JNI 数据类型转换

 

#include <jni.h>

#include "com_test_Test.h"

#include <stdio.h>

#include <stdlib.h>

#include <strings.h>

 

//获取字符串

JNIEXPORT void JNICALL Java_com_test_Test_sayHello(JNIEnv * env, jobject obj,

  jstring s) {

 

 char * str = (char *) (*env)->GetStringUTFChars(env, s, 0);

 printf("\n c-string: hello - %s", str);

 

}

 

//获取，返回int

JNIEXPORT jint JNICALL Java_com_test_Test_add(JNIEnv * env, jobject obj,

  jint a, jint b) {

 int i = a;

 int j = b;

 printf("\n c-int: %d - %d", i, j);

 char str[256];

 sprintf(str, "%d", i + j);

 return (jint) i + j;

}

 

//获取，返回float

JNIEXPORT jfloat JNICALL Java_com_test_Test_getFloat(JNIEnv * env, jobject obj,

  jfloat f) {

 float fl = f;

 printf("\n c-float: %3f", fl);

 

 fl = 200.555;

 return (jfloat) fl;

}

 

//获取，返回 double

JNIEXPORT jdouble JNICALL Java_com_test_Test_getDouble(JNIEnv * env,

  jobject obj, jdouble dou) {

 double d = dou;

 printf("\n c-double: %3f", d);

 

 d = 800.88;

 return (jdouble) d;

}

 

//获取，返回boolean

JNIEXPORT jboolean JNICALL Java_com_test_Test_getBoolean(JNIEnv * env,

  jobject obj, jboolean bool) {

 

 unsigned char b = bool;

 printf("\n c-boolean: %lu  ", b);

 if (b) {

  printf("true");

 } else {

  printf("false");

 }

 

 b = 1;

 return (jboolean) b;

}

 

//获取，返回 string

JNIEXPORT jstring JNICALL Java_com_test_Test_getString(JNIEnv * env,

  jobject obj, jstring s) {

 char * st = (char *) (*env)->GetStringUTFChars(env, s, 0);

 printf("\n c-string:  %s", st);

 

 char * str = "hello wang wu!";

 jstring rtn;

 rtn = (*env)->NewStringUTF(env, str);

 return rtn;

}

 

//获取，返回 string []

JNIEXPORT jobjectArray JNICALL Java_com_test_Test_getStringArray(JNIEnv * env,

  jobject obj, jobjectArray arr) {

 int len = (*env)->GetArrayLength(env, arr);

 printf("\n c-stringArray :");

 int i = 0;

 for (i = 0; i < len; i++) {

  jobject obj = (*env)->GetObjectArrayElement(env, arr, i);

  jstring str = (jstring) obj;

  const char * szStr = (*env)->GetStringUTFChars(env, str, 0);

  printf(" %d-%s ", i, szStr);

  (*env)->ReleaseStringChars(env, str, szStr);

 }

 //-----返回----

 

 jstring str;

 jobjectArray args = 0;

 jsize size = 5;

 char* sa[] = { "Hello,", "world!", "zhang", "san", "yuang" };

 int j = 0;

 jclass objClass = (*env)->FindClass(env, "java/lang/String");

 args = (*env)->NewObjectArray(env, size, objClass, 0);

 for (j = 0; j < size; j++) {

  str = (*env)->NewStringUTF(env, sa[j]);

  (*env)->SetObjectArrayElement(env, args, j, str);

 }

 return args;

}

 

-----------------------------------------------------------------

 

下面是Test.java

 

package com.test;

 

public class Test {

 private native void sayHello(String str);

 

 private native int add(int a, int b);

 

 private native float getFloat(float f);

 

 private native double getDouble(double d);

 

 private native boolean getBoolean(boolean b);

 

 private native String getString(String str);

 

 private native String[] getStringArray(String[] sa);

 

 static {

  System.loadLibrary("Test");

 }

 

 public static void main(String[] args) {

  Test test = new Test();

  test.sayHello("zhang san");

  System.out.println("int     --> " + test.add(10, 20));

  System.out.println("float   --> " + test.getFloat((float) 20.123));

  System.out.println("double  --> " + test.getDouble(100.369));

  System.out.println("boolean --> " + test.getBoolean(true));

  System.out.println("string  --> " + test.getString("wang Wu"));

 

  String[] ss = { "hello", "-", "zhang", "san" };

  Object[] obj = test.getStringArray(ss);

  System.out.print("string[]-->  ");

  for (Object object : obj) {

   System.out.print(object + " ");

  }

 }

}

 

出处 : http://dolphin-ygj.iteye.com/blog/519492