Kotlin Systems

At kotlin.systems, our mission is to provide a comprehensive resource for developers to learn and master the Kotlin programming language. We strive to offer high-quality tutorials, articles, and tools that enable developers to build robust and efficient applications using Kotlin. Our goal is to create a community of Kotlin enthusiasts who can share their knowledge and experience to help others grow and succeed in their careers. We believe that Kotlin is the future of programming, and we are committed to helping developers stay ahead of the curve by providing the latest insights and best practices. Join us on our journey to explore the power and potential of Kotlin!

Video Introduction Course Tutorial

/r/Kotlin Yearly


Kotlin is a statically typed programming language that runs on the Java Virtual Machine (JVM). It was developed by JetBrains, the company behind the popular IntelliJ IDEA IDE. Kotlin is designed to be concise, expressive, and safe. It is also interoperable with Java, which means that you can use Kotlin code in your existing Java projects and vice versa. In this cheat sheet, we will cover the basics of Kotlin programming, including syntax, data types, control structures, functions, classes, and more.


Kotlin syntax is similar to Java syntax, but with some differences. Here are some of the key syntax elements you should know:

  1. Comments: Kotlin supports both single-line and multi-line comments. Single-line comments start with //, while multi-line comments start with /* and end with */.

  2. Variables: In Kotlin, you declare variables using the var or val keyword. var is used for mutable variables, while val is used for immutable variables.

  3. Data types: Kotlin supports a variety of data types, including Int, Long, Float, Double, Boolean, Char, and String.

  4. Operators: Kotlin supports all the standard arithmetic, comparison, and logical operators, including +, -, *, /, %, ==, !=, <, >, <=, >=, &&, and ||.

  5. Control structures: Kotlin supports if-else statements, when expressions, for loops, while loops, and do-while loops.

  6. Functions: Kotlin functions are declared using the fun keyword. They can take parameters and return values.

Data Types

Kotlin supports a variety of data types, including:

  1. Int: Represents integer values.

  2. Long: Represents long integer values.

  3. Float: Represents floating-point values.

  4. Double: Represents double-precision floating-point values.

  5. Boolean: Represents true/false values.

  6. Char: Represents a single character.

  7. String: Represents a sequence of characters.

Control Structures

Kotlin supports several control structures, including:

  1. If-else statements: Used to execute code based on a condition.

  2. When expressions: Used to execute code based on multiple conditions.

  3. For loops: Used to iterate over a range or a collection.

  4. While loops: Used to execute code while a condition is true.

  5. Do-while loops: Used to execute code at least once, and then continue while a condition is true.


Kotlin functions are declared using the fun keyword. They can take parameters and return values. Here is an example of a simple function:

fun add(a: Int, b: Int): Int { return a + b }

In this example, the function is called add, and it takes two parameters of type Int. It returns the sum of the two parameters.


Kotlin supports object-oriented programming, which means that you can define classes and objects. Here is an example of a simple class:

class Person(val name: String, var age: Int) { fun sayHello() { println("Hello, my name is $name") } }

In this example, the class is called Person, and it has two properties: name and age. The name property is immutable (declared using val), while the age property is mutable (declared using var). The class also has a method called sayHello, which prints a message to the console.


Kotlin supports inheritance, which means that you can create a new class that inherits properties and methods from an existing class. Here is an example of a simple inheritance hierarchy:

open class Animal(val name: String) { open fun makeSound() { println("The $name makes a sound") } }

class Dog(name: String) : Animal(name) { override fun makeSound() { println("The $name barks") } }

In this example, the Animal class is the base class, and the Dog class is the derived class. The Dog class inherits the name property from the Animal class, and it overrides the makeSound method to make a different sound.

Null Safety

Kotlin has a feature called null safety, which helps prevent null pointer exceptions. In Kotlin, you can declare a variable as nullable by using the ? operator. Here is an example:

var name: String? = null

In this example, the name variable is declared as nullable, which means that it can be null. If you try to access a nullable variable without checking for null first, you will get a compile-time error.


Kotlin supports extension functions, which allow you to add new functionality to existing classes without modifying the original class. Here is an example:

fun String.isPalindrome(): Boolean { return this == this.reversed() }

In this example, we define an extension function called isPalindrome for the String class. This function checks whether a string is a palindrome (i.e., reads the same backward as forward).


Kotlin is a powerful and versatile programming language that is gaining popularity among developers. In this cheat sheet, we covered the basics of Kotlin programming, including syntax, data types, control structures, functions, classes, and more. With this knowledge, you should be able to get started with Kotlin and start building your own applications.

Common Terms, Definitions and Jargon

1. Kotlin: A statically typed programming language that runs on the Java Virtual Machine (JVM) and can also be compiled to JavaScript or native code.
2. JVM: Java Virtual Machine, a virtual machine that allows Java bytecode to be executed on different platforms.
3. Bytecode: A low-level representation of Java code that can be executed by the JVM.
4. Native code: Code that is compiled to run directly on a specific platform, such as a computer's processor.
5. IDE: Integrated Development Environment, a software application that provides comprehensive facilities to computer programmers for software development.
6. Syntax: The set of rules that define the structure of a programming language.
7. Variable: A named storage location in memory that holds a value.
8. Data type: A classification of data that specifies the type of value that can be stored in a variable.
9. String: A sequence of characters.
10. Integer: A whole number.
11. Float: A number with a decimal point.
12. Boolean: A data type that can have one of two values: true or false.
13. Array: A collection of elements of the same data type.
14. List: A collection of elements that can be of different data types.
15. Map: A collection of key-value pairs.
16. Function: A block of code that performs a specific task.
17. Parameter: A value that is passed to a function.
18. Return value: The value that a function returns after it has completed its task.
19. Class: A blueprint for creating objects that have similar properties and methods.
20. Object: An instance of a class.

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