Does Kotlin Compile Faster Than Java? Real‑World Benchmark Results

In this article the author investigates how long it takes to compile a Java application after converting it to Kotlin, addressing common concerns about Kotlin's compilation speed.

How I Test Build Time

A shell script repeatedly runs Gradle ten times for each scenario, cleaning the project before each run and using the Gradle daemon where appropriate. All tests were performed on a 3.4 GHz Intel Core i7‑6700 with 32 GB DDR4 RAM and a Samsung 850 Pro SSD. The source was built with Gradle 2.14.1.

Test Scenarios

The benchmarks cover three typical usage patterns:

Clean build without the Gradle daemon.

Clean build with the Gradle daemon.

Incremental builds: no file changes, a changed file that is not imported elsewhere, and a changed file that is imported by many other files.

Clean Build + No Daemon

In the worst‑case cold‑start scenario (clean build, daemon disabled), the average times were 15.5 seconds for Java and 18.5 seconds for Kotlin, a 17 % slowdown for Kotlin.

Without the Gradle daemon and a clean build, Java compiles 17 % faster than Kotlin.

Clean Build + Gradle Daemon

When the Gradle daemon is enabled, the first run matches the no‑daemon time, but subsequent runs are faster. After the daemon has warmed up, the average clean‑build times are 14.1 seconds for Java and 16.5 seconds for Kotlin, a 13 % slowdown for Kotlin.

With a clean build and the Gradle daemon, Java compiles 13 % faster than Kotlin.

Regardless of language, the daemon reduces build time by more than 40 %.

Incremental Builds

Incremental compilation recompiles only changed files and their dependents. Kotlin supports incremental compilation since version 1.0.2 (enable with kotlin.incremental=true in gradle.properties).

Benchmark results for incremental builds:

No file changes: Java 4.6 s, Kotlin 4.5 s (Kotlin slightly faster).

Change a file not used elsewhere: Java 7.0 s, Kotlin 6.1 s (Kotlin faster).

Change a file imported by many others: Java 7.1 s, Kotlin 6.0 s (Kotlin faster).

In the most common case—partial builds with incremental compilation—Kotlin compiles as fast as or slightly faster than Java.

Conclusion

The benchmarks show that while Java is 10‑15 % faster on cold clean builds, these situations are rare. For typical development workflows that rely on incremental builds and the Gradle daemon, Kotlin’s compilation speed matches or even exceeds Java’s.

This result is impressive and demonstrates that Kotlin’s design delivers both powerful language features and competitive compile performance.

Original article: Kotlin vs Java Compilation Speed