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Calling a C Function from the Java Programming Language using JNI
  • Suppose you have sample c code which do some use full function and you don’t like to implement it in java again.
  • The solution is java native interface (JNI). It let you to invoke C/C++ function within the java code.
  • Suppose this is the C function u need to invoke.
        void greeting()
            printf("Hello Native World!\n");
  • But before it used in java this c code should be define as native method.
  • For eases of use let’s define the how we going to use this function in java.
        class HelloNative{
            public static native void greeting();
  • HellowNative is like interface in java. Then JVM load the native library when it use this class.
  • To use HelloNative.java "HelloNative" native library should be compatible with HelloNative.java. To implement compatible library we implement compatible C file.
  • To do this we generate header file based on this.
  • Compile the HelloNative.java
        javac HelloNative.java
  • Generate header
        javah HelloNative
  • Implement the C function
        #include "HelloNative.h"
        JNIEXPORT void JNICALL Java_HelloNative_greeting (JNIEnv *env, jclass cl)
            printf("Hello Native World!\n");
  • Generate Linkied library
        //on Cygwin programming environment in windows
        gcc -mno-cygwin -D __int64="long long" -I JAVA_HOME/include/ -I JAVA_HOME/include/win32 -shared -Wl,--add-stdcall-alias -o HelloNative.dll HelloNative.c
        // Gnu C compiler on Linux
        gcc -fPIC -I JAVA_HOME/include -I JAVA_HOME/include/linux -shared -o libHelloNative.so HelloNative.c
        //With tSun compiler under the Solaris Operating System
        cc -G -I JAVA_HOME/include -I JAVA_HOME/include/solaris -o libHelloNative.so HelloNative.c
        //in Microsoft C++ compiler on Windows
        cl -I JAVA_HOME\include -I JAVA_HOME\include\win32 -LD HelloNative.c -FeHelloNative.dll
  • Implement the test class
        class HelloNativeTest{
            public static void main(String[] args){
  • Run the test class
        javac HelloNativeTest.java
        java HelloNativeTest
  • Get the source code here.

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