Why Java 22?

Java 22 introduces the Foreign Function and Memory API (FFM API), a modern alternative to the legacy Java Native Interface (JNI). JNI was traditionally used to interact with C-like functions and data types in external libraries. However, JNI is cumbersome, error-prone, and introduces significant overhead due to repeated native function calls and lack of Just-In-Time (JIT) optimizations. Java objects needed to be passed through JNI, requiring additional work on the native side to identify object types and data locations, making the entire process tedious and slow. With the FFM API, Java now pushes much of the integration work to the Java side, eliminating the need for custom C headers and providing more visibility for the JIT compiler.

This change leads to Better Performance, as the JIT compiler can now optimize calls to native libraries more effectively. It also leads to Simplified Integration because there are fewer requirements on native function signatures. This reduces the overhead of native-to-Java translation. Additionally, the API provides Enhanced Flexibility, as it supports working with various languages like Rust while maintaining full control over how memory and function calls are handled.

Java 22 is the first version to stabilize this API, making it the ideal choice for this manual. It enables efficient, direct interaction with Rust libraries without the historical drawbacks of JNI.