Kotlin

Kotlin is a modern, statically typed, general-purpose programming language developed by JetBrains. It is used to build Android applications, server-side software, web applications, cross-platform solutions, and other types of software.

Kotlin is closely integrated with the Java ecosystem: Kotlin code can run on the Java Virtual Machine (JVM) and interact with existing Java libraries and applications. However, the language is not limited to the JVM — Kotlin also supports compilation to JavaScript and native code for various platforms.

How Kotlin Works

How a Kotlin program is executed depends on the selected target platform.

For JVM development, the process typically looks like this:

• The developer writes source code in .kt files.
• The Kotlin compiler converts it into JVM bytecode.
• The resulting bytecode is executed by the JVM.
• The program interacts with the operating system and other components through the runtime environment.

For example, a service written in Kotlin can run on the same server environment that is already set up for Java applications.

In simplified form:

Kotlin → Compiler → JVM Bytecode → JVM → Operating System → Hardware

This allows Kotlin applications to use a significant part of the infrastructure originally created for Java.

Main Features of Kotlin

Kotlin was designed with the experience of developing in Java and other modern programming languages in mind. It allows many common programming constructs to be expressed more concisely and includes built-in mechanisms for preventing certain common errors.

Key features include:

• static typing;
• type inference;
• object-oriented and functional programming;
• built-in support for nullable and non-null types;
• coroutines;
• extension functions;
• data classes;
• smart casts;
• lambda expressions;
• Java interoperability on the JVM.

For example, the compiler flags an attempt to use a variable that may hold null while the code is still being compiled.

At the same time, Kotlin remains a separate programming language with its own syntax and set of features.

Kotlin vs. Java: What Is the Difference?

Kotlin and Java are separate programming languages, but on the JVM they use the same runtime environment and can be used within the same project.

The main differences are related to the languages themselves:

• Kotlin generally allows developers to write more concise code;
• null safety is built into Kotlin’s type system;
• Kotlin has built-in support for extension functions;
• the language provides coroutines for handling asynchronous operations;
• many common constructs require less boilerplate code.

For example, a data class takes a single line in Kotlin, while in Java the getters, setters, and other methods have to be written or generated as well.

Java, meanwhile, has its own actively evolving language model and a vast existing ecosystem.

The choice between them depends on the project, technologies being used, compatibility requirements, and the team’s experience.

Kotlin and Java Interoperability

One of the key features of Kotlin/JVM is Java interoperability, which allows the two languages to work together.

Kotlin code can use:

• Java classes;
• libraries;
• frameworks;
• interfaces;
• other components of the Java ecosystem.

For example, a new Kotlin module can call an existing Java library in the same project without any changes to it.

Java code can also access classes and functions written in Kotlin, although in some cases the way Kotlin constructs are represented on the JVM needs to be taken into account.

This interoperability makes it possible to migrate an existing Java project to Kotlin gradually without rewriting the entire application at once.

Advantages of Kotlin

The main advantages of Kotlin include:

• compatibility with Java;
• access to the existing JVM ecosystem;
• concise syntax;
• built-in null safety;
• coroutine support;
• the ability to introduce the language gradually into Java projects;
• use in Android and backend development;
• support for cross-platform development;
• the ability to compile for the JVM, JavaScript, and native platforms.

For example, a team can write new features in Kotlin and keep the existing Java code running unchanged.

This makes Kotlin suitable both for new projects and for use alongside an existing Java codebase.

Limitations of Kotlin

Choosing Kotlin also involves several considerations.

Depending on the project, it may be necessary to take into account:

• the additional language and toolset that the team needs to know;
• interoperability considerations when working with Java code;
• differences between JVM, Native, and JavaScript targets;
• dependencies on libraries and the target platform;
• the complexity of some multiplatform development scenarios.

For example, a required library may be available only for the JVM target and not for Kotlin/Native.

In addition, using Kotlin Multiplatform does not automatically eliminate all differences between operating systems and hardware platforms.

FAQ

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