Return to Java, Foreign Function Interface (FFI)

Java Native Interface (JNI) is a framework that enables Java code running in the Java Virtual Machine (JVM) to interact with applications and libraries written in other languages, primarily C, C++, and assembly. JNI allows Java code to call native methods and vice versa, facilitating interoperability between Java and native code.

• **Calling Native Methods:** Java code can invoke functions implemented in native libraries using JNI. This allows Java to access platform-specific features or leverage existing native code.
• **Embedding JVM:** Native applications can embed the JVM, allowing them to execute Java code and access Java libraries.
• **Data Exchange:** JNI provides mechanisms for exchanging data between Java and native code, including primitive types, objects, arrays, and strings.
• **Exception Handling:** JNI allows exceptions thrown in Java code to be caught and handled in native code, and vice versa.
• **Reflection:** JNI provides limited reflection capabilities, allowing native code to inspect and manipulate Java classes and objects.

• **Oracle Documentation:** s://docs.oracle.com/en/java/javase/17/docs/specs/jni/index.html(https://docs.oracle.com/en/java/javase/17/docs/specs/jni/index.html)

**Java (Calling Native Method):**

```java public class Example {

   // Declare a native method
   private native void sayHello();

   static {
       // Load the native library
       System.loadLibrary("example");
   }

   public static void main(String[] args) {
       new Example().sayHello();
   }

**C (Implementing Native Method):**

```c

1. include <jni.h>
2. include <stdio.h>

JNIEXPORT void JNICALL Java_Example_sayHello(JNIEnv *env, jobject obj) {

   printf("Hello from C!\n");

In this example, the Java code declares a native method `sayHello` and loads a native library named `example`. The C code implements this method, which simply prints a message to the console.