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官方实例：android ubuntu ndk jni hello-jni

分类: 文章 • 2022-11-10 00:20:28

这里我贴一下其它网友有关为什么用jni的原因：

  1. 你的Java代码，需要得到一个文件的属性。但是你找遍了JDK帮助文档也找不到相关的API。
  2. 在本地还有一个别的系统，不过他不是Java语言实现的，这个时候你的老板要求你把两套系统整合到一起。
  3. 你的Java代码中需要用到某种算法，不过算法是用C实现并封装在动态链接库文件（DLL）当中的。

参考资料：http://developer.android.com/sdk/ndk/index.html 、http://developer.android.com/sdk/ndk/overview.html

下 载android-ndk-r6-linux-x86.tar.bz2然后解压，那个解压后会有个README.txt文件大概对doc包下的一些说明文档进行了粗略的介绍，那个文档中有下面的指导，所以需要认真的看一下。


本地操作：

[email protected]:~$ pwd
/home/pateo
[email protected]:~$ gedit .bashrc

在文件中输入的内容：

export NDK_HOME=/home/pateo/work/android-ndk-r6
export PATH=$PATH:$NDK_HOME

然后保存

[email protected]:~$ source .bashrc

[email protected]:~$ echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/home/pateo/work/android-ndk-r6

[email protected]:~$ cd work/android-ndk-r6/samples/hello-jni

[email protected]:~/work/android-ndk-r6/samples/hello-jni$ ndk-build
Gdbserver : [arm-linux-androideabi-4.4.3] libs/armeabi/gdbserver
Gdbsetup : libs/armeabi/gdb.setup
Compile thumb : hello-jni <= hello-jni.c
SharedLibrary : libhello-jni.so
Install : libhello-jni.so => libs/armeabi/libhello-jni.so
[email protected]:~/work/android-ndk-r6/samples/hello-jni$ $NDK_HOME/ndk-buildGdbserver : [arm-linux-androideabi-4.4.3] libs/armeabi/gdbserver
Gdbsetup : libs/armeabi/gdb.setup
Install : libhello-jni.so => libs/armeabi/libhello-jni.so

把官方自带的hello-jni的工程导入到Eclipse中运行

官方实例：android ubuntu ndk jni hello-jni

把上面的代码贴出来让大家看一下：

java文件

/* * Copyright (C) 2009 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package com.example.hellojni; import android.app.Activity; import android.widget.TextView; import android.os.Bundle; public class HelloJni extends Activity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); /* Create a TextView and set its content. * the text is retrieved by calling a native * function. */ TextView tv = new TextView(this); tv.setText( stringFromJNI() ); setContentView(tv); } /* A native method that is implemented by the * 'hello-jni' native library, which is packaged * with this application. */ public native String stringFromJNI(); /* This is another native method declaration that is *not* * implemented by 'hello-jni'. This is simply to show that * you can declare as many native methods in your Java code * as you want, their implementation is searched in the * currently loaded native libraries only the first time * you call them. * * Trying to call this function will result in a * java.lang.UnsatisfiedLinkError exception ! */ public native String unimplementedStringFromJNI(); /* this is used to load the 'hello-jni' library on application * startup. The library has already been unpacked into * /data/data/com.example.HelloJni/lib/libhello-jni.so at * installation time by the package manager. */ static { System.loadLibrary("hello-jni"); } }
c文件

/* * Copyright (C) 2009 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. * */ #include <string.h> #include <jni.h> /* This is a trivial JNI example where we use a native method * to return a new VM String. See the corresponding Java source * file located at: * * apps/samples/hello-jni/project/src/com/example/HelloJni/HelloJni.java */ jstring Java_com_example_hellojni_HelloJni_stringFromJNI( JNIEnv* env, jobject thiz ) { return (*env)->NewStringUTF(env, "Hello from JNI !"); } 














															

																					

								

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