在JNI中如何将jobject类型转换为jdouble类型

发布网友发布时间：2022-04-24 07:32

共2个回答

热心网友时间：2022-06-17 15:44

#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 + " ");
  }

}

}

追问jdouble作为参数类型直接传可以用，但是我那要从一个传入的Java自定义对象中解析出jdouble类型的数据，就不行。

热心网友时间：2022-06-17 15:45

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

jfloat f) {

float fl = f