Using NDK for Performance - Dalvik Versus Native

package com.marakana;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class Fibonacci extends Activity implements OnClickListener {
  TextView textResult;
  Button buttonGo;
  EditText editInput;

  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    // Find UI views
    editInput = (EditText) findViewById(R.id.editInput);
    textResult = (TextView) findViewById(R.id.textResult);
    buttonGo = (Button) findViewById(R.id.buttonGo);
    buttonGo.setOnClickListener(this);
  }

  public void onClick(View view) {
    int input = Integer.parseInt(editInput.getText().toString());
    long start, stop;
    int result;
    String out = "";

    // Dalvik - Recursive
    start = System.currentTimeMillis();
    result = FibLib.fibJ(input);
    stop = System.currentTimeMillis();
    out += String.format("Dalvik recursive: %d (%d msec)", result, stop - start);

    // Dalvik - Iterative
    start = System.currentTimeMillis();
    result = FibLib.fibJI(input);
    stop = System.currentTimeMillis();
    out += String.format("\nDalvik iterative: %d (%d msec)", result, stop - start);

    // Native - Recursive
    start = System.currentTimeMillis();
    result = FibLib.fibN(input);
    stop = System.currentTimeMillis();
    out += String.format("\nNative recursive: %d (%d msec)", result, stop - start);

    // Native - Iterative
    start = System.currentTimeMillis();
    result = FibLib.fibNI(input);
    stop = System.currentTimeMillis();
    out += String.format("\nNative iterative: %d (%d msec)", result, stop - start);

    textResult.setText(out);
  }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:orientation="vertical" android:layout_width="fill_parent"
  android:layout_height="fill_parent" android:gravity="center_horizontal">
  <TextView android:layout_width="fill_parent"
    android:layout_height="wrap_content" android:text="@string/app_name"
    android:gravity="center" android:textSize="40sp"
    android:layout_margin="10dp" />
  <LinearLayout android:layout_width="wrap_content"
    android:layout_height="wrap_content">
    <EditText android:layout_width="wrap_content"
      android:layout_height="wrap_content" android:id="@+id/editInput"
      android:hint="Input" android:textSize="30sp" android:inputType="number"
      android:layout_margin="10dp"></EditText>
    <Button android:layout_width="wrap_content"
      android:layout_height="wrap_content" android:id="@+id/buttonGo"
      android:text="Go" android:textSize="30sp" android:layout_margin="10sp"></Button>
  </LinearLayout>
  
  <TextView android:layout_width="wrap_content"
    android:layout_height="wrap_content" android:id="@+id/textResult"
    android:text="RESULT" android:textSize="20sp"></TextView>

</LinearLayout>

package com.marakana;

public class FibLib {

  // Java implementation - recursive
  public static int fibJ(int n) {
    if (n <= 0)
      return 0;
    if (n == 1)
      return 1;
    return fibJ(n - 1) + fibJ(n - 2);
  }

  // Java implementation - iterative
  public static int fibJI(int n) {
    int previous = -1;
    int result = 1;
    for (int i = 0; i <= n; i++) {
      int sum = result + previous;
      previous = result;
      result = sum;
    }
    return result;
  }

  // Native implementation
  static {
    System.loadLibrary("fib");
  }

  // Native implementation - recursive
  public static native int fibN(int n);

  // Native implementation - iterative
  public static native int fibNI(int n);
}

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class com_marakana_FibLib */

#ifndef _Included_com_marakana_FibLib
#define _Included_com_marakana_FibLib
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     com_marakana_FibLib
 * Method:    fibN
 * Signature: (I)I
 */
JNIEXPORT jint JNICALL Java_com_marakana_FibLib_fibN
  (JNIEnv *, jclass, jint);

/*
 * Class:     com_marakana_FibLib
 * Method:    fibNI
 * Signature: (I)I
 */
JNIEXPORT jint JNICALL Java_com_marakana_FibLib_fibNI
  (JNIEnv *, jclass, jint);

#ifdef __cplusplus
}
#endif
#endif

#include "com_marakana_FibLib.h"


jint fibN(jint n) {
  if(n<=0) return 0;
  if(n==1) return 1;
  return fibN(n-1) + fibN(n-2);
}

jint fibNI(jint n) {
  jint previous = -1;
  jint result = 1;
  jint i=0;
  jint sum=0;
  for (i = 0; i <= n; i++) {
    sum = result + previous;
    previous = result;
    result = sum;
  }
  return result;
}

JNIEXPORT jint JNICALL Java_com_marakana_FibLib_fibN
  (JNIEnv *env, jclass obj, jint  n) {
  return fibN(n);
}

JNIEXPORT jint JNICALL Java_com_marakana_FibLib_fibNI
  (JNIEnv *env, jclass obj, jint  n) {
  return fibNI(n);
}

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)

LOCAL_MODULE    := fib
LOCAL_SRC_FILES := fib.c

include $(BUILD_SHARED_LIBRARY)