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A modern, concise language for JVM and Android development. Fully interoperable with Java.
JetBrains unveiled Kotlin in 2011 and released version 1.0 in 2016, designing it as a pragmatic, concise alternative to Java that maintains full interoperability with existing JVM code. Google endorsed Kotlin as the preferred language for Android development in 2019, rapidly accelerating its adoption across the mobile ecosystem. Kotlin eliminates much of Java's verbosity — null safety is built into the type system, data classes auto-generate equals/hashCode/toString, and extension functions allow adding methods to existing classes without inheritance. The language supports coroutines as a first-class feature for asynchronous programming, providing structured concurrency that is lighter and more intuitive than Java's thread-based model.
Kotlin Multiplatform (KMP) enables sharing business logic across Android, iOS, desktop, and web targets from a single codebase, with Compose Multiplatform extending UI sharing beyond Android. On the server side, Kotlin works seamlessly with Spring Boot, Ktor (JetBrains' own framework), and Micronaut. Kotlin/JS compiles to JavaScript for web development, and Kotlin/Native produces binaries for platforms without a JVM. The Kotlin DSL for Gradle has become the recommended way to write build scripts, replacing Groovy in many projects.
Kotlin's type system includes sealed classes, inline classes, and reified generics that provide capabilities beyond what Java offers. The language follows a pragmatic evolution philosophy, adding features like context receivers, value classes, and K2 compiler improvements while maintaining backward compatibility.
Kotlin's concise syntax can pack significant logic changes into small diffs, making careful comparison essential. Comparing files catches modified null-safety operators that change crash behavior, altered coroutine scope configurations that affect lifecycle management, changed data class properties that break serialization contracts, and updated Kotlin DSL build scripts that modify dependency resolution.
Teams diff shared KMP modules with special attention, as changes affect Android, iOS, and backend targets simultaneously.
UtraDiff compares Kotlin files with Kotlin syntax highlighting, covering data classes, coroutines, extension functions, and sealed interfaces. Side-by-side view aligns class hierarchies and when-expression branches across panels. The whitespace ignore toggle filters out ktlint reformatting changes.
Alt+Arrow navigation jumps between modified functions. Language-aware tokenization distinguishes annotation changes from code logic, making Compose UI and Gradle KTS diffs easy to review.
Supported extensions: .kt .kts