JNI Basics

From Weiss's C++ for Java Programmers Initial Code:

To run the code

Compile the Java Code
```
     javac HelloNativeTest.java
```
This creates two .class files: HelloNativeTest.class, HelloNative.class
The HelloNative.class file is used to create the proper .h file for the C++ code by using the command of:
```
     javah HelloNative
```

Now to compile the C++ code (shown using UNIX commands):

    # g++ -c -fPIC -I$JAVA_HOME/include -I$JAVA_HOME/include/linux HelloNative.cpp
    g++ -c -fPIC HelloNative.cpp

This create the HelloNative.o file.

Now create the shared library object file with the command:
```
    g++ -shared -o libHelloNative.so HelloNative.o
```
Before running the program the java code has to know where the shared library file is located so it can be loaded, so we need to set the LD_LIBRARY_PATH environment variable to its locations. The command below assumes the file is in the current directory.
```
     setenv LD_LIBRARY_PATH .
```
Now to run the java program with
```
     java HelloNativeTest
```

Other Examples from Weiss