> Markdown version of [/videos/384-moving-from-java-to-kotlin?t=961](https://www.wearedevelopers.com/videos/384-moving-from-java-to-kotlin?t=961). Every page supports `.md` or `Accept: text/markdown`. Links point to the HTML versions so they work for humans too. Agent guide: [/agents.md](https://www.wearedevelopers.com/agents.md).

---

# Moving from Java to Kotlin

Tired of Java boilerplate and unpredictable null pointer exceptions? Discover how migrating to Kotlin can shrink your codebase by 40% while maintaining complete interoperability with existing tools.

- **Speakers:** Urs Peter
- **Event:** World Congress 2022
- **Published:** June 15, 2022
- **Duration:** 28:22
- **URL:** https://www.wearedevelopers.com/videos/384-moving-from-java-to-kotlin

## Summary

Transitioning from Java to Kotlin addresses longstanding verbosity and safety shortcomings in the Java ecosystem while maintaining complete interoperability with existing tools like Maven, Gradle, and Spring Boot. By elevating functions to first-class citizens and condensing boilerplate—combining fields, getters, setters, and constructors into unified primary constructors and data classes—Kotlin significantly reduces code volume. Developers can build highly expressive, idiomatic applications using lightweight syntax, default arguments, and infix methods that naturally mimic domain-specific languages.

Crucial safety and quality-of-life enhancements stem from Kotlin's type-level null safety and smart casting, effectively eliminating unpredictable null pointer exceptions without relying on cumbersome wrapper classes like `Optional`. The language further simplifies daily engineering tasks through extension functions, offering seamless utility for API interactions, I/O operations, and collections that treat immutability as the default. Additionally, Kotlin coroutines revolutionize system concurrency; they empower developers to write high-performance, non-blocking asynchronous logic sequentially, entirely sidestepping the cognitive overhead and complex combinators required by traditional reactive frameworks.

From a technical management perspective, migrating to Kotlin delivers a swift return on investment, typically realized within two to four months due to an estimated 40% reduction in codebase size and sharply decreased bug rates. Organizations can pursue a risk-averse, gradual adoption path by first leveraging IDE auto-converters to transition test suites and JPA domain entities before attempting full microservices. By investing in targeted in-house training and defining clear roadmaps for hybrid Java-Kotlin architectures, engineering leaders can preserve their current framework knowledge while unlocking massive gains in code clarity and developer satisfaction.

**Keywords:** java to kotlin migration, jvm language interoperability, kotlin primary constructors, data classes vs java records, type-level null safety, kotlin smart casting, extension functions, immutable collections by default, kotlin coroutines, reactive programming alternatives, spring boot kotlin integration, jpa entity refactoring, legacy codebase modernization, intellij java converter, developer productivity roi

## Chapters

1. **Introduction to Kotlin history and Java ecosystem interoperability** (00:05) — How careful language design decisions enable seamless interoperability with the existing Java ecosystem.
1. **Condensing object-oriented boilerplate code with primary constructors** (03:08) — Combining field declarations and primary constructors reduces typical object-oriented boilerplate while maintaining instantiation safety.
1. **Simplifying functional programming capabilities with first-class functions** (06:50) — Treating functions as first-class citizens removes the necessity of managing cumbersome single-method functional interfaces.
1. **Implementing type-level null safety and smart casting** (08:16) — Enforcing strict nullability rules at the compiler level eliminates unexpected runtime exceptions during data operations.
1. **Eliminating utility classes by leveraging custom extension functions** (10:48) — Attaching custom operations to external classes directly eliminates the need for abstracted utility files.
1. **Creating expressive testing domain specific languages with infix functions** (12:32) — Using specialized syntax to omit standard calling conventions enables developers to construct readable unit test assertions.
1. **Working with immutable collections and data structure transformations** (13:06) — Default immutability paradigms and concise standard library transformations make data list processing robust and predictable.
1. **Simplifying asynchronous concurrency patterns safely with coroutines logic** (16:01) — Coroutines execute complex asynchronous procedures sequentially without requiring teams to rely heavily on dense reactive toolkits.
1. **Analyzing business benefits and return on investment metrics** (19:27) — Strategic developer education yields rapid returns on investment through significantly reduced defect rates and concise maintainability.
1. **Practical strategies for migrating an existing Java codebase** (21:52) — Converting standard application tests and domains sequentially ensures continuous operational functionality remains stable during syntax migration.
1. **Scaling idiomatic usage models and internal developer training** (26:57) — Establishing clear migration roadmaps and coaching prevents anti-patterns and encourages engineers to write truly idiomatic syntax.

## Related Moments

- [Introduction to Kotlin and Java interoperability](https://www.wearedevelopers.com/videos/512-route-from-java-to-kotlin) (from "Route from Java to Kotlin")
- [Summarizing the practical engineering advantages of writing Kotlin](https://www.wearedevelopers.com/videos/661-why-kotlin-is-the-better-java-and-how-you-can-start-using-it) (from "Why Kotlin is the better Java and how you can start using it")
- [Introduction to the Java and Kotlin ecosystems](https://www.wearedevelopers.com/videos/661-why-kotlin-is-the-better-java-and-how-you-can-start-using-it) (from "Why Kotlin is the better Java and how you can start using it")
- [Configuring runtime Java and Kotlin interoperability protocols](https://www.wearedevelopers.com/videos/661-why-kotlin-is-the-better-java-and-how-you-can-start-using-it) (from "Why Kotlin is the better Java and how you can start using it")
- [Recommended resources and frameworks for learning Kotlin natively](https://www.wearedevelopers.com/videos/661-why-kotlin-is-the-better-java-and-how-you-can-start-using-it) (from "Why Kotlin is the better Java and how you can start using it")
- [Key takeaways and future Kotlin Multiplatform improvements](https://www.wearedevelopers.com/videos/4-kotlin-multiplatform-true-power-of-native-code-reuse) (from "Kotlin Multiplatform - True power of native code reuse")

## Related Articles

- [Using Java 17 latest features in real world projects](https://www.wearedevelopers.com/magazine/121-using-java-17-latest-features-in-real-world-projects)
- [Modern Java Records](https://www.wearedevelopers.com/magazine/41-modern-java-records)
- [Modern Java Switch Expressions](https://www.wearedevelopers.com/magazine/40-modern-java-switch-expressions)
- [Top in-demand programming languages to learn in 2021](https://www.wearedevelopers.com/magazine/30-top-in-demand-programming-languages-to-learn-in-2021)

## Related Jobs

- [Senior Software Engineer, Android (Earn Experience)](https://www.wearedevelopers.com/jobs/ext/1937627-senior-software-engineer-android-earn-experience) at **Bitpanda**
- [Java Softwareentwickler Migrationsprojekte (m/w/d)](https://www.wearedevelopers.com/jobs/48138-java-softwareentwickler-migrationsprojekte-m-w-d) at **Finanz Informatik**
- [Lead Software Engineer (f/m/d)](https://www.wearedevelopers.com/jobs/48296-lead-software-engineer-f-m-d) at **Personio SE & Co. KG**
- [Senior Backend Engineer (Java)](https://www.wearedevelopers.com/jobs/ext/19369-senior-backend-engineer-java) at **Bonial International GmbH**
- [Softwareentwickler Java](https://www.wearedevelopers.com/jobs/ext/1245896-softwareentwickler-java) at **Aok Systems Gmbh**
- [Softwareentwickler Künstliche Intelligenz mit Schwerpunkt Projektkoordination](https://www.wearedevelopers.com/jobs/ext/1247541-softwareentwickler-kunstliche-intelligenz-mit-schwerpunkt-projektkoordination) at **Aok Systems Gmbh**