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Java / JVM Architecture (Java21) Interview questions

What is the purpose of the Java Native Interface (JNI)?

The Java Native Interface (JNI) lets Java code call functions written in native languages like C or C++, and lets native code call back into Java objects and methods.

It is used when an application needs to reach platform-specific APIs the JDK does not expose, reuse an existing native library, or hand off performance-critical work to hand-tuned native code.

The trade-off is that JNI calls cross a real boundary: they bypass some JVM safety guarantees, add per-call overhead, and a native crash can bring down the whole JVM process instead of throwing a catchable exception.

Java 21 also ships the Foreign Function & Memory API (JEP 442, a preview feature) as a safer, easier-to-use alternative for calling native code without writing JNI glue code.

JNI is typically used to:
A risk of using JNI is that:

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