--- title: Stop Using Java When Kotlin Exists | daily.dev description: Kotlin is presented as a compelling alternative to Java, given its full interoperability (same bytecode, same .class files) and ease of incremental adoption... canonical: https://daily.dev/posts/stop-using-java-when-kotlin-exists-ib2r2pgex twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Stop Using Java When Kotlin Exists | daily.dev og:description: Kotlin is presented as a compelling alternative to Java, given its full interoperability (same bytecode, same .class files) and ease of incremental adoption... og:url: https://daily.dev/posts/stop-using-java-when-kotlin-exists-ib2r2pgex og:image: https://api.daily.dev/og/posts/Ib2R2Pgex.png og:image:alt: Stop Using Java When Kotlin Exists og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Stop Using Java When Kotlin Exists **[Atomic Spin](https://daily.dev/sources/atomicobject)** · 5 min read · 34 upvotes · 8 comments ## Summary Kotlin is presented as a compelling alternative to Java, given its full interoperability (same bytecode, same .class files) and ease of incremental adoption within existing Java projects. The piece walks through Kotlin's advantages like coroutines, nullability handling, scoped functions, and companion objects, while also cautioning that writing idiomatic Kotlin differs meaningfully from Java, requiring teams to learn new patterns and watch for concurrency pitfalls. Interoperability with Java code can also dilute some benefits, such as null-safety guarantees. The author concludes that switching makes sense for most teams, especially new products or eager teams, with more detailed comparisons promised in future installments. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### Can I add Kotlin code to an existing Java project without rewriting everything? Yes, Kotlin can be added incrementally to an existing Java codebase with minimal effort. It compiles to the same bytecode as Java, producing identical .class files, so Kotlin binaries can be deployed alongside Java ones. Only a small amount of additional build configuration is needed to mix Java and Kotlin source files in the same project. _Developers weighing a gradual Kotlin migration follow practical interoperability guidance like this on daily.dev._ ### Do I lose Kotlin's null-safety benefits when calling into Java code? Yes, nullability information is lost whenever a call chain passes through Java code, since Java has no equivalent null-safety type system. This does not mean avoiding Kotlin, but it does mean the benefit is diminished in heavily mixed codebases. The more code that is migrated fully to Kotlin, the more of its null-safety guarantees are preserved. _Teams planning a Java-to-Kotlin migration track trade-offs like this on daily.dev before committing._ ## Community discussion Top comments from developers on daily.dev. **@maurizioturatti** · 10 upvotes > I'm working with large enterprise java codebases, ditching Java is not an option for me. Kotlin is indeed a wonderful language but since Java 21 I have found fewer and fewer reasons to move. Java is constantly evolving, at a much faster pace than ever. Besides, LLMs can be trained from a much larger codebase and documentation (blog posts, articles) than Kotlin, probably several orders of magnitude, and that makes AI-assisted development with Java extremely efficient (at least, in my experience). Said that, a startup should seriously evaluate Kotlin if starting fresh. However, I'd not... **@mikemacharia39** · 4 upvotes > I agree with you on this. Somehow I enjoy using Kotlin now more than Java because of it's simplicity. However, I would advise any dev to first learn Java before picking Kotlin. **@ahmetozel** · 0 upvotes > Incremental adoption is the strongest practical argument here, but I would start the migration with a clearly defined Java boundary rather than a scattered syntax conversion. Platform types from unannotated Java APIs can make a Kotlin value look safe until a null arrives at runtime. > > An adapter that converts those results into explicit nullable or non-null domain types gives the new code a reliable contract. Tests should include nulls in collections and callback results, not just a null return from one method. That makes the interoperability cost you describe measurable while allowing the... ## Similar posts on daily.dev - [Growing Kotlin Adoption in Your Company](https://daily.dev/posts/growing-kotlin-adoption-in-your-company-bvxxzvucx) · JetBrains · 1 upvotes · 0 comments - [Evaluating Kotlin in Real Projects](https://daily.dev/posts/evaluating-kotlin-in-real-projects-4hvtaptzn) · JetBrains · 4 upvotes · 0 comments - [Why Kotlin, Jetpack Compose, and Kotlin Multiplatform Succeeded: The Power of Incremental Adoption](https://daily.dev/posts/why-kotlin-jetpack-compose-and-kotlin-multiplatform-succeeded-the-power-of-incremental-adoption-zp4lwtskz) · Medium · 3 upvotes · 0 comments --- Tags: [#java](https://daily.dev/tags/java), [#spring](https://daily.dev/tags/spring), [#kotlin](https://daily.dev/tags/kotlin), [#jvm](https://daily.dev/tags/jvm) [View this post on daily.dev](https://daily.dev/posts/stop-using-java-when-kotlin-exists-ib2r2pgex) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"Stop Using Java When Kotlin Exists","url":"https://daily.dev/posts/stop-using-java-when-kotlin-exists-ib2r2pgex","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/stop-using-java-when-kotlin-exists-ib2r2pgex"},"datePublished":"2026-09-30T12:03:07.402Z","dateModified":"2026-09-30T12:03:29.150Z","description":"Kotlin is presented as a compelling alternative to Java, given its full interoperability (same bytecode, same .class files) and ease of incremental adoption...","image":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/936b4ddfe178f0aa06476d0e553bb957?_a=AQAEuop","thumbnailUrl":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/936b4ddfe178f0aa06476d0e553bb957?_a=AQAEuop","isAccessibleForFree":true,"articleSection":"Atomic Spin","inLanguage":"en","publisher":{"@type":"Organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180}},"author":{"@type":"Organization","name":"Atomic Spin","logo":"https://media.daily.dev/image/upload/t_logo,f_auto/v1/logos/e2af5ce3adaa403a8cf029268b62419f","url":"https://daily.dev/sources/atomicobject"},"commentCount":8,"discussionUrl":"https://daily.dev/posts/stop-using-java-when-kotlin-exists-ib2r2pgex","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":34},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":8}],"keywords":"java,spring,kotlin,jvm","timeRequired":"PT5M"} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"Atomic Spin","item":"https://daily.dev/sources/atomicobject"},{"@type":"ListItem","position":3,"name":"Stop Using Java When Kotlin Exists"}]} {"@context":"https://schema.org","@type":"WebPage","@id":"https://daily.dev/posts/stop-using-java-when-kotlin-exists-ib2r2pgex","comment":[{"@type":"Comment","text":"I’m working with large enterprise java codebases, ditching Java is not an option for me. Kotlin is indeed a wonderful language but since Java 21 I have found fewer and fewer reasons to move. Java is constantly evolving, at a much faster pace than ever. Besides, LLMs can be trained from a much larger codebase and documentation (blog posts, articles) than Kotlin, probably several orders of magnitude, and that makes AI-assisted development with Java extremely efficient (at least, in my experience). Said that, a startup should seriously evaluate Kotlin if starting fresh. However, I’d not recommend working with Kotlin without at least a good command of Java basics and JVM internals anyway.","datePublished":"2026-10-01T07:10:27.554Z","url":"https://daily.dev/posts/Ib2R2Pgex#c-Fr95iaO4o","author":{"@type":"Person","name":"Maurizio Turatti","url":"https://daily.dev/maurizioturatti","image":"https://avatars.githubusercontent.com/u/365382?v=4"},"interactionStatistic":{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":10}},{"@type":"Comment","text":"I agree with you on this. Somehow I enjoy using Kotlin now more than Java because of it’s simplicity. However, I would advise any dev to first learn Java before picking Kotlin.","datePublished":"2026-09-30T18:43:11.632Z","url":"https://daily.dev/posts/Ib2R2Pgex#c-1dkfvTTYH","author":{"@type":"Person","name":"Mikehenry","url":"https://daily.dev/mikemacharia39","image":"https://avatars.githubusercontent.com/u/15307122?v=4"},"interactionStatistic":{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":4}},{"@type":"Comment","text":"Incremental adoption is the strongest practical argument here, but I would start the migration with a clearly defined Java boundary rather than a scattered syntax conversion. Platform types from unannotated Java APIs can make a Kotlin value look safe until a null arrives at runtime.\nAn adapter that converts those results into explicit nullable or non-null domain types gives the new code a reliable contract. Tests should include nulls in collections and callback results, not just a null return from one method. That makes the interoperability cost you describe measurable while allowing the rest of the Java application to continue unchanged.","datePublished":"2026-10-06T18:22:50.043Z","url":"https://daily.dev/posts/Ib2R2Pgex#c-JeXWzeQYm","author":{"@type":"Person","name":"Ahmet Özel","url":"https://daily.dev/ahmetozel","image":"https://avatars.githubusercontent.com/u/70992231?v=4"}}]} {"@context":"https://schema.org","@type":"FAQPage","@id":"https://daily.dev/posts/stop-using-java-when-kotlin-exists-ib2r2pgex#faq","mainEntity":[{"@type":"Question","name":"Can I add Kotlin code to an existing Java project without rewriting everything?","acceptedAnswer":{"@type":"Answer","text":"Yes, Kotlin can be added incrementally to an existing Java codebase with minimal effort. It compiles to the same bytecode as Java, producing identical .class files, so Kotlin binaries can be deployed alongside Java ones. Only a small amount of additional build configuration is needed to mix Java and Kotlin source files in the same project. Developers weighing a gradual Kotlin migration follow practical interoperability guidance like this on daily.dev."}},{"@type":"Question","name":"Do I lose Kotlin's null-safety benefits when calling into Java code?","acceptedAnswer":{"@type":"Answer","text":"Yes, nullability information is lost whenever a call chain passes through Java code, since Java has no equivalent null-safety type system. This does not mean avoiding Kotlin, but it does mean the benefit is diminished in heavily mixed codebases. The more code that is migrated fully to Kotlin, the more of its null-safety guarantees are preserved. Teams planning a Java-to-Kotlin migration track trade-offs like this on daily.dev before committing."}}]} ```