How to call functions in a native library via the JNI interface

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The Java Native Interface (JNI) allows you to call native functions from Java code, and vice versa. This example shows how to load and call a native function via JNI, it does not go into accessing Java methods and fields from native code using JNI functions.

Suppose you have a native library named libjniexample.so in the project/libs/<architecture> folder, and you want to call a function from the JNITestJava class inside the com.example.jniexample package.

In the JNITest class, declare the function like this:

public native int testJNIfunction(int a, int b);

In your native code, define the function like this:

#include <jni.h>

JNIEXPORT jint JNICALL Java_com_example_jniexample_JNITest_testJNIfunction(JNIEnv *pEnv, jobject thiz, jint a, jint b)
{
    return a + b;
}

The pEnv argument is a pointer to the JNI environment that you can pass to JNI functions to access methods and fields of Java objects and classes. The thiz pointer is a jobject reference to the Java object that the native method was called on (or the class if it is a static method).

In your Java code, in JNITest, load the library like this:

static{
    System.loadLibrary("jniexample");
}

Note the lib at the start, and the .so at the end of the filename are omitted.

Call the native function from Java like this:

JNITest test = new JNITest();
int c = test.testJNIfunction(3, 4);

Found a mistake? Have a question or improvement idea? Let me know.

Android NDK:

* Android NDK

* How to log in ndk

* Building native executables for Android

* How to call functions in a native library via the JNI interface

* How to clean the build

* How to use a makefile other than Android.mk

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0 Getting Started

1 Layouts

2 Gradle

3 RecyclerView onClickListeners

4 NavigationView

5 Intent

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58 The Manifest File

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62 Data Synchronization with Sync Adapter

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74 In-app billing

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76 ContentProvider

77 Dagger 2

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79 Unit testing in Android with JUnit

80 Android Versions

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87 Google Awarness APIs

88 Text to Speech (TTS)

89 UI Lifecycle

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92 Testing UI with Espresso

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95 OkHttp

96 Enhancing Performance Using Icon Fonts

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102 Facebook SDK

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104 Android Places API

105 Creating your own libraries

106 Handling JSON with Gson

107 Device Display Metrics

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110 Building Backwards Compatible Apps

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112 ProGuard - Obfuscating and Shrinking your code

113 Detect Shake Event

114 Typedef Annotations

115 Capturing Screenshots

116 MVP Architecture

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153 Firebase Crash Reporting

154 Displaying Google Ads

155 Vk SDK

156 Localized DateTime

157 Count Down Timer

158 Reading Barcode and QR codes

159 Otto Event Bus

160 TransitionDrawable

161 Port Mapping using Cling

162 Creating Overlay always-on-top Windows

163 ExoPlayer

164 Inter-app UI testing with UIAutomator

165 MediaSession

166 Speech to Text Conversion

167 FileProvider

168 Publish .aar file to Apache Archive with Gradle

169 XMPP

170 Authenticator

171 RecyclerView and LayoutManagers

172 AudioManager

173 Job Scheduling

174 Accounts and AccountManager

175 OpenCV

176 Split Screen Multi-Screen Activities

177 Threads

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179 Time Utils

180 Touch Events

181 Fingerprint API

182 MVVM Architecture

183 BottomNavigationView

184 ORMLite

185 YouTube API

186 TabLayout

187 Retrofit2 with RxJava

188 DayNight Theme AppCompat

189 ShortcutManager

190 LruCache

191 Using Jenkins CI

192 Zip files

193 Vector Drawables

194 Fastlane

195 Define step value for RangeSeekBar

196 Getting started with OpenGL ES 2.0

197 Check Data Connection

198 Java Native Interface (JNI)

199 FileIO

200 Perfomance Optimization

201 Robolectric

202 Moshi

203 Strick Mode Policy

204 Internalization and localization

205 Retrolambda

206 SparseArray

207 Firebase Cloud Messaging

208 Shared Element Transitions

209 Android Things

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212 Dependency Injection with Dagger 2

213 Formatting phone numbers

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215 Android Kernel Optimization

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219 Create Android Custom ROMs

220 Java on Android

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222 Genymotion for Android

223 Handling touch and motion events

224 Creating Splash screen

225 ConstraintSet

226 CleverTap

227 Publish library to Maven repositories

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229 Ping ICMP

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231 Using Kotlin

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233 Signing apps for release

234 Context

235 Activity Recognition

236 Secure SharedPreferences

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238 Bitmap Cache

239 Android x86 in VirtualBox

240 JCodec

241 Design Patterns

242 Okio

243 Google SignIn integration

244 TensorFlow

245 Game developmen

246 Notification Channel

247 Bluetooth Low Energy (LE)

248 Leak Canary

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250 SQLite using ContentValues

251 Enhancing Alert Dialogs

252 Hardware Button Events, Intents PTT

253 SpannableString

254 Looper

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256 Google Drive API

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258 Annotation Processor

259 SyncAdapter with periodically do sync of data

260 Singleton Class for Toast Message

261 Fastjson

262 Android Architecture Components

263 Jackson

264 Play Store

265 Loading Bitmaps Effectively

266 Getting system font names

267 Smartcard

268 Convert vietnamese string to english

269 Contributors