add jni

jni/HelloWorld.java

@@ -0,0 +1,18 @@
+public class HelloWorld {
+    // This declares that the static `hello` method will be provided
+    // a native library.
+    private static native String hello(String input);
+
+    static {
+        // This actually loads the shared object that we'll be creating.
+        // The actual location of the .so or .dll may differ based on your
+        // platform.
+        System.loadLibrary("samplejni");
+    }
+
+    // The rest is just regular ol' Java!
+    public static void main(String[] args) {
+        String output = HelloWorld.hello("josh");
+        System.out.println(output);
+    }
+}