the same function declarations in many places (member function inside the class, local functions, and top-level functions) in the application. That will create ambiguity which functions called.

2. No Static Declaration

Kotlin does not support static modifier, unlike Java. It will create a problem for conventional java developers.