Android------JNI 数据类型转换

ndk可以用代码1调用 ， 但例子中是用代码2。代码2可能是c++中的标准语法，代码1是ndk的。引用时要注意

代码1：env->GetStringUTFChars(str)

代码2：(*env)->NewStringUTF(env, str);

#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);  
//env->ReleaseStringUTFChars(str, szStr); 应该是这句
 }  
 //-----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;  
}  

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 + " ");  
  }  
  
 }