ubuntu上最使用jni最简单易懂的例子

package com.example.firstjni;

public class JniClient {
	    static public native String AddStr(String strA, String strB);
	    static public native int AddInt(int a, int b);
}

2.生成 .h 的c++头文件

(1)用cmd命令定位到JniClient.class 所在目录，输入“javac JniClient.java“后回车，生成JniClinet.class文件（如果是用的Eclipse建的工程，在TestNdk\bin\classes\com\ndk\test目录下就已经有JniClinet.class文件了）。com.example.firstjni

(2)将JniClinet.class拷贝到FirstJni\bin\classes\com\example\firstjni目录，将cmd命令定位到FirstJni\bin\classes目录，输入”javah com.example.firstjni.JniClient“后回车，在FirstJni\bin\classes目录下就生成了C++头文件com_example_firstjni_JniClient.h

图片讲解如下：

com_example_firstjni_JniClient.h的文件内容如下：

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

#ifndef _Included_com_example_firstjni_JniClient
#define _Included_com_example_firstjni_JniClient
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     com_example_firstjni_JniClient
 * Method:    AddStr
 * Signature: (Ljava/lang/String;Ljava/lang/String;)Ljava/lang/String;
 */
JNIEXPORT jstring JNICALL Java_com_example_firstjni_JniClient_AddStr
  (JNIEnv *, jclass, jstring, jstring);

/*
 * Class:     com_example_firstjni_JniClient
 * Method:    AddInt
 * Signature: (II)I
 */
JNIEXPORT jint JNICALL Java_com_example_firstjni_JniClient_AddInt
  (JNIEnv *, jclass, jint, jint);

#ifdef __cplusplus
}
#endif
#endif

# 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.
#
LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)

LOCAL_MODULE    := FirstJni
LOCAL_SRC_FILES := com_example_firstjni_JniClient.c

include $(BUILD_SHARED_LIBRARY)

4. 将刚刚手动生成的com_example_firstjni_JniClient.h拷贝到FirstJni工程的jni目录下，

然后新建一个com_example_firstjni_JniClient.c文件完成头文件中函数的实现，其内容如下（本来想写两个方法的，现在只讲解第一个方法，返回一个字符串“HelloWorld from JNI ”,另一个方法是一个a+b的运算，方法写到这里，感兴趣的可以自己去研究）：

com_example_firstjni_JniClient.c

#include "com_example_firstjni_JniClient.h"
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

#ifdef __cplusplus
extern "C"
{
#endif
/*
 * Class:     com_ndk_test_JniClient
 * Method:    AddStr
 * Signature: (Ljava/lang/String;Ljava/lang/String;)Ljava/lang/String;
 */
JNIEXPORT jstring JNICALL Java_com_example_firstjni_JniClient_AddStr
  (JNIEnv *env, jclass arg, jstring instringA, jstring instringB)
{
    jstring str = (*env)->NewStringUTF(env, "I am chenyu, This is my first ubuntu jni!!!!");
    return str;
}

/*
* Class:     com_ndk_test_JniClient
* Method:    AddInt
* Signature: (II)I
*/
JNIEXPORT jint JNICALL Java_com_example_firstjni_JniClient_AddInt
  (JNIEnv *env, jclass arg, jint a, jint b)
{
    return a + b;
}

#ifdef __cplusplus
}
#endif

5.在MainActivity.java中完成对JniClient.java中函数的调用(首先静态加载动态链接so库)：

package com.example.firstjni;

import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.TextView;

public class MainActivity extends ActionBarActivity {

	 public String string1 = "I am chenyu ";
	 public String string2 = "this is my first ubuntu jni";
	 public int a = 3;
	 public int b = 5;
	 static {
		 System.loadLibrary("FirstJni");
	 }

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
        TextView  tv = new TextView(this);
        tv.setText(JniClient.AddStr(string1, string2)+"3 + 5 = " + JniClient.AddInt(a, b));
        setContentView(tv);
	}

	@Override
	public boolean onCreateOptionsMenu(Menu menu) {
		// Inflate the menu; this adds items to the action bar if it is present.
		getMenuInflater().inflate(R.menu.main, menu);
		return true;
	}

	@Override
	public boolean onOptionsItemSelected(MenuItem item) {
		// Handle action bar item clicks here. The action bar will
		// automatically handle clicks on the Home/Up button, so long
		// as you specify a parent activity in AndroidManifest.xml.
		int id = item.getItemId();
		if (id == R.id.action_settings) {
			return true;
		}
		return super.onOptionsItemSelected(item);
	}
}

五、demo已经上传，需要的猛搓下面的地址