Work with the Java method

Question

I am new to java and am currently learning my own methods when I create the following files:

Main.java

public class Main {
    public native int intMethod(int i);
    public static void main(String[] args) {
        System.loadLibrary("Main");
        System.out.println(new Main().intMethod(2));
    }
}

main.c

#include <jni.h>
#include "Main.h"

JNIEXPORT jint JNICALL Java_Main_intMethod(
    JNIEnv *env, jobject obj, jint i) {
  return i * i;
}

Compile and run :

javac Main.java
javah -jni Main
gcc -shared -fpic -o libMain.so -I${JAVA_HOME}/include \
  -I${JAVA_HOME}/include/linux Main.c
java -Djava.library.path=. Main

Exit

4

But when I do this:

troller.java

public class troller {
    public native int intMethod(int i);
    public static void main(String[] args) {
        System.loadLibrary("troller");
        System.out.println(new troller().intMethod(2));
    }
}

troller.c

#include <jni.h>
#include "troller.h"

JNIEXPORT jint JNICALL Java_Main_intMethod(
    JNIEnv *env, jobject obj, jint i) {
  return i * i;
}

Compile and run :

javac troller.java
javah -jni troller
gcc -shared -fpic -o libMain.so -I${JAVA_HOME}/include \
  -I${JAVA_HOME}/include/linux Main.c
java -Djava.library.path=. troller

Exit

Exception in thread "main" java.lang.UnsatisfiedLinkError: no troller in java.library.path
at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1886)
at java.lang.Runtime.loadLibrary0(Runtime.java:849)
at java.lang.System.loadLibrary(System.java:1088)
at troller.main(troller.java:4)

Why does the program stop working if I change the name?

EDIT : After examining the answers, I noticed some inconsistencies and now recreated all the files, but the error persists: Native.java

public class Native{
public native int intMethod(int i);
public static void main(String[] args){S
    System.loadLibrary("Native");
    System.out.println("In java... :)");
    System.out.println(new Native().intMethod(4));

}
}

Native.c

#include<jni.h>
#include"Native.h"

JNIEXPORT jint JNICALL Java_Native_intMethod(
JNIEnv *env, jobject obj, jint i){
printf("In C .... :)");
return i*i;
}

compile and run

javac Native.java 
javah -jni Native
gcc -shared -fpic -o libMain.so -I${JAVA_HOME}/include  \
 -I${JAVA_HOME}/include/linux Native.c
java -Djava.library.path=. Native
Exception in thread "main" java.lang.UnsatisfiedLinkError: no Native in java.library.path
at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1886)
at java.lang.Runtime.loadLibrary0(Runtime.java:849)
at java.lang.System.loadLibrary(System.java:1088)
at Native.main(Native.java:4)

Answer 1

When you create a stub .hfor your own methods using javah, it includes the name of the class and class. This means that you can have the same method name in different classes.

Java_Main_intMethod

Java_troller_intMethod

, , .

. C @Override, , .h.;)

Answer 2

Main to Troller, . - libMain.so. , , , .

C troller.c, gcc , .

Answer 3

Java- , .

-I ${JAVA_HOME}/include/linux Main.c

, troller.c Main.c