computer science

Kotlin

Kotlin is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Kotlin rather than just read about it. In short: Kotlin () is a cross-platform, statically typed, general-purpose high-level programming language with type inference. Kotlin is designed to interoperate fully with Java, and the Java virtual machine (JVM) version of Kotlin's standard library depends on the Java Class Library.

Key takeaways

Kotlin belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Kotlin to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Kotlin from memory before moving on to harder problems.

Reference excerpt

Kotlin () is a cross-platform, statically typed, general-purpose high-level programming language with type inference. Kotlin is designed to interoperate fully with Java, and the Java virtual machine (JVM) version of Kotlin's standard library depends on the Java Class Library. Type inference allows for more concise syntax than Java, while null-safety features reduce a common class of runtime errors. Kotlin mainly targets the JVM, but also compiles to JavaScript (e.g., for frontend web applications using React) or native code via LLVM (e.g., for native iOS apps sharing business logic with Android apps). JetBrains bears language development costs, while the Kotlin Foundation protects the Kotlin trademark. On 7 May 2019, Google announced Kotlin had become its preferred language for Android app developers. As of 2024, over 95% of the top 1,000 Android apps on Google Play contain Kotlin code. In May 2024, JetBrains released Kotlin 2.0 featuring the new K2 compiler—a complete rewrite offering up to twice the compilation speed of its predecessor—as well as stabilised support for Kotlin Multiplatform. That same month, Google formally endorsed Kotlin Multiplatform at Google I/O 2024, recommending it as the approach for sharing business logic across Android, iOS, and other platforms.

History

Name The name is derived from Kotlin Island, a Russian island in the Gulf of Finland, near Saint Petersburg. Andrey Breslav, Kotlin's former lead designer, mentioned that the team decided to name it after an island, in imitation of the Java programming language, which shares a name with the Indonesian island of Java.

Development The first commit to the Kotlin Git repository was on 8 November 2010. In July 2011, JetBrains unveiled Project Kotlin, a new JVM language that had been under development for a year. JetBrains lead Dmitry Jemerov said that most languages lacked the features they were looking for, except for Scala. However, he cited Scala's slow compilation time as a deficiency. One of Kotlin's stated goals is to compile as quickly as Java. In February 2012, JetBrains open-sourced the project under the Apache 2 license. Kotlin 1.0 was released on 15 February 2016, which is considered the first officially stable release, and JetBrains has committed to long-term backwards compatibility starting with this version. At Google I/O 2017, Google announced first-class support for Kotlin on Android. On 7 May 2019, Google announced that Kotlin is now its preferred language for Android app developers. In November 2023, Kotlin/Native was declared stable with version 1.9.20, enabling production-ready compilation to native binaries for iOS, macOS, Linux, and Windows without a JVM. Kotlin Multiplatform (KMP), which allows sharing business logic across Android, iOS, server, and desktop from a single codebase, also reached stable status in November 2023. In May 2024, JetBrains released Kotlin 2.0 at KotlinConf 2024 as the most significant release in the language's history. The centrepiece was the stable K2 compiler—a complete rewrite of the original compiler frontend from scratch—which unifies all target platforms (JVM, JavaScript, WebAssembly, and Native) into a single pipeline. The K2 compiler was validated against 10 million lines of code across 80,000 projects by more than 18,000 developers before release. Benchmarks showed compilation speed improvements of up to 94% in some projects, with the analysis phase up to 376% faster than the previous compiler. Also in May 2024, Google officially endorsed Kotlin Multiplatform at Google I/O 2024, announcing first-class tooling and library support for KMP on Android, and revealing that Google Workspace uses KMP for the shared business logic of Google Docs across Android, iOS, and web.

Design Development lead Andrey Breslav has said that Kotlin is designed to be an industrial-strength object-oriented language, a "better language" than Java, and still fully interoperable with Java code, allowing companies to make a gradual migration from Java to Kotlin. Semicolons are optional as a statement terminator; in most cases, a newline is sufficient for the compiler to deduce that the statement has ended. Kotlin variable declarations and parameter lists place the data type after the variable name (separated by a colon), similar to Ada, BASIC, Pascal, TypeScript, and Rust. This, according to an article from Roman Elizarov, current project lead, results in alignment of variable names and is more pleasing to the eyes, especially when there are a few variable declarations in succession, and one or more of the types are too complex for type inference, or need to be declared explicitly for human readers to understand. The influence of Scala in Kotlin can be seen in the extensive support for both object-oriented and functional programming and in several specific features:

There is a distinction between mutable and immutable variables (var vs val keyword) All classes are public and final (non-inheritable) by default Functions and methods support default arguments, variable-length argument lists, and named arguments Kotlin 1.3 added support for contracts, which are stable for the standard library declarations, but still experimental for user-defined declarations. Contracts are inspired by the design-by-contract programming paradigm. Like Scala.js, Kotlin code can be transpiled to JavaScript, enabling interoperability between Kotlin and JavaScript and allowing either writing complete web applications in Kotlin or sharing code between a Kotlin backend and a JavaScript frontend.

Syntax

Procedural programming style Kotlin relaxes the Java restriction on static methods and variables, allowing them to exist outside a class body. Static objects and functions can be defined at the top level of the package without requiring a redundant class-level scope. For compatibility with Java, Kotlin provides the JvmName annotation, which specifies the class name used when the package is viewed from a Java project. For example, @file:JvmName("JavaClassName").

Main entry point

As in C, C++, C#, Java, and Go, the entry point to a Kotlin program is a function named main, which may be passed an array containing any command-line arguments. This is optional since Kotlin 1.3. Perl, PHP, and Unix shell–style string interpolation is supported. Type inference is also supported.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Kotlin

Start with the simplest possible case. Write down what Kotlin claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Kotlin before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Kotlin ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Kotlin

In research: Kotlin appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Kotlin in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Kotlin is common in secondary-school and first-year university syllabi. It links to neighbouring topics 2011 software, Extensible syntax programming languages, Free software projects, so understanding it makes those chapters shorter.
In everyday life: Look for Kotlin outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Kotlin in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Kotlin means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Kotlin out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Kotlin in simple terms?

Why does Kotlin matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Kotlin?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Kotlin.