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JNI short tutorial

Create a Java class to use code in C

1 Write a Java class that uses C codes

CraftJNI.java
public class CraftJNI {
  static {
    System.loadLibrary("hello"); // Load native library hello.dll (windows)
                                 // or libhello.so (Unixes) at runtime.
                                 // This library contains a native method sayHello()
                                 
  }
  
  // Declare an instance native method sayHello() which receives no parameter
  // returns void
  private native void sayHello();
  
  // Test Driver
  public static void main(String[] args) {
    new CraftJNI().sayHello(); // Create an instance and invoke native method
  }
}

2 Compile Java program CraftJNI.java

To know more about the generated class file

3 Implement C program

4 Compile C program

Troubleshooting

Error 1: class file has wrong version

Reason: javah is not available with Java 11

Error 2:

References

  1. JNI reference docs - https://docs.oracle.com/javase/8/docs/technotes/guides/jni/spec/jniTOC.html

  2. Some of the code is shamelessly copied from https://www3.ntu.edu.sg/home/ehchua/programming/java/JavaNativeInterface.html

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